BSR Inspection Case Study - Cyclone

8/11/2019 BSR Inspection Case Study - Cyclone

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Case Study -2nd Regenerator Secondary Cyclones.

Prepared By

Mr. Tran Anh Vu

Deputy Technical Manager

1. Summary

2. Drawing3. History

4. Observation/ Findings

5. Root Cause Analysis

6. Recommendation

7. Repair Method

8. Lesson Learnt

CONTENTS

The RFCC unit was shut down for 2nd TA in 2014. During

inspection secondary cyclone CY-1504 E~H in the 2nd

regenerator D-1503 were found severe damaged. The carbon

steel portion in the cyclone barrel were replaced with SS-304H

material after detail analysis of root cause for damages by

performing NDT methods like UTM, Hardness test, replica etc.

Summary Drawing


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Drawing

refractory crack

refractory crack

History

In 1st TA, some crack were found in the refractory around the carbon steel

portion of cyclone barrel

BeforeHacking

AfterHackingBracingBowing

Observation/ Findings (TA 2014)

Picture 2

refractorycrack

BeforeHacking

refractorycrack

Observation/ Findings

Licenser Design Detail design & Actual

LicensorDesign Detail design &Actual

Dis-similar weld joint is slanting and near

to 2nd regenerator shell

Dis-similar weld joint is horizontal and

far away from 2nd regenerator shell

Have extrenal refractory to cover

dis-similar weld

125mm thick refractory outside the

carbon steel material

In cyclone barrel less carbon steel andmore SS material inside re-regenerator

In cyclone more carbon steel and lessSS material inside re-generator


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Dis-similar

weld joint


Picture 4 shows degradation/metal flakes in cyclone barrel (Carbon

Steel portion). For all 4 cyclones same condition


CycloneF

Dissimilar weld metal found crack in the heat affected zone of carbon steel

portion in two cyclones E &F.

CycloneE


Picture 6b show horizontal Stiffener bracing found bend(Bowing) at

middle of bracing & Picture 6a show crack in one of the dipleg weld

metal

Picture 6a Picture 6b


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UTM:38.8 H:115UTM:38.78H106

H131

Philosophy

NDT inspection is carried out based on the API 579

Fitness for service philosophy.For Assessment of fire damage chapter 11 fig: 11.7.

NDT inspection are carried out step by step process

First perform Hardness test to evaluate the hardness

limit. If hardness limit is lower 240HB that means

the metal is good

If the hardness value is higher than 240 HB check the

microstructure and follow subsequent test as per flowchart.

UTM:38.8 H:115UTM:38.78H106

H131

Philosophy

UTM:38.8 H:115UTM:38.78H106

H131


NDT- UTM ResultUTM result confirms there is no major thickness

reduction. From the dis-similar weld zone to about 0.6

meter in height towards Carbon Steel cannot measure the

thickness due to high flaking of material and above 0.6

meter For all four cyclones the similar condition.

Picture 1 shows the thickness near the dis-similar weld

seam is reduced about 3-4mm.

Picture 1

UTM:38.8 H:115UTM:38.78H106

H131


NDT- Hardness Result

Hardness test result confirms that from the dis-

similar weld zone to about 0.7-0.9 meter in heighttowards Carbon Steel the hardness value is very high

around 600HB and many locations cannot measure

hardness due to flaking. Above 0.9 meter the

hardness value is with in the acceptable range. All

four cyclones has the similar condition.


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UTM:38.8 H:115UTM:38.78H106

UTM:39.8 H:488

H131


NDT- Replica Result

Replica result says that Carbon steel material in the

cyclone has undergone many damage mechanism like

creep voids, degraded microstructure, no carbide have

only ferrite, high temperature sulfidation, graphitation

and microstructure degradation due to high temperature

corrosion etc

UTM:38.8 H:115UTM:38.78H106

UTM:39.8 H:488

H131


NDT- Replica Result

Cyclone H replica result says the Carbon steel material about 0.7 m above dis-similar

weld joint has creep voids and degraded microstructure

Report 3

CY 1504-E

Cyclone E replica result by PVI and Vietnam Material Institute says the Carbon steel

material near the dis-similar weld zone is no carbide have only ferrite

Report 4

UTM:38.8 H:115UTM:38.78H106

UTM:39.8

H:

488

H131


NDT- Replica Result

Cyclone E replica result says the Carbon steel material about 0.5 m above

dis-similar weld joint was damaged due to high temperature sulfidation, graphitation and

microstructure degradation. Even after remove 5mm of degraded carbon steel material the

replica result shows that the material microstructure structure is decomposed

Report 5


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Cyclone G replica result says the Carbon steel material about 0.6 m above

dis-similar weld joint was damaged due to high temperature sulfidation,

Report 6 CY 1504-F

Cyclone F replica result says the Carbon steel material about 0.3 m above

dis-similar weld joint was partially degraded microstructure due to high

temperature corrosion

Report 7

UTM:38.8 H:115UTM:38.78H106

H131


Metal Laboratory Analysis result

The flaking metal portion was detailed analyzed in the laboratory, the

results says that this is the corrosion product, which is iron oxide, a

product of metal oxidation at high temperature.

The laboratory report says the cause for corrosion at cyclone is due to the

damage refractory. Oxygen has contacted with metal surface through the

defect positions which led to chemical corrosion at high temperature.

The corrosion products are iron oxides under the form of magnetite

(Fe3O4) and hematite (-Fe2O3).

UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis

Replica result for CY-1504H microstructure @400X shows the

isolated creep void.

API 571, clause 4.2.8.3 point a says the rate of creep deformation is

a function of the material, load, and temperature.

API 571, clause 4.2.8 Table 4-2 says Threshold Temperatures for

Creep for Carbon steel material is 370C

API 571, clause 4.2.8.3 point b says If the metal temperature exceeds

threshold temperature values, then creep damage and creep cracking

can occur

Creep Damage


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UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis

JGC Heat Transfer Analysis

UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis


UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis


UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis



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UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis


UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis


UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis


UTM:38.8 H:115UTM:38.78H106

H131

Root Cause Analysis



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UTM:38.8 H:115UTM:38.78H106

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RecommendationAPI 571 clause 4.2.8.6 point c says Creep damage is not reversible.

Once damage or cracking is detected much of the life of the

component has been used up and typically the options are to repair or

replace the damaged component.

ASM Volume 17 Table 2, creep classification table says for fewcavities of creep damage need to re-inspect after 20,000hrs (less than

3 years estimated next Turn around)

API 579 chapter 11 figure:11.7 says if hardness value high,

microstructure is unacceptable, decarburized the material need to be

replaced

The laboratory sample test reports shows the Carbon steel metal was degraded due to high

temperature oxidation. Referring to the above table (API-571) based on the current

operation temperature of D-1503 the corrosion rate will be severe above 48 mils/year or

1.21 mm/year. As per design the allowable corrosion allowance is 1.5 mm for CS and

0.75mm for SS. This corrosion allowance is calculated for 25mm thickness of cyclone

barrel CS material.

Root Cause Analysis

Key Factors Recommendation

6. Project specification 8474L-000-JSS-6300-001 Rev-2 Clause 7.4.1 mention

requirement for minimum weld distance is 100mm or 2T:

Recommendation for Repair method

Option 1: Replacement (Permanent repair) as licenser design

The SS304H material can withstand the high temperature corrosion like

sulfidation, graphitization, oxidation etc.

Key factors recommendation should be considered in this option 1.

Option 2: PatchingAPI 510 calls th is option 2 method as temporary method:Temporary repairs should be removed and replaced with suitable permanent repairs at

the next available maintenance opportunity.

Temporary repairs may remain in place for a longer period of time only if evaluated,

approved, and documented by the engineer and inspector.


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RecommendationOption 2: Patching

Limitation for fillet welding patch

Fillet-welded Patches

Fillet-welded patches may be used to make temporary repairs to damaged, corroded,

or eroded areas of pressure vessel components.

This type of patch cannot control crack during opportunity maintenance

As per ASME PCC-2 calls:

i. Differential thermal expansion between the cyclone shell and the reinforcing

lap band sleeve shall be considered in the design and application of sleeves.

ii. Fillet welded patch repair is allowed up to 345C only. So the refractory

work shall make sure the temperature of CS is not over 345C

iii. ASME PCC2 clause 3.5 call The fillet weld patch thickness should be 1.4

times the carrier steel

7/31/2014

Repair

After Cyclone barrel cutting New Cyclone barrel

7/31/2014

Repair

After new Cyclone barrel welding After completion of welding

When Carbon steel material is operating under creep range

for long period it undergoes multiple damage mechanisms.

Replica shall be done to analysis the microstructure. Fitness

for service should be followed to assess the damage.

The dis-similar welding should be monitored closely at the

every possible opportunity . When operating temperature is

high Nickel chrome filler wire should be used rather than

E-309 filler wire

7/31/2014

Lesson Learnt

BSR Inspection Case Study - Cyclone

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