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I

OISD-STD-128

FOR RESTRICTED CIRULATION ONLY

INSPECTION OF

UNFIRED PRESSURE VESSELS

OISD - STANDARD-128 First Edition, November 1988

Amended edition, August, 1999 Revised edition October, 2010

OIL INDUSTRY SAFETY DIRECTORATE Government of India

(Department of Petroleum & Natural Gas)

Website : www.oisd.gov.in

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II

OISD–STD-128

First Edition, November, 1988 Amended edition, August, 1999

Revised edition October, 2010 FOR RESTRICTED CIRULATION ONLY

INSPECTION OF

UNFIRED PRESSURE VESSELS

Prepared by

FUNCTIONAL COMMITTEE ON INSPECTION OF UNFIRED PRESSURE VESSELS

OIL INDUSTRY SAFETY DIRECTORATE 7TH Floor, NEW DELHI HOUSE,

27, BARAKHAMBA ROAD, NEW DELHI - 110 001.

Website : www.oisd.gov.in

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III

NOTE

OISD publications are prepared for use in the Oil and gas industry under Ministry of Petroleum and Natural Gas. These are the property of Ministry of Petroleum and Natural Gas and shall not be reproduced or copied and loaned or exhibited to others without written consent from OISD.

Though every effort has been made to assure the accuracy and reliability of the data contained in these documents, OISD hereby expressly disclaims any liability or responsibility for loss or damage resulting from their use. These documents are intended only to supplement and not to replace the prevailing statutory requirements.

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IV

FOREWORD

The Oil Industry in India is nearly 100 years old. Due to various collaboration agreements, a variety of international codes, standards and practices have been in vogue. Standardisation in design philosophies and operating and maintenance practices at a national level was hardly in existence. This, coupled with feed back from some serious accidents that occurred in the past in India and abroad, emphasized the need for the industry to review the existing state of art in designing, operating and maintaining oil and gas installations. With this in view, the Ministry of Petroleum & Natural Gas, in 1986, constituted a Safety Council assisted by Oil Industry Safety Directorate (OISD), staffed from within the industry, in formulating and implementing a series of self regulatory measures aimed at removing obsolescence, standardising and upgrading the existing standards to ensure safer operations. Accordingly, OISD constituted a number of Functional Committees comprising of experts nominated from the industry to draw up standards and guidelines on various subjects. The present document has been prepared by the Functional Committee on “Inspection of Unfired Pressure Vessels”. This document is based on the accumulated knowledge and experience of industry members and the various national and international codes and practices. It is recognised that failure of internals of a pressure vessel may only affect its performance and at most times may not materially affect the safety of the vessel. However, it is also recognised that failure of an internal component may lead to unit upsets which in turn could lead to a leak of hydrocarbons. Keeping this in view the Committee decided to include inspection of internals also as a part of this standard. This document is meant to be used as a supplement and not as a replacement for existing codes and practices. It is hoped that the provisions of this document, when adopted may go a long way to improve the safety and reduce accidents in the Oil and Gas Industry. Users are cautioned that no standard can be a substitute for the judgment of a responsible qualified inspection Engineer. Suggestions are invited from the users, after it is put into practice, to improve the document further.

This standard in no way super cedes the statutory regulations

of CCE, Factory Inspectorate or any other Govt. body which must be followed as applicable.

Suggestions for amendments to this document should be addressed to

The Co-ordinator, Functional Committee on

“Inspection of Unfired Pressure Vessels, Oil Industry Safety Directorate, 7th Floor, “New Delhi House”

27, Barakhamba Road, New Delhi – 110 001

Website : www.oisd.gov.in

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VI

FUNCTIONAL COMMITTEE MEMBERS (Second edition October 2010)

S.N. Name Organisation Position in Functional Committee

1. Mr. R. Wadhawan BPCL, Mumbai Team Leader 2. Mr. K.R. Soni IOCL Member 3. Mr. Krishna Hegde MRPL Member

4. Mr. D. Arthur Manohar CPCL Member

5. Mr. Balagangadharan, BPCL, Kochi Member 6. Mr. P.S. Murthy HPCL Member 7. Mr. L.R. Jain BPCL Member 8. Mr. J.P. Sinha IOCL, P/L Member 9. Mr. Debashis Mitra HPCL Member 10. Mr. S.C. Gupta OISD Member 11. Mr. Shamsher Singh OISD Member, Co-ordinator FUNCTIONAL COMMITTEE MEMBERS (August 1999) --------------------------------------------------------------------------------------------------------------------------- S.N. Name and Designation Position in Organisation Committee --------------------------------------------------------------------------------------------------------------------------- 1. Sh. R.K. Sabharwal CMNM-IOC (R & P) Leader 2. Sh.A.S. Soni DGM (P)-ONGC Member 3. Sh.R.H. Vohra DGM-(E) IOC (Mktg.) Member 4. Sh.D.P. Dhall CH INSP & AE MGR-BPC (REF) Member 5. Sh.P. Dasgupta Sr.Manager( Inspection) IOC Member

(R & P) 6. Sh.I.M. Advani MGR (PROJ) HPC (REF) Member 7. Sh.R.M.N. Marar Jt.Director OISD Member

Co-ordinator. --------------------------------------------------------------------------------------------------------------------------- In addition to the above, several other experts from the industry contributed in the preparation, review and finalisation of this document.

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VII

CONTENT

S. N. SECTION PAGE

1.0 Introduction 01

2.0 Scope 01

3.0 Definition 01

4.0 Role of Inspection 02

5.0 Stages of Pressure Vessel Inspection 02

6.0 Frequency of Inspection 03

7.0 Inspection Checks 05

8.0 Inspection During Maintenance 16

9.0 Re-rating of pressure vessels 16

10.0 Documentation 17

11.0 References 18

ANNEXURES: I A Typical Pre-commissioning Check List 19

II A Typical Checklist for In service Inspection 21

III Guidelines on Pressure Testing of Pressure Vessels 23

IV Corrosion Rate and Remaining Life Calculation 25

V Inspection Documentation Cards (Forms) 26

VI Inspection of Welding 31

VII Hydrogen Blisters-inspection, Evaluation and Repair of 34

VIII Inspection Tools 36

IX Likely Areas of Metal Deterioration 37

OISD-128 1 __________________________________________________________________________________________

INSPECTION OF UNFIRED PRESSURE VESSELS

1.0 INTRODUCTION

Safety in petroleum installations comes through continuous efforts at all stages. It can be ensured by observing that plant & equipment are designed, constructed, tested and maintained as per established engineering standards; and subsequent modifications and repairs are conforming to the same standard.

2.0 SCOPE

This standard covers minimum inspection requirements, types of inspections, inspection frequencies, inspection procedures and repair methodology for unfired pressure vessels, including underground pressure vessels installed in hydrocarbon industry. This standard excludes all mobile and portable pressure vessels such as truck & rail wagon mounted, gas cylinders which are covered in other OISD Standards.

3.0 DEFINITIONS 3.1 AUTHORISED PERSON

A qualified and experienced person authorized to perform pressure vessel inspections by the owner organization.

3.2 APPLICABLE STANDARD

Applicable standard refers to the original standard of construction, unless the original standard of construction has been superseded or withdrawn from publication, in this event, applicable standard means the current edition of the appropriate standard.

3.3 DEFECT

An imperfection, whose type or size, exceeds the applicable acceptance criteria

3.4 HOLD POINT

A point in the repair or alteration process beyond which work should not proceed until the required inspection has been performed and documented.

3.5 INJECTION POINT

Locations where relatively small quantities of materials are injected into process streams.

3.6 IN-SERVICE

Pressure vessel that have been placed in operation, as opposed to new pressure vessel prior to being placed in service.

3.7 MAXIMUM ALLOWABLE WORKING

PRESSURE (MWAP)

The maximum gauge pressure permitted at the top of a pressure vessel in its operating position for designated temp

3.8 NDE

Non Destructive Examination

3.9 ON STREAM

Pressure vessel has not been prepared for an internal inspection and it is containing any amount of process fluid.

. 3.10 OUT OF SERVICE

Pressure vessel containing no amount of process fluid and has been taken out of stream/ service for performing inspections/ repair.

3.11 PRESSURE VESSEL

A pressure vessel is a closed container designed to hold gases or liquids at a pressure different from the ambient pressure.

OISD-128 2 __________________________________________________________________________________________

3.12 SHALL Indicates mandatory requirement.

3.13 SHOULD

Indicates recommendation or that which is advised but not mandatory

3.14 Repair

The work necessary to restore a pressure vessel to a condition suitable for safe operation at the design conditions.

4.0 ROLE OF INSPECTION

The Authorized Person(s) performing the inspections shall be suitably qualified and experienced. The requisite criteria for deciding the qualification and experience shall be decided by the individual organization. Typical role of inspection personnel inter-alia is;

I) To prepare and implement inspection schedules to meet requisite standard, statutory and or quality requirements

II) To measure and record the

corrosion/ deterioration rates and to evaluate the current physical condition of the pressure vessel for soundness for continuation in service.

III) To co-relate the corrosion/

deterioration rate with design life for further run of the Pressure Vessel.

IV) To investigate the causes of

deterioration and recommend remedial measures, such as short term and long term repairs/ replacements.

V) To perform various stages of

inspections and maintain inspection records & Pressure Vessel history.

5.0 STAGES OF PRESSURE VESSEL INSPECTIONS

5.1 INSPECTION DURING PRE-

COMMISSIONING The pre-commissioning inspection of pressure vessels shall be performed to ensure that all examinations and tests during fabrication, erection and hydro-testing have been carried out in line with the design standard/ approved procedure. This inspection also includes the scrutiny of all the related records. A typical pre-commissioning checklist is placed at Annexure- I.

5.2 IN-SERVICE (EXTERNAL)

INSPECTION 5.2.1 Each above ground pressure vessels

shall be subjected to external visual inspection including aided visual inspection techniques such as thermography, X-ray profiling where ever applicable.

5.2.2 The inspection shall determine the

condition of insulation, painting, supports, cathodic protection, earthing etc and allowance for expansion, general alignment of the vessel on its supports, small bore piping etc.

5.2.3 Any deviation in the above or any sign

of leakage from nozzle flange/ mounting shall be investigated to identify the cause to take corrective measures. Vessels shall be examined for visual indications of bulging, out of roundness, sagging and distortion

5.2.4 Inspection for corrosion under

insulation (CUI) shall be considered for externally insulated pressure vessels operating between - 4 degrees C & 120 degrees C and vessels in intermittent service. This inspection may require removal of some insulation from suspected areas.

5.2.5 Internally lined pressure vessels

operating at high temperatures shall be checked for external hot spots to assess lining condition.

OISD-128 3 __________________________________________________________________________________________

5.2.6 Special attention shall be given to pressure vessels in humid area, areas near to cooling tower and in areas where corrosive chemical vapours are present to check for external corrosion and thickness reduction due to exposure to corrosive stream.

5.2.7 Whenever there is plant upset, those pressure vessels which experience excessive pressure / temperature shall be externally inspected immediately.

5.3 OUT OF SERVICE

(COMPREHENSIVE) INSPECTION 5.2.8 The out of service inspection of

pressure vessel shall be carried out to assess the integrity of the equipment, condition of internals and to determine the corrosion rate to estimate the remaining life. The inspection strategy/ program shall be designed based on the likely hood and consequences of damages because of the prevailing internal service/ environment conditions. The appropriate NDT techniques such as Liquid penetrant test (LPT), Magnetic particle test (MPT), Ultrasonic test (UT), Radiography etc. shall be deployed for condition assessment.

5.2.9 The thickness for all major components

(shells, heads, and cone sections) and a representative sample of vessel nozzles shall be measured, remaining life and next inspection interval shall be calculated for the limiting component. Adequate number of thickness measurement locations (TMLs) shall be defined to establish general and localized corrosion rates in different sections of the vessel.

5.2.10 Hydrostatic Pressure Testing

a) Hydrostatic pressure testing shall

be carried out for pressure vessels as per statutory requirements and also under the following conditions;

i) After any major alteration / re-

rating / replacement/ exposure to fire.

ii) After chemical cleaning

involving metal loss

iii) Out of service for more than 6 months

The duration of hydrostatic pressure testing shall be in line with the applicable code and not less than 30 minutes after stabilization.

b) Austenitic stainless steel pressure vessel shall be hydrostatic pressure tested using water with chloride content less than 50 PPM.

c) Stress due to hydrostatic pressure

testing shall not exceed 90% of the yield stress of the material of construction of the pressure vessel.

d) Hydrostatic pressure test shall not

be carried out at metal temperatures near the ductile-to-brittle transition temperature of the material.

e) Wherever the foundation,

internals like column trays and supports of the pressure vessel are not designed for hydrostatic load, suitable NDT or pneumatic test shall be considered with due approvals. The guidelines on pressure testing of pressure vessels are given in Annexure III.

6.0 FREQUENCY OF INSPECTION

The pressure vessel inspection frequency regime shall be arrived at so as to provide adequate information, necessary to declare that all the sections/ components of the pressure vessel, including the mountings, are safe to operate until the next scheduled inspection.

The following factors shall be considered while arriving at the inspection frequency regime for pressure vessels:

a) The nature of the fluid handled along with its pressure and temperature

OISD-128 4 __________________________________________________________________________________________

b) The risk associated with operational shutdowns and start-ups

c) Corrosion rates/ trends and

remaining corrosion allowance d) Increased corrosion rate due to

exposure of surfaces to changed environments

e) Findings and recommendations

of previous inspections f) The location of pressure vessels

such as in isolated, high-risk and highly corrosive areas.

g) The potential of air, water and

other environmental consequences.

h) Corrosion prevention and leak

detection systems. i) Applicable Statutory regulations

Identifying and evaluating, potential degradation mechanisms are important in assessment of probability or likelihood of pressure vessel failure. Combining the assessment of likely hood of failure and the consequences of failure in the form of a risk matrix may also be considered.

6.1 IN-SERVICE INSPECTION Each above ground vessel shall be externally visually inspected, once in two years. Insulated vessels operating between -4 deg C & 120 deg C shall also be externally inspected by removing insulation pockets at select locations.

6.2 OUT OF SERVICE INSPECTION The frequency of out of service inspection shall be determined based on history, corrosiveness of the fluid handled and operating conditions. The periods between these inspections shall not exceed one half of estimated remaining life of the vessel based on corrosion rate. However, the interval of out of service inspections shall not exceed five years.

In case, high corrosion rates are observed and half the remaining life is less than the above mentioned interval, then the out of service inspection interval shall be suitably reduced to ensure that maximum inspection interval shall not be more than half the remaining life. This is elaborated through examples as explained below; Example-1: 1. Total thickness allowance

available is 3 mm. 2. Corrosion rate is 0.5 mm per

year 3. Remaining life = 3/0.5= 6 years 4. Half remaining life = 3 years

5 Hence out of service (comprehensive) inspection interval shall not exceed 3 years

Example-2: 1. Total thickness allowance

available is 3 mm. 2. Corrosion rate is 0.25 mm per

year. 3. Remaining life = 3/0.25= 12

years. 4. Half remaining life = 6 years 5. Hence out of service

(comprehensive) inspection interval shall not exceed 5 years

The corrosion rate and remaining life shall be calculated as detailed in Annexure-IV

6.3 SPECIFIC INSPECTIONS

i) Pressure vessels installed in new process plants shall be inspected based on licensor recommendations or within first 2 years of operation to assess the internal conditions at select locations.

OISD-128 5 __________________________________________________________________________________________

ii) The internal inspection of

reactors and catalyst filled pressure vessels shall be carried out as and when the catalyst is dumped/ replaced. However, it is recommended that in-situ metallography be carried out at the time of replacement of catalyst, if necessary. The reactors and catalyst filled pressure vessels shall be inspected externally every two years and the internal inspection shall be carried out within 10 years.

iii) For pressure vessels where size

and configuration or lack of access makes vessel entry for internal inspection physically or operationally impossible, hydro-test and external inspection shall be carried out.

7.0 INSPECTION CHECKS

Prior to initiating the inspection of pressure vessels, the complete history of the vessel, design parameters, service, original thickness, corrosion allowance, corrosion rate and vulnerable locations of corrosion shall be ascertained. A sample list of tools required for pressure vessel inspection is attached at Annexure-VIII. A Typical Checklist for In service Inspection is attached at Annexure-II. The likely area of metal deterioration are described in Annexure-IX

Typical inspection procedures for major pressure vessels are as detailed below;

7.1 IN-SERVICE INSPECTION

The following shall be checked during the external inspection.

I) FOUNDATION AND SUPPORTS

a) Foundations

i) The foundations shall be

checked for spalling and cracking.

ii) Settlement shall be checked initially within the first month of operation till it gets stabilised and subsequently along with external inspection.

iii) Foundation bolts shall be

inspected for corrosion and damage.

iv) The nuts on anchor bolts shall

be inspected for tightness.

b) Skirts and Supports

i) Skirts shall be inspected for corrosion, distortion and cracking from outside as well as from inside.

ii) Condition of steel shall be

checked for external corrosion by removing the concrete at cracked locations.

iii) The weather proofing on the

extremities and fire proofing of structural supports shall be checked for water tightness.

iv) The condition of fire proofing

on support beams and skirts shall be inspected for bulging and cracks.

v) Skirt to shell weld joint shall

be checked for cracking.

c) Support of Horizontal Vessels

Horizontal vessels resting on concrete saddle supports where water can accumulate and cause external corrosion shall also be inspected. Horizontal vessels operating at high temperatures shall be checked to ensure free thermal expansion.

II) LADDERS,

STAIRWAYS,PLATFORMS AND STRUCTURES

a) These shall be inspected for

corrosion, cracks, paint failure etc.

OISD-128 6 __________________________________________________________________________________________

b) Bolts and nuts shall be checked for evidence of crevice corrosion.

c) Ladders shall be examined for

free movement to take up expansion of the vessels.

d) Drain holes on the platforms

shall be checked for proper draining.

III) INSULATION AND

PROTECTIVE COATINGS

a) Insulation shielding shall be checked for proper sealing at joints.

b) Condition of the metal

underneath shall be checked at inspection window.

c) Paint or protective coating shall

be examined for peeling or rusting.

d) The insulation retaining rings

shall be checked for moisture trapping.

IV) EARTHING CONNECTIONS

a) Earthing connections shall be

examined for loose bolting, proper welding, and electrical continuity.

b) The cable shall be examined for

broken strands. c) Earthing resistance shall be

checked at intervals as outlined in OISD-STD-137.

V) NOZZLES AND SMALL

CONNECTIONS

a) The nozzles shall be inspected for any visible corrosion, damage and leaks.

b) The tell-tale hole in the

reinforcement pad shall be checked for possible leaks.

c) Special attention shall be given

for suspected leaks/ corrosion at nipples used for instrumentation connections.

d) Check for full length engagement of thread connections.

VI) EXTERNAL INSPECTION OF

METAL SURFACE

a) The external surface shall be inspected for any sign of deterioration due to atmospheric corrosion, hydrogen blistering, cracks, mechanical damage, buckling & bulging etc.

b) The weld joints and heat affected

zones (HAZ) shall be checked visually for cracks. In case of doubt it should be checked by dye penetrant test.

c) Hot spots, which might have

developed on the outer surface due to the failure of internal linings of lined vessels, shall be checked. The areas, which have developed hot spots during service, shall also be checked for mechanical damage such as gouges and dents, leaks, cracks and oxidation of any external stiffeners.

d) Thickness measurement of the

shell and domes may be taken from outside. Exact location of thickness measurement may be decided after internal inspection only.

e) LPG Bullets and spheres having

fire proofing on the outside surface shall be examined for cracks, spalling, bulging and deterioration of fire proofing. Appearance of rust stains on the surface of fire proofing is an indication of presence of corrosion of metal underneath. If above indications are apparent the fire proofing in suspected areas shall be removed and the external surface shall be inspected for any corrosion.

OISD-128 7 __________________________________________________________________________________________

VII) MOUNDED STORAGE VESSELS

a) Vessel Settlement

i) Settlement of the vessel shall

be monitored once in six months and the readings shall be compared with the original readings for identifying the overall and differential settlements.

ii) The bottom nozzle supports

shall be adjusted so as release undue stresses on it and also provide support to it.

iii) The frequency of monitoring of

the readings can be reduced to once in a year if no differential / further settlement is observed in two consecutive inspections.

b) Mound External Surface

i) The erosion protection layer of

the mounds shall be inspected for damage at six months intervals and corrective action for restoration shall be taken.

ii) Special attention shall be given

to the run wild vegetation on the damaged spots. Drooping vegetation may indicate presence of gas in the mound.

iii) The bleeding of water along

the mound bottom might indicate the damage to the impervious layer (e.g. UPVC sheet) laid on top of the mound. Similarly, visual inspection shall be carried out in the bottom sand drains (if provided) for the bleeding of sand through drains. In such cases, remedial action including repairs / replacement of UPVC layer shall be under taken. Rain water accumulation inside the mound shall be avoided as this can lead to instability of the mound.

c) Cathodic Protection System CP system of the vessel shall be monitored as per the requirements of OISD-STD-150.

7.2 OUT OF SERVICE INSPECTION

CHECKS

The out of service inspections shall include both external and internal inspections.

7.2.1 GENERAL CONSIDERATIONS

i) Pressure vessel entry shall be made only with an applicable work permit as detailed in OISD-STD-105 on work permit systems.

ii) The area to be inspected internally shall be decided based on the history of the equipment. The history shall supplement the standard inspection procedure of the equipment.

iii) The tray man-ways shall be opened and the complete inspection shall be carried out.

iv) Carbon steel nozzles may be hammer tested.

v) Small bore nozzles (less than 50mm) are difficult to be thickness surveyed ultrasonically. The thickness may be determined by deploying digital radiographic techniques.

vi) The lined nozzles shall be checked thoroughly for leaks. Any leakage will indicate damage of the lining.

vii) If caustic is stored or used in a vessel it shall be checked for caustic embrittlement. The areas around the nozzles and in or adjacent to weld seams are susceptible to cracking.

7.2.2 VESSELS IN HIGH TEMPERATURE

SERVICE

OISD-128 8 __________________________________________________________________________________________

a) Pressure vessel which operates on thermal cycle like coke chamber and at high temperature like orifice chamber in FCCU, shall be thoroughly inspected from outside for any possible bulging/ cracking.

b) In case of coke chamber, if the

entry of feed is at the bottom, insulation of at least 2 to 3 courses all around shall be removed. The skirt to shell weld joints shall be thoroughly checked for cracks. The bottom flange welding with the shell shall also be inspected. The weld joints, heat affected zone (HAZ) and shell of 2 to 3 courses shall be checked for cracks and apparent bulging etc.

c) Presence of suspected cracks

should be confirmed by using suitable NDT techniques.

7.2.3 Preliminary visual inspection

i) Prior to scheduled shutdown of the unit the pressure vessel shall be examined from the outside to detect any unusual condition during operation, such as leaks in nozzle welds through tell-tale holes or gaskets, the condition of the bolts and flanges, the apparent condition of insulation and any other visible defects.

ii) During shutdown, before cleaning

the column/ vessel from inside, preliminary internal inspection shall be done. Observations regarding internal dislodging etc. shall be noted. Samples of deposits shall be collected for analysis. Preliminary inspection shall reveal the areas having deposits, scales etc. requiring thorough cleaning to detect metal wastage underneath the deposits during detailed inspection. After the preliminary inspection, internal cleaning shall be undertaken.

7.2.4 DETAILED INTERNAL INSPECTION

I) VERTICAL VESSELS (COLUMNS)

The inspection of a column can be divided into the top, feed and bottom zones.

a) Top Zone

i) Top dome, shell and internals in the top zone shall be visually inspected to locate corrosion, erosion, hydrogen blistering, cracking, mechanical damage etc.

ii) Special attention shall be given to

weld joints and surface conditions. If pits are noticed, depth of pits should be measured.

iii) Shell plates below the reflux

nozzle shall be inspected for any possible grooving. Reflux collector shall be checked for thinning.

iv) Spouts and counter spouts shall

be checked by hammer testing for finding any possible deterioration.

v) The trays and valves/ bubble

caps shall be checked for pitting and cracking.

vi) Thickness of dome and shell

shall be checked in all four compass directions (E, W, N and S). Thickness in dome section shall also be taken in the knuckle/ crown area. Thickness around all the nozzles shall be taken.

vii) Sample thickness of column

internals like downcomer, downcomer collectors and support plates should be taken. Besides this, if at certain locations of shell or dome, corrosion is observed thickness shall be measured at these locations to know the exact loss. Shell at the downcomer collector level shall be checked for any possible liquid level corrosion in the form of grooving.

OISD-128 9 __________________________________________________________________________________________

viii) Reference points should be marked on shell, dome and nozzles and same should be monitored for thickness during every inspection to determine rate of metal wastage.

ix) To check the condition of tray

support ring (TSR) at select locations, the tray sections shall be removed.

b) Feed Zone

i) The impingement plate shall be

checked for any corrosion, erosion and proper attachment with shell.

ii) Shell plates shall be inspected

near the impingement plate for erosion and attachment weld -cracks.

iii) The internals shall also be

inspected. Thickness of the shell plates in four directions and the impingement plate shall be taken.

iv) Sample thickness shall also be

taken on internals.

c) Bottom Zone

i) Bottom dome and shell shall be inspected to measure the thickness around bottom draw-off.

ii) If pitting is observed, pit depth should be measured.

iii) At steam injection points, the shell plate opposite to steam nozzles shall be thoroughly inspected for possible impingement.

iv) All internal piping etc. shall be inspected for any thinning, corrosion, deterioration, mechanical damage etc.

v) Thickness and hammer testing wherever possible should be carried out.

vi) All the nozzles including the manhole nozzles and retractable

spool piece shall be thickness surveyed.

vii) All nozzles in distributor shall be checked for blockage, erosion etc.

viii) In case of insulated column, insulation around nozzles should be removed to check for surface condition and facilitate thickness survey.

ix) Wherever, it is not possible to measure thickness from both inside and outside, ID measurements from inside shall be taken to determine thickness.

II) PRESSURE VESSELS IN

SPECIFIC SERVICE

a) Hydrogen Service

Pressure vessels in hydrogen service shall be thoroughly inspected for possible hydrogen damage like blistering, cracking, embrittlement etc. Hydrogen damage shall be inspected and evaluated as outlined in Annexure VII.

b) DEA/ MEA/ Caustic Service

Spot checking of T-weld joints shall be carried out for possible surface/ sub-surface cracks in the heat affected zone (HAZ). If defects or cracks are detected, 100% weld joints shall be checked.

c) Vessels in Sour Service

Vessel operating in sour service of carbon steel metallurgy shall be inspected with suitable NDT like Wet Fluorescent Magnetic Particle Inspection (WFMPI), Eddy Current etc. to identify the surface / sub surface cracks. Ultrasonic shear wave is deployed for sizing of defects after detection. Longitudinal Ultrasonic examination is deployed to find out metal loss and sizing / location of blistering. Avoid high hardness zones at weld / HAZ area. Limit

OISD-128 10 __________________________________________________________________________________________

the weld / HAZ hardness to 22 HRC and below.

d) Vessels in Liquid Nitrogen

Service

i) The liquid nitrogen storage vessel is typically jacketed, made of inner & outer vessels. The metallurgy of inner vessel is austenitic stainless steel and the outer vessel is carbon steel. The annulus between inner & outer vessel is filled with Perlite insulation and vacuum is established. The outer shell and nozzles shall be checked for metal loss and the welds shall be checked for any visible external corrosion.

ii) The annulus space vacuum shall be monitored to identify inner vessel leaks

iii) Pneumatic test or test with liquid

nitrogen (operating medium) for inner vessel is done at 1.1 times the design pressure.

Before carrying out the test, the safety valve should be set to the designated pneumatic test pressure to avoid over pressurization of inner vessel and the condition of burst / rupture discs in the vessel shall be checked for healthiness.

While using operating medium as the test fluid (cryogenic liquid), the inner vessel shall be pressurized by allowing the cryogenic liquid to vapourize and to develop the test pressure. The pressure shall be held for at least one hour.

After satisfactory completion of pressure test, the cryogenic liquid is gradually released from the inner shell to reach the operating pressure and the safety valve is reset to the design set pressure.

e) Internally Lined Vessels

i) Austenitic stainless steel columns

and columns lined with austenitic

stainless steel which are prone for Polythionic Acid attack shall be passivated as per the procedure given NACE RP 0170 before opening. Passivation shall be done as per the process licensor’s recommendations.

ii) All the integral cladding shall be

checked for bulging, erosion, disbonding etc.

iii) In case of strip-lined vessels

individual strips and associated welding shall be visually checked for bulging and cracks. Special attentions shall be given to the weld joints and heat affected zones (HAZ), where cracking can take place. If cracks are suspected, dye penetrant test should be carried out. The integrity of strip lining should be checked with air and soap solution. Thickness of the strips shall be measured at select locations to ascertain the thinning out of strips. The areas where the strip lining leaks have been noticed, a detailed inspection shall be carried out to check the base metal condition. Thickness survey of the strip lined column shall be done from outside to check the parent material thickness.

iv) The integrity of nozzle liner shall

be pneumatically tested at pressure not exceeding 0.5 Kg/cm2.

v) The junction of lined and unlined

sections shall be checked for galvanic corrosion.

f) Internally Painted/ Coated

Vessels i) Painting shall be visually

inspected and dry film thickness (DFT) shall be measured and compared with original DFT.

ii) FRE/ FRP linings shall be visually

checked for mechanical damage, cracks and holidays. Thickness of the pressure vessel shall be measured from outside

OISD-128 11 __________________________________________________________________________________________

The temperature limitations of the painting/ coating systems used inside the vessel should be known. While shutting down a unit, water flushing shall be resorted to instead of steam flushing or as recommended by the paint manufacturer. The painted surface shall be cleaned by water washing and then mopped. Cleaning with wire brush shall not be resorted to. Man entry shall be by wearing soft-shoes.

7.2.4 SPECIFIC INSPECTION CHECKS

FOR PROCESS UNITS

I) Fluidized Catalytic Cracking Unit (FCCU)

a) Reactor/ Regenerators/

Strippers of FCCU

i) In catalytic Reactors and Regenerators, the supporting bars for internal equipment such as cyclones shall be closely examined for erosion, crack etc. The cyclone assemblies, air distributor, disengaging device, internal abrasion resistant lining etc. are susceptible to catalyst erosion and shall be closely examined.

ii) Welding of the air grid supporting rings shall be checked for erosion and cracking. Out of roundness or bulging may be evaluated by measuring the diameter of the vessel at the cross section of maximum deformation and comparing it with the original diameter. If the bulging is at intervals, the measurement can be done by dropping a plumb line and taking the measurements at selected intervals. This shall also reveal the contour of the shell.

b) REACTORS

The reactor vessel operates in creep range; hence it is subjected to metallurgical degradation due to high temperature exposure. It is mandatory to assess the creep damage levels by micro structure examinations. The internals are

subjected to erosions due to catalyst movement. Therefore, each internal parts and the abrasive resistant lining shall be checked for erosion damage. The additional specific checks for reactor are as follows;

i) Thermo-wells shall be inspected for oxidation, cracking or distortion.

ii) Cyclone assembly shall be

inspected at locations like inlet horns, volute, dust bowl, gas risers etc for erosion.

iii) Dip leg along with flapper/ trickle

valve shall be inspected for erosion/ perforations/ plugging.

iv) Other internals like deflector

plate lining, grid cone lining and riser pipe shall be checked for erosion.

v) Stripper shell and steam nozzle

shall be inspected for erosion.

vi) Condition of the lining in the feed riser pipe shall be checked.

vii) Inspection of steam and catalyst

feed injections piping and nozzles shall be carried out.

viii) In the plenum chamber, shell

shall be inspected for erosion and thickness measurements shall be taken.

ix) In the anti-coking chamber,

peripheral holes shall be checked for plugging.

x) Cyclone supports should be

checked for erosion/cracking.

xi) Dissimilar weld joints exist in the riser pipe these should be checked for cracks.

xii) The Reactor and Regenerator

stand pipes shall be examined for failure of internal lining and metal deterioration.

xiii) The expansion bellows in the

stand pipes shall be checked for

OISD-128 12 __________________________________________________________________________________________

internal erosion of sleeve, refractory lining, perforation of convolutions etc.

xiv) The slide valve internals shall be

examined for erosion and proper operation.

c) REGENERATOR

The regenerator vessels are normally provided with internally erosion resistant insulating cast-able refractory. Based on the in service thermography survey, the identified areas of possible refractory damage shall be internally inspected. The additional specific checks for regenerator are as follows;

i) The refractory lining shall be

checked for erosion, spalling, cracking etc.

ii) Particular attention should be

given just near big manway and in the areas of possible turbulence.

iii) Aeration connections, thermo-

wells and trickle valves shall be inspected for possible erosion and damage.

iv) Cyclone assembly shall be

inspected at locations like inlet horns, volute, dust bowl, gas risers etc for erosion.

v) Dip leg along with flapper/ trickle

valve shall be inspected for erosion/ perforations/ plugging.

vi) Lining of the plenum chamber

and stack above the plenum chamber shall be inspected. If the plenum chamber is of SS material, the bimetal weld joint between chamber and shell shall be examined from inside.

vii) Steam rings shall be inspected

for oxidation/ erosion.

viii) Air distributor/ grid plates shall be checked for bulges/ erosion and thickness.

ix) Nozzles in the air distributor

assembly shall be checked for internal erosion. Grid plate shall be inspected for cracks or perforations. Overflow well and seal boxes shall be checked for erosion and perforations.

x) Lining of the cone below the air

grid shall be inspected for possible refractory damage.

xi) Auxiliary burner tips, air door and

the pilot shall be inspected visually.

d) ORIFICE CHAMBER/ DOUBLE

DISC SLIDE VALVE (DDSV)

i) The orifice chamber shell shall be inspected for erosion and bulging at baffle locations.

ii) The areas just after the Double

Disc Slide Valve (DDSV) shall be inspected critically.

iii) The holes/ sleeves on the grid/

baffle plate shall also be examined for increased diameter due to erosion.

iv) The DDSV internals shall be

examined for erosion and proper operation.

II) HYDROCRACKER/

HYDROTREATER

Reactor / pressure vessels including PSA (pressure swing absorber) vessels are subjected to following degradation mechanisms;

a) Metallurgical Degradation

i) High Temp. Hydrogen attack

ii) Temper Embrittlement

iii) Sigma phase formation / Sensitization of class 300 SS

iv) High temperature Stress Rupture

b) Corrosion Degradation

OISD-128 13 __________________________________________________________________________________________

i) Ammonium Bi-sulfide corrosion

ii) Polytheonic acid corrosion

iii) Wet H2S cracking

• Sulphide stress corrosion cracking

• Hydrogen induced cracking • Stress oriented hydrogen

induced cracking

iv) High temperature H2-H2S

v) Naphthenic acid Corrosion

Common problems with Reactor vessels are Gasket ring groove cracking, Cracks near bottom cone attachment, Tray attachment weld cracks, Nozzle weld cracking, Mid wall weld cracking etc.

Typical checks for reactor components are as given below;

S.N.

Component Inspection Techniques

1

Tray & Catalyst support cone attachment welds

Visual, Liquid penetrant Testing

2

Wire Mesh

Visual

3

Thermo well

Visual, Liquid penetrant Testing

4

Gasket Ring Groove

Liquid penetrant Testing

5

Nozzle & Manway Welds

WFMPI, AUT

6

Skirt Attachment welds

LPT,WFMPI, AUT

7

Girth / Longitudinal welds

WFMPI & AUT

In case of any defects are found then Carry out fitness of Service analysis and avoid repairs if possible. The equipment with Carbon steel / C-1/2 Mo steel is most likely affected equipment of hydrogen attack. Reactor screens are mostly affected by Sulfidation corrosion. The equipment which are operating beyond design limit are to be checked thoroughly for Sulfidation corrosion. Fractionator flash zone is prone to Sulfidation attack.

Specialized Ultrasonic inspection techniques like back scatter; velocity ratio, high sensitivity shear wave etc may be deployed for detection of high temp hydrogen attack (HTHA). Normally SS cladding reduces the effective hydrogen diffusion since it is much slower when compared to ferritic steel hence it is generally exempted from HTHA attack.

Injection points including small bore piping and instrument tapings are to be carefully examined using B-scan or radiographic inspection techniques.

III) MOUNDED STORAGE VESSEL

a) All the weld joints of the vessel shall be

examined through NDT techniques like Wet Fluorescent Magnetic Particle method, Dye Penetration Test hardness survey, and ultrasonic flaw detection to ensure the integrity of the joints.

b) The wall thickness of the vessel shall

be measured ultrasonically. c) In case of any indication of defect or

metal loss, the mound cover of the vessel shall be removed to expose the outer surface for necessary examination from outside, if required.

Any repairs or modifications undertaken shall be after due approval.

d) Vessel shall be subjected to hydro test

once every 10 years or at every welding to the vessel (repairs or new connections) whichever is earlier, by a competent person and records maintained.

OISD-128 14 __________________________________________________________________________________________

e) The settlement of the vessel shall be checked at least at 3 points along the length of the vessel.

Special attention shall be given to those areas where external coating deterioration is more likely to occur viz. near supports, fittings, reinforcement rings, field welds, bottom nozzles etc., while carrying out NDT. During visual inspection on the internals of the vessels, special attention shall be given to the stiffeners for identifying the following:

i) Local instability in the stiffeners

ii) In-plane buckling

iii) Shear buckling of the web

iv) Flange induced buckling

IV) RUBBER LINED PRESSURE VESSEL

The rubber lining shall be inspected for mechanical damage, holes, cracking, blistering, bonding etc. Holes in the lining are evidenced by bulging. A holiday detector should be used to thoroughly check the lining for leaks and holiday. Care must be taken so that the test voltage does not approach a value that might puncture the lining. The test voltages shall be selected based on the thickness of the rubber lining. Inspection of rubber lined vessels shall be carried out in line with IS-4682-Part-I.

V) RIVETED VESSELS

Riveted vessels shall be examined for tightness of rivets, soundness of caulking and seal welds and other conditions. For the insulated riveted vessel, insulation should be removed from all joints for checking as per statutory requirements.

7.3 MINIMUM/ RETIRING THICKNESS

The limiting or retiring thickness of any pressure vessel shall be determined as per the applicable design code to which it has been manufactured.

7.4 CORROSION COUPONS/PROBES

Corrosion coupons are installed in the pressure vessels to evaluate accurately the corrosion rate or to evaluate a new material in the existing environment. While doing the internal inspection the corrosion coupons if installed should be taken out. Nature of corrosion attack on the corrosion coupons shall be studied. The coupons are then thoroughly cleaned and weight loss in a specified length of time shall be calculated. This gives the corrosion rate and cleaned coupons are again installed for future evaluation. Corrosion probes may be installed at vulnerable locations on the pressure vessels for on-stream monitoring of corrosion rates. Coupons and probes can be either fixed or retractable type.

7.5 SAFETY RELIEF DEVICES

The safety valves and safety relief valves on the pressure vessels should be periodically inspected and tested as per OISD-Std-132.

8.0 SPECIFIC INSPECTIONS,

REPAIRS AND CHECKS AFTER REPAIRS

8.1 WELD BUILD UP

In pressure vessels where metal loss observed is limited to a small localized area and the remaining thickness is less than the minimum required thickness, repair by local weld filling may be required to build up the thickness. The area to be repaired should be marked and should be cleaned thoroughly. The area is filled with weld deposits, in a staggered manner to avoid warping, with suitable electrodes matching with the base part. After weld build up, the area should inspected for cracks and defects. Thickness shall be measured ultrasonically to check whether requisite thickness has been obtained. Preheating and post weld heat treatment whenever required should be carried out as applicable.

8.2 NOZZLE REPLACEMENT

OISD-128 15 __________________________________________________________________________________________

Thinned and deteriorated nozzles shall be replaced. New nozzles fabricated out of piping having thickness equivalent to original nozzles are installed. Welding including preheating and post weld heat treatment shall be carried out as per approved procedure. The weld joints shall be checked visually and also by dye penetrant test. Defects, if any, shall be repaired. The leaks from the nozzle welds shall be checked by pressurising with air at a pressure 1.03 kg/cm2 through the tell-tale hole provided in the reinforcing pad. The integrity of repaired weld shall be checked either by pressurizing the entire vessel or by pressurizing local area. In some cases where the area is accessible from inside, a box may be provided externally around the nozzle. The box is pressurised with water to the test pressure of the column/vessel calculated by applicable code. The weld joints and HAZ are checked for possible leaks. If any defect is found in the weld joints, these are gouged, re-welded and retested.

Pre heat and controlled deposition welding is to be considered in lieu of post weld heat treatment where PWHT is unadvisable or mechanically unnecessary. Prior to use any alternative method a metallurgical review needs to be conducted to find out whether proposed alternative is suitable for application. The review should consider reason for original PWHT, susceptibility to cracking, stresses in the location of welding, high temperature Hydrogen attack, susceptibility to creep damage etc. The controlled deposition welding shall be considered for material limited to P-1, P-3 & P-4 steels only. A detailed weld procedure specification shall be developed and qualified for each application. The welding technique shall be controlled deposition temper bead or half bead technique. Local PWHT may be substituted for all materials provided application is reviewed and a detailed procedure is developed. The required post weld heat temperature shall be maintained for a distance of not less than two

times the thickness of base metal thickness measured from weld. The PWHT shall be monitored by suitable number of thermo-couples.

8.3 PARTIAL REPLACEMENT OF SHELL

PLATES AND DOMES

Some portion of shell plates and domes of pressure vessels may get thinned due to corrosion or erosion. The thickness of the affected area may reach the retiring thickness. In such cases, partial replacement of shell plate or dome is carried out as weld repair of the big area is not practically possible. The affected portion is cut and removed. The new plates matching with the metallurgy and thickness of the original plate is made available.

The edge preparation shall be done as per the code requirement by grinding. The prepared edges shall be checked for cracks, flaws and defects by magnifying glass and by using dye penetrant kit. The welding procedure is developed for welding the old and new piece as per the relevant code. The welding may be performed either from inside or outside. The root run shall be thoroughly inspected for cracks and flaws. After completing the welding from one side, the other side is chipped and grounded. Before welding again, the groove is checked for cracks and defects. Welding is then completed from the other side. Complete welding shall be visually checked and radiographed as per the applicable code. Detailed inspection of welding shall be done as outlined in Annexure VI.

Preheat and post weld heat treatment shall be carried out as per the requirement of relevant code. In order to check whether post weld treatment has been carried out properly, hardness readings on the weldment and HAZ shall be taken after PWHT. The hardness readings should be minimum as the indentation marks required during hardness measurement act as stress riser and this leads to stress concentration. If post weld heat treatment is required it is recommended to carry out radiography before post weld heat

OISD-128 16 __________________________________________________________________________________________

treatment also. The defects in the welding are repaired by gouging and re-welding. In lieu of radiography, ultrasonic inspection of weld joints may be carried out.

8.4 REPAIR OF CLADDING AND

STRIPLINING

The bulged, cracked or heavily pitted cladding inside the pressure vessels shall be repaired. The deteriorated cladding is removed by cutting. The edges of the remaining cladding are sealed by welding, using proper electrodes as per cladding and shell metallurgy. If the area of the damaged cladding is small, the area is weld overlayed using suitable electrodes. The area is then ground smooth. The repaired portion shall be checked visually and by using D.P. for defects and cracks etc. The welding should be done in a staggered manner to avoid distortion of the shell. When the damaged area is big, after sealing the remaining cladding, strip lining of the area can be done. (Details of strip lining and welding procedure is given in Annexure - II). Bulged strip lining is replaced by puncturing the lining to remove entrapped air. The bulged portion of the lining is flattened by light hammering and then welded. If the strip lining has cracked or heavily pitted the damaged lining should be removed and fresh lining put. The weld joints are checked for flaws and cracks by DP and visual examination. While removing or puncturing the cladding/strip lining, necessary precautions should be taken as hydrocarbon may be entrapped in between the lining and shell.

The equipment operating in high temperature hydrogen service the following precaution shall be considered. a) Out gassing of base metals

b) Hardening of base metals due to welding, grinding or arc gauging.

c) Pre-heat and inter pass

temperature control Repairs shall be monitored closely. DP testing shall be carried out after repairs. Vessels made of P-3, P-4 & P-

5 shall be examined for cracking by ultrasonics. In case of low alloy steel vessels these examination needs to be carried out after a delay of 24 hours in order to take care of delayed cracking.

8.5 REPAIR OF PAINTED AND

RUBBERLINED AREAS

If the painting in a small area of a vessel has peeled off or has been damaged patch painting repair can be done. The damaged areas shall be painted with original painting system with proper curing time etc. If the area of damage is large, the area is shot blasted to Swedish, standard Sa 2-1-/2 to clean the surface and original painting system is applied with proper curing time. DFT is measured with paint thickness gauge. If internal rubber lining of vessels has bulged or cracked in a small area, the deteriorated lining shall be removed and fresh rubber lining is put in that small area. New lining shall be checked for holes and flaws. Local curing should be done to achieve hardness of 65 + 50A (shore hardness A). When a large area of the rubber lining has cracked and bulged, the damaged lining is taken out. Bare metal is cleaned by shot blasting. New rubber lining is provided. Curing shall be done to achieve 65 + 50A (shore hardness A). The lining shall be visually checked for cracks, holiday and bulging. The holidays shall be checked by using holiday detector. For inspecting the rubber lining IS-4682-Part I shall be referred.

8.6 HYDROSTATIC TEST

After satisfactory repair & inspection, the column/ vessel shall be hydrostatically tested as per clause 5.3.3

The guidelines on pressure testing of pressure vessels are placed at Annexure-III.

8.7 PNEUMATIC TESTING

Pneumatic testing may be used when hydrostatic testing is impracticable because of temperature, foundation,

OISD-128 17 __________________________________________________________________________________________

refractory lining or process reasons. However, the potential personnel and property risk of pneumatic testing shall be evaluated before such test is carried.

9.0 RE-RATING OF PRESSURE

VESSELS

Re-rating pressure vessels by changing the temperature rating or the MAWP shall be done only after all the following requirements are met i) All re-rating shall be established in

accordance with the requirements of the code to which the pressure vessel was built or by computing using the appropriate methods in the latest edition of the applicable code.

ii) Current inspection records verify that

the pressure vessel is satisfactory for the proposed service conditions and that the appropriate corrosion allowance is provided.

iii) Re-rated pressure vessel shall be

leak tested in accordance with the code to which the pressure vessel was built or the latest edition of the applicable code for the new service conditions, unless documented records indicate a previous leak test was performed at a greater than or equal to the test pressure for the new conditions. An increase in the rating temperature that does not affect allowable tensile stress does not require a leak test.

iv) Pressure vessel shall be checked to

affirm that required pressure relieving devices are present; are set at appropriate pressure; and have the appropriate capacity at set pressure.

v) All pressure vessel components in

the system, such as valves, flanges, bolts, gaskets etc. are adequate for the new combination of pressure and temperature.

vi) Appropriate engineering records are

updated.

vii) A decrease in the minimum operating temperature is justified by impact test results, if required by the applicable code.

10.0 DOCUMENTATION

Observations of each inspection shall be properly recorded. After determining the corrosion rate and remaining corrosion allowance, repair and replacement of a pressure vessel can be planned. The following cards as attached at Annexure-V shall be used for proper documentation of the Inspection findings:

i) Data card (Ref. Form No. 1)

ii) Index card (Ref. Form No. 2)

iii) History card (Ref. Form No.3)

iv) Data record card (Ref. Form No. 4)

v) Development sketch (Ref. Fig.5 & 6)

OISD-128 _______________________________________________________________________________________

18

11.0 REFERENCES

The following codes standards and publication have either been referred or used in the preparation of this standard, and the same shall be read in conjunction with this standard.

i) API Guide for Inspection of Refinery Equipment - Chapter VI - Unfired Pressure Vessels.

ii) API Guide for Inspection of Refinery Equipment - Chapter V - Preparation of Equipment for

Safe Entry and Work. iii) ASME - Pressure Vessel Code. Section VIII Divn. I & II. iv) Indian Standard for Unfired Pressure Vessels - IS-2825.

v) BS-5500-Specification for Unfired Fusion Welded Pressure Vessels. vi) API-510-(2007) Pressure Vessels, Inspection Code-Maintenance, Inspection, Rating,

Repair & Alteration.

vii) API-RP-572, Inspection of Pressure Vessels (Towers, Drums, Reactors, Heat Exchangers and Condensers)

viii) IS-9964 Part-I, Preparation of Tank for Safe Entry and Work. ix) IS-4682 part I, Code of practices for lining of vessels and equipment for chemical

processes-Rubber Lining. x) Pressure Vessel Inspection Safety Code-Part 12 Institute of Petroleum.

xi) Engineering Equipment Manufacturers and Users association - EEMUA 190

OISD-128 _______________________________________________________________________________________

19

Annexure-I page 1 of 2

A TYPICAL PRE-COMMISSIONING CHECKLIST

The check list format shall contain the following minimum information.

a) Equipment No.

b) Serial No.

c) Date of Inspection

d) Equipment Type

e) Plant

f) Service

g) Design Code

h) Manufacturer

i) Main Dimensions

j) Material of Construction

k) Max. Allow. working pressure/Vacuum

l) Max. Allow. Working Temperature

m) PWHT Radiography (Spot/Full)

n) Hydrostatic Test Pressure

CHECKLIST

1.0 Check documentation like Material Test Certificate (MTC), Procedure Qualification

Record (PQR), welding procedure Specification (WPS), Welders Qualification Records

QAP etc.

2.0 Check records of stage inspections such as joint fit ups, pre/ post weld heat treatment,

Radiography & other NDT tests, hydro test etc. 3.0 Check and inspect all nozzle connections including drains and vents 4.0 Check and inspect all threaded connections for proper tightening 5.0 Check for adequate engagement of threads, back welding and gusseting 6.0 Check for any alteration/ deviation from the drawing during fabrication 7.0 Ensure proper installation of internals. 8.0 Check for internal cleanliness before final boxing up. 9.0 Measure and record base line data of wall thicknesses. 10.0 Check and ensure installation of specified gaskets, especially at the untested joints. 11.0 Check installation and set pressure of pressure relieving devices.

OISD-128 _______________________________________________________________________________________

20

Annexure-I page 2 of 2 12.0 Check correct installation (direction) of check/ globe/control valves. 13.0 Check proper bolting of flange joints. 14.0 Check for proper alignment 15.0 Check for tension free jointing of piping connected to pressure vessel 16.0 Check painting for Dry Film Thickness (DFT). 17.0 Check insulation and fire proofing for proper installation/ sealing etc 18.0 Check records of coating on under grounded/ mounded vessels for bonding/ thickness/

holiday testing. 19.0 Check performance of cathodic protection system 20.0 Check earthing connections 21.0 Ensure free movement of vessel (thermal expansion) with respect to adjoining

structure, platforms etc. 22.0 Ensure ladders and landing platforms are meeting the standard norms and practices.

OISD-128 _______________________________________________________________________________________

21

Annexure -II

A TYPICAL CHECKLIST FOR IN SERVICE INSPECTION

i) Carry out Ultrasonic thickness gauging of the vessel operating at lower temperature. Larger the vessel, more readings are required to be assured of its condition. Record of previous internal inspections can be utilized to locate the areas subject to corrosion.

ii) Inspect the equipment for any local hot spots by thermography / visual inspection

particularly for internally refractory lined vessels, local corrosion, and gasket leaks.

iii) Check for condition of protective coating, insulation and fire proofing of structural members for adequacy of protection.

iv) Check the condition of bottom dished end to skirt weld for any rain water corrosion.

v) Check for bulging, out of roundness, sagging and distortion. If abnormality observed, the

overall dimensions of the vessel shall be checked to determine the extent of the distortion

vi) Check the condition of platform, hand rails and ladders for safety.

vii) Check the protective devices like safety valves, rupture discs for any passing / rupture. Thermo-graphy may be used to detect the passing of safety valves. Ensure that the block valves upstream and downstream of safety valves (if provided) are kept opened and car-sealed.

viii) Check and monitor the process parameters like pressure, temperature, throughput,

change in feed stock, pH control, sulphur, chloride content which will have a slow but long term impact on health of columns and vessels.

ix) Check the effectiveness and performance of corrosion inhibitors, caustic, ammonia and

other chemicals injected for corrosion protection.

x) Ensure the functioning of pressure gauges, temperature indicators and level gauges.

xi) Check the condition of anchor bolts and earthing connections.

All observations shall be recorded and filed in history file. In service inspection report shall be taken into account for shutdown work list and planning.

OISD-128 _______________________________________________________________________________________

22

Annexure-III page 1 of 3

Guidelines on Pressure Testing of Pressure Vessels

1) Introduction

It is a statutory obligation and a requirement to carry-out a pressure test on certain equipment at prescribed intervals. This section provides guidance on the pressure testing which may be carried-out once the service life has begun.

2) Purpose

Pressure testing of pressure vessel is carried-out for a variety of purposes in addition to that highlighted above.

a) Exposing inherent, major faults in a design or materials nature or serious errors

following a modification / repair. b) Ensuring that no significant defect has been missed on inspection, either inadvertently

or because of inadequate access for visual or NDE. c) Also, acts as a form of providing mechanical stress relief by levelling out of local areas

of high stress following a repair. 3) Circumstances calling for pressure test

a) Statutory requirements and as required by codes and standards b) To verify basic design, strength and integrity of the equipment following a repair or

modification on it. c) Following a change in design conditions (pressure / temperature combination) d) Inadequate access preventing a meaningful inspection and a pressure test is

acceptable in lieu e) To check the tightness of joints

4) Pressure test preparation

i) When a pressure test is to be conducted in which the test pressure will exceed the set pressure of the pressure relieving device(s), the pressure relieving device(s) should be removed. An alternative to removing the pressure relieving device(s) is to use test clamps to hold down the valve disks.

ii) All gages shall be calibrated against a standard dead weight tester or a calibrated master

gage. Gages shall be recalibrated at any time that there is reason to believe that they are in error.

iii) Dial indicating pressure gages used in testing shall be graduated over a range of about

double the intended maximum test pressure, but in no case shall the range be less than 1½ nor more than 4 times that pressure. Digital reading pressure gages having a wider range of pressure may be used provided the readings give the same of greater degree of accuracy as obtained with dial pressure gages.

iv) An indicating gage shall be connected directly to the vessel. If the indicating gage is not

readily visible to the operator controlling the pressure applied, an additional indicating gage shall be provided where it will be visible to the operator throughout the duration of the test. For large vessels, it is recommended that a recording gage be used in addition to indicating gages

OISD-128 _______________________________________________________________________________________

23

Annexure-III page 2 of 3 5) Test pressure

Actual pressure used during a test depends on the objective of the test.

a) Strength Testing: In this case a stress level greater than that experienced in service is induced (but lesser than that which would cause damage). Strength testing necessarily demonstrates that the equipment can safely withstand the maximum service pressure (at maximum operating temperature). The test pressure can be at the same level as the original test pressure (new equipment), but normally it is slightly less to allow for loss in thickness due to corrosion.

b) Leak Testing: It is carried-out where the objective is not to test the strength of the

equipment, but to detect the leakage (sometimes leakage rates). The pressure applied is generally less than design pressure. Normally, it is carried-out to detect leak tightness of gasket joints, tube to tube sheet joints etc.

6) Practical & Safety Aspects 6.1 Hydrostatic Testing

a) Some of the considerations which should be borne in mind during a pressure test are equipment foundations & supporting structure, ability of line supports and vessels nozzles to carry the test weight, ensuring that connected ancillary equipment (instrument, valves etc) are capable of withstanding the test pressure, including static head in the specified test pressure etc.

b) Other aspects to be considered are actual condition of the equipment. Usually,

equipment is not in the ‘new & cold’ condition of original construction. The test pressure should be gradually applied – initially to a value of 50% of the specified test pressure; thereafter the pressure shall be increased in stages of approximately 10% of the specified test pressure until this is reached.

c) The required test pressure shall be maintained for not less than 30 minutes except in the case of vessels less than 500mm diameter and 10mm thick. In such cases, it is permissible for the test period to be subject of agreement. As a general practice, minimum test duration of 30 minutes is considered adequate.

d) At no stage shall the vessel be approached for close inspection until the pressure has

been positively reduced to a level lower than that previously attained. “Previously attained” pressure indicates maximum operating pressure attained by the vessel during its service life. The pressure(s) at which the vessel will be approached for close inspection shall be specified in the test procedure. Such pressures need not exceed design pressure. Under such situations, after the equipment has withstood the pressure for required time it is recommended to reduce the pressure to the equipment design pressure before it is approached for a thorough inspection. However, this precaution is not applicable in the case of leak testing (for gasket joints) since the test pressure in this case will be normally less than design pressure.

e) Under similar safety precaution (new) equipment tested for integrity may be reduced to

2/3rd the test pressure before carrying-out close inspection. The reduced pressure so stated incidentally corresponds to the design pressure or slightly less than the design pressure.

f) On completion of hydraulic test, adequate venting shall be ensured before drainage.

This should be particularly taken care in the case of large thin vessels to prevent collapse.

OISD-128 _______________________________________________________________________________________

24

Annexure-III page 3 of 3

g) The specified test pressure includes the amount due to static head acting at any point under consideration. Particular care should be taken when applying a hydraulic test to a vertically mounted vessel, which may have been tested initially in the horizontal plane.

h) A point worth mentioning in this context refers to the precautions to be taken in case of

vessel supports fireproofed both from inside as well as outside. The internal condition of the supports needs to be ascertained prior to water filling, especially in case of equipment that have seen over 10 years of service. LPG spheres and some high-pressure vessels/columns (will be fire-proofed on both sides) are some equipment that come under this category.

i) For compartmented vessels, especially those with bellows, due attention shall be paid

to allowable internal pressure differences.

j) If a crack-propagation mechanism exists for the equipment, repeated pressure testing can cause the crack to grow. Care needs to be taken in this respect. e.g; this can include equipment in Amine, Caustic service etc and also equipment under cyclic loads – Pressure Swing Absorbers (PSA) etc. The “care” to be taken in this respect refers to pressure gradually applied as indicated in point ‘b’ above. However, care prior to pressure testing also has to taken by carrying-out suitable NDT for any other crack detection.

k) No vessel undergoing pressure testing shall be subjected to any form of shock loading.

e.g: hammer testing. 6.2 Pneumatic Testing

The consequences of failure during a pneumatic test can be devastating and such testing requires special precaution. Some of the precautions to be taken are as follows:

a) The equipment should be subjected to thorough testing including NDT as considered

necessary to ensure that there are no inherent defects / operating deterioration which may cause failure of the equipment during testing.

b) Except where it is necessary to meet design codes or statutory requirements, the test

pressure should be limited to 110% of design pressure for strength and to 100% of design pressure for leak testing. Pressure should be applied in small increments. As a practice of safety, equipment should not be subjected to pneumatic pressure beyond 1 kg/cm2g except for vessels/ piping systems that are specifically designed for pneumatic pressure and where water entry into the system is not tolerated due to operational reasons.

c) The pressure should be reduced to a pressure not exceeding design pressure before

any close examination is carried-out.

OISD-128 _______________________________________________________________________________________

25

Annexure-IV

CORROSION RATE AND REMAINING LIFE CALCULATION

The process/ procedure for Corrosion Rate calculation/ estimation shall be duly approved.

A. Remaining life of the pressure vessel shall be calculated as per the following procedure

Corrosion Rate = T (previous) – T (present) --------------------------------------- Time between present and previous inspections

T (previous) – Thickness reading taken during inspection

T (present) -- Thickness reading taken at present

Remaining life (Years) = T (actual) – T (minimum) ------------------------------------ Corrosion Rate

Where:

T (actual) = Actual minimum thickness

T (minimum) = Minimum required thickness as per applicable design code

B. For new pressure vessel and pressure vessels where service conditions are being changed, the probable corrosion rate for determination of remaining life shall be determined using following method;

i) Corrosion rate may be calculated from data collected on similar material and service

ii) If data on similar material or service is not available, then it can be estimated from published data

iii) If corrosion rate can not be established from above, the thickness determination shall

be made immediately after 3 months of service by thickness measurement. Subsequent measurements shall be made after appropriate intervals until corrosion rate is established.

OISD-128 _______________________________________________________________________________________

26

Annexure-IV

INSPECTION DOCUMENTATION CARDS (FORMS)

FORM 1

VESSEL DATA CARD

INFORMATION WEIGHTS DESIGN CODE_________________________ SHELL______________________________ MANUFACTURER_______________________ INTERNALS_________________________ MANUFACTURER’S INSULATION_________________________ ORDER NO.____________________________ DRG.NO.______________________________ EMPTY VESSEL______________________ JOB NO._______________________________ FULL OF WATER DIMENSIONS OPERATING CAPACITY________________ TOTAL HEIGHT________________________ MATERIALS HEIGHT BETWEEN TANGENTS__________ SHELL_________________________________ DIAMETER___________________________ HEADS_____________________________ WALL THICKNESS____________________ SKIRT_______________________________ TYPE OF HEADS______________________ BASE PLATE_________________________ CORR. BENCH MARKS_________________ MANWAY NOZZLE______________________

CONDITIONS

DESIGN TEMPOC_____________________ OPERATION TEMPO C_______________________ DESIGN PRESSURE KG/SQ.CM__________ OPERATING PRESSURE KG/SQ.CM____________ HYDROTEST PRESSURE KG/SQ.CM_____ CORROSION ALLOWANCE mm________________ STRESS RELIEVED____________________ RADIOGRAPHED____________________________ JOINT EFFICIENCY LONG SEAM________ HEAD_____________________________________

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FORM 4

DATA RECORD CARD

UNIT_________

INSP. POINT

DESCRIPTION SIZE SCHDL ORG. THICKN

RET. THICKN

YEAR WISE THICKNESS

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UJ+

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ANNEXURE-VI page 1 of 3

INSPECTION OF WELDING 1. DUTIES OF WELDING INSPECTOR

The duties of a welding inspector usually involve the performance of a number of operations, including:

i) Interpretation of drawings and specifications.

ii) Verification of the metal being welded.

iii) Verification of procedure and welder qualification.

iv) Checking application of approved welding procedures.

v) Verification of proper heat treatment.

vi) Assuring acceptable quality of welds.

vii) Preparation of records and reports.

2. INSPECTION PRIOR TO WELDING

i) The faces and edges of material should be examined for laminations, blisters, scabs and seams.

ii) Heavy scale, oxide films, grease, paint, oil and moisture should be removed.

iii) The pieces to be welded should be checked for size and shape. Warped, bent or

otherwise damaged material should be detected in the early stages of fabrication.

iv) Edge preparations, bevel angle, alignment of parts and fit up should be checked. The groove surface should be smooth (equivalent to machined/filled/ground surface). The root gap should be uniform.

v) Tacks to hold alignment of joint must be checked for soundness. Tacks which are to

be included in weld must be done by qualified welders in accordance with the welding procedure and must be of the same quality as root pass.

3. INSPECTION DURING WELDING

Visual inspection is employed to check details of the work while welding is in progress. The details to be considered are:

i) Welding process

ii) Cleaning.

iii) Preheat and interpass temperatures.

iv) Joint preparation.

v) Distortion control.

vi) Filler Metal.

vii) Interpass chipping, grinding or gouging.

The inspector should be thoroughly familiar with the items involved in the qualified welding procedures. Compliance with all details of the procedure should be verified. The root pass is most important from the point of view of weld soundness. The root pass may be checked by

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ANNEXURE-VI page 2 of 3 dye-penetrant testing. The inspection of root pass offers another opportunity to inspect for plate laminations.

In the case of double-groove welds, slag form the root pass on the side of the plate may from slag deposits on the other side. Such deposits should be chipped, ground or gouged out prior to welding the opposite side. Where slag removal is incomplete, it will remain in the root of the finished welds. Emphasis should be placed on the adequacy of the tack welds and clamps or braces used to maintain the root opening to assure penetration and alignment.

4. INSPECTION AFTER WELDING

Visual examination is the first stage in the inspection of a finished weld. The following quality factors should be checked:

i) Dimensional accuracy of the weldment (including distortion). ii) Conformity to specification requirements regarding extent, distribution, size, contour

and continuity of the welds. iii) Weld appearance, surface roughness, weld spatter etc. iv) Surface flaws, such as cracks, porosity, unfilled craters and crater cracks particularly

at the end of welds, undercutting, overlap, excessive weld reinforcement, excessive grinding etc.

v) The areas where fit-up lugs were attached or where handling lugs, machining blocks

or other temporary attachments were welded on, must be checked carefully after the attachment is removed. The area must be ground smooth and any pits or tears shall be filled in with weld metal ground smooth Air hardening materials should be preheated before any thermal cutting.

vi) Post-weld heat treatment time, temperature and heating/cooling rates. For groove

welds, the width of finished welds will fluctuate in accordance with the groove angle, root face, root opening and permissible tolerances. The height of reinforcement should be consistent with the specified requirements. Where not specified the inspector may have to rely on his judgement, guided by what he considers a good welding practice.

The finished weld should be thoroughly cleaned of oxides and slag for its final inspection.

After visual inspection the finished weld may be examined by one or more than one of the following techniques.

5. NON DESTRUCTIVE TESTS

i) DYE PENETRANT TESTING: Unless otherwise specified, the extent of this test will be 100% for all root runs for alloy steel welds. Adequate precautions as specified in applicable code should be taken while interrupting the welding cycle.

ii) MAGNETIC PARTICLE TESTING

iii) RADIOGRAPHY: Unless otherwise specified the extent of radiographic examination

will be as follows:

a) carbon and carbon molybdenum steels-10% of the welds.

b) alloy steel - 100% of the welds. The weld joint for radiography will be marked by the inspector.

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ANNEXURE-VI page 3 of 3 Radiographic examination of weld joints of two dissimilar materials shall be considered as per the higher metallurgy stipulations.

iv) ULTRASONIC TESTING.

v) EDDY CURRENT TESTING.

vi) FERRITE DETERMINATION.

vii) ULTRASONIC HARDNESS TESTING

Hardness testing by portable hardness testers may be considered as NDT method. Hydraulic testing may be done to check for leaks through welds, cracks etc.

6. DESTRUCTIVE TESTS

i) Mechanical tests like tensile, bend, impact, hardness, drift, flattening tests etc.

ii) Chemical analysis, microscopic examination, grain size determination etc.

The method and extent of examinations will be governed by applicable code requirements.

7. REPAIR OF WELDS

i) No repair should be carried out without prior permission of the inspector. ii) Weld discontinuities which are beyond acceptable limits shall be removed from the

joint completely by the process of chipping and grinding. iii) Where random radiography is specified, the first weld of each welder shall be

completely radiographed. In case of pipe size 150 mm dia. and below, the first two welds shall be completely radiographed.

iv) For each weld found unacceptable due to a welders fault two additional checks

should be carried out on welds performed by the same welder.

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Annexure-VII page 1 of 2

HYDROGEN BLISTERS-INSPECTION, EVALUATION AND REAPIR OF

PRESSURE VESSELS 1. INSPECTION

A. Visually inspect exterior and interior of vessel to determine location of all hydrogen blisters. B. Determine blister thickness by ultrasonic survey or by drilling. C. Conduct magnetic particle inspection at the edge and crown of any blister 2 inches and greater

in diameter to locate cracks which originate at, or have progressed near to the surface. D. In order to detect plate cracks (fissures), conduct magnetic particle inspection of the plate for a

distance of 6 inches beyond the limits of blisters 2 inches and greater in diameter appearing on the inside of the vessel. See Figure 1.

2. EVALUATION

A. If the blisters are clustered and originate at varying depths, replace the plate. B. If plate fissures are detected under Paragraph II. F, replace the affected plate. C. Hydrogen blisters visible in the cylindrical section of the shell, the crown of flanged and dished

or elliptical heads or in hemispherical heads and those that are away from seams of localised loading such as support pads should be considered acceptable.

D. Hydrogen blisters visible in and very near highly stressed areas such as head knuckles,

openings, seam and seam junctures, and support pads should be considered unacceptable in pressure vessels.

Affected components should be repaired or replaced following duly approved procedure.

E. If the diameter of any blisters listed in paragraph III.C exceeds the thickness of the plate, and

the vessel is operated below the metal transition temperature, the material should be replaced.

USE ASME Code, Section VIII Division 2, impact Test Exemption Curves for Carbon Steels.' as a measure of transition temperature.

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Annexure-VII page 2 of 2 3. REPAIRS

A. Cracked blisters on the outside surface of vessels in hydrofluoric acid service and cracked blisters on either inside or outside surfaces of vessels in other services shall be repaired as follows: 1. Drill 1/8" diameter holes at ends of each crown crack or edge crack to a depth equal to

blister depth as determined by thickness measurement.

B. Relieve hydrogen pressure in uncracked blisters 2 inches and larger in diameter by drilling a 1/16 inch diameter hole in the centre of the crown as follows:

1. Blisters showing on outside of vessels. a. Drill from outside. 2. Blisters showing on inside of vessel. a. Drill from inside. b. For vessels in hydrofluoric acid service, drill from outside. 3. Blisters showing on both inside and outside of vessel. a. Drill from inside. b.For vessels in hydrofluoric acid service, drill from outside surface only.

C. Vessels in hydrofluoric acid service.

1. If blisters 2 inches and larger in diameter on the inside surface have crown or edge cracks,

gouge out complete blister, fill with weld metal and grind smooth with plate surface.

2. If blisters on the outside surface are cracked, treat as in Paragraph III A.

D. Preheat, welding procedures, stress-relief, etc. should be in accordance with current acceptable practice for the specific vessel material.

E. Spheres and other vessels with tubular legs.

1. Hydrogen may diffuse through the vessel wall and become trapped inside tubular legs that

are welded to the vessel. This can form an explosive mixture with air in the legs.

2. Prior to any welding or cutting on or near the legs of a blistered vessel, the legs should be purged of any explosive gases as follows:

a) Drill 1/4" diameter holes at top and bottom of legs, with a non-sparking drill. b) Flush with inert gas or with air from the bottom hole.

3. Other dead spaces of significant volume should be treated in a similar manner.

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Annexure-VIII

INSPECTION TOOLS

Tools required for Pressure Vessels Inspection are as follows:

i) Ultrasonic Thickness Gauge.

ii) Ultrasonic Flaw Detector.

iii) Radiography Equipment.

iv) Magnetic Particle Testing Kit. (Wet Fluorescent Type)

v) Metallographic Equipment.Infra-red Scanner for Thermography.

vi) Dye Penetrant Kit.

vii) Paint Thickness Gauge.

viii) Shore Hardness Meter.

ix) Adhesion Testing Kit.

x) Holiday Detector.

xi) Spark Tester.

xii) Pit Depth Gauge.

xiii) ID & OD Gauges.

xiv) Plumb & Bob.

xv) Magnet.

xvi) Measuring Tape.

xvii) Magnifying Glass.

xviii)Temp. Indicating Crayons.

xix) Inspector’s Hammer.

xx) Straight Edge.

xxi) Safety Torch.

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Annexure-IX page 1 of 3

LIKELY LOCATIONS OF METAL WATAGE

A. MAIN FRACTIONATING TOWERS OF CRUDE DISTILLATION UNIT

The fractionating column bottom and internals are subjected to high temperature corrosion due to presence of sulphur whereas column top is prone to low temperature acidic corrosion because of salts and H2S present in the crude. The crude containing naphthenic acid also causes the corrosion of the column shell, and the same is pronounced in the sections where temperature ranges from 200oC to 400oC. Severity of naphthenic acid attack is higher where the turbulent conditions exist. The impingement plate particularly in the columns where the feed nozzle is radial is subjected to severe erosion. Noticeable corrosion or erosion is also generally observed where the steam impinges the shell. The dislodging of the trays (particularly valve trays) is common due to steam surge.

Galvanic corrosion is also observed at the location where cladded shells and uncladded shells join together. Where the lining is bulged, the parent metal is subjected to corrosion. Liquid level corrosion is noticeable in the top tray downcomer collectors particularly at the reflux collector trays.

B. CRUDE DISTILLATION UNIT- OVERHEAD ACCUMULATORS

Pronounced corrosion is generally noticed at the interface level of water and hydrocarbons. Mostly the corrosion is noticed in the bottom portion of the accumulators, which are not internally protected.

C. DEHYDRATOR, LP/HP SEPARATORS

Dehydrators & LP/HP separators of crude stabilising units are likely to get corroded in the bottom portion from 5 to 7 O’ clock position due to presence of salt & water.

D. VACUUM DISTILLATION COLUMNS

The sections where the turbulent conditions exist like impingement plate/flash zone are subjected to corrosion erosion due to naphthenic acid and sulphur in the crude. Columns, shells are also liable to corrode opposite to impingement plate due to rebound of fluid. Weldments and Heat Affected Zone are also susceptible to corrosion.

E. REACTORS IN REFORMERS

Generally the reactors are of low alloy steels like 2-1/4Cr-1 Mo or cladded with stainless steel. Due to this superior metallurgy metal wastage is generally not observed. However, the following locations give indication of deterioration/cracking.

i) Cracking of weldment of grid with shell at the bottom. ii) Baskets for collecting the catalyst dust are also prone to corrosion. iii) Liners installed in the big diameter nozzles are susceptible to bulging due to failure of weld

joints at the end. iv) Reactors made of low allow steel specially 2-1/4Cr-1 Mo are prone to temper embrittlement.

(Temper embrittlement is defined as a loss of ductility and notch toughness due to post weld heat treatment or high temperature service above 3700 C.)

F. REACTORS IN FCCU

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The shell, riser O.D. and portion of the cyclone dip leg O.D. are severely attacked in the riser extension type of installation. Where the grids are still used, erosion is found fairly uniform over most of the grid when high velocities are employed through cyclones. Some erosion occurs to

Annexure-IX page 2 of 3 the wall of the plenum chambers and to the top head where small plenums are in use. For those reactors with only two cyclones, high swirl of catalyst through the nozzles cause severe erosion.

The refractory lining generally stands up quite well in reactor cyclones. Normal repairs require some resurfacing of small areas or replacement of small localised sections. There are two kinds of valves at the bottom of dipleg. The one mostly in use is the flapper type with counter weight. The other is the trickle valve type, with the flapper plate hanging over the opening suspended by rings. The flapper type of valves are subjected to erosion.

G. REGENERATOR IN FCCU

In the plate type of distribution grid, erosion to the grid plates is a common phenomenon. Due to considerable vibration and heat differentials cracking of the grid plate can also take place.

In pipe type of grid design where seals are still in use, these seals may leak. Migration of catalyst past the seal could destroy a pipe grid in a very short time.

The branches (pipe coming off each lateral) experience metal loss, mainly to the top circumference. Occasionally the steam coming out of jet blowing directly into another branch, lateral or end plate creates erosion. Warpage of pipe grids can take place due to overheating during start-up and during operation. Many 5% Cr. grids experience weld cracking. The failure of refractory lining on the shell is another common problem. During operation, it may cause hot spots on the shell. Erosion of cyclone dip legs, failure of cyclone welds along with weld of cyclone supports may also take place.

H. ORIFICE CHAMBER IN FCCU

Erosion of the double disc sliding valve gates, erosion at the core near the inlet and at holes/sleeves in the grid plate are common problems. Bulging or cracking on the shell adjacent to the grid-plate also may take place. The erosion problems in orifice chamber are caused by the catalyst carryover from the Regenerator.

I. CHOKE CHAMBERS

Cracking of skirt and shell weld joints is quite common particularly in the coke chambers where the skirt is not of slotted type. In the coke chambers generally feed, stripping steam and water quench nozzles are installed at the bottom. Due to thermal cyclic shocks lower portion of the coke chamber gets bulged. At the advanced stages of bulging, circumferential welds which act as stiffeners get cracked in the axial direction. However, the effect is pronounced just opposite the feed entry nozzle at an elevation of about 1 meter. The chambers where the feed enters from the top, bulging is confined in the top portion. The conical portion of the coke chamber where the feed enters is also prone to cracking at the knuckle portion. Bottom flange to shell weld joint, weld joints of feed, water quench and steam nozzles are also likely to crack under thermal cyclic conditions.

J. BULLETS AND SPHERE

The corrosion and scaling is generally confined to the bottom between 5 to 7 O’ clock positions probably due to the presence of corrodents like H2S and water. LPG storage vessels are also prone to stress corrosion cracking. The circumferential weld joints below the equatorial plates in the LPG Horton spheres are more prone on such cracking.

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Annexure-IX page 3 of 3 K. VESSELS IN LOW TEMPERATURE SERVICE

Vessels in low temperature service e.g. in KTU of refineries and propane circuit of LPG recovery units of Gas Processing Plants are prone to external corrosion due to faulty insulation, which causes condensation of the vessels. The severity of corrosion increases in case of corrosive atmosphere as in KTU.

In these vessels internal corrosion due to moist So2 where condensation can take place, also occurs. Internals and shell are affected due to this.

L. AMMONIA STORAGE VESSELS

Generally the storage vessels are fabricated from Carbon steel and Nickel steels. For the operating conditions prevailing at refineries, material of construction used for Ammonia storage vessels in the refineries are carbon steels. The weld joints of C.S. vessels are prone to stress corrosion cracking particularly in the vessels, which have not been stress relieved initially or after fabrication repairs.

M. COLUMNS & VESSELS IN DIETHYL AMINE OR MONOETHYL AMINE SERVICE

The weld joints and heat affected zone of the columns and vessels in DEA and MEA service which have not been stress relieved are also prone to cracking due to presence of H2S or H2S and H2.

Further details about corrosion in pressure vessels are available in corrosion Manual-OISD Publication No. 136.

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