Table of Contents

1 Scope 2

2 Purpose 2

3 Safety 2

4 References 2

5 Inspection Guidelines 4

6 Detailed Inspection Guidelines 5

1 Scope This procedure guidelines for inspecting above ground storage tanks that

have been placed in service.

2 Purpose This procedure to assist the API Inspectors of Tank Inspection Units in

their selection by providing Typical Plans and inspection checklist for

all types of existing storage tank, on stream evaluation, and tracking of

existing equipment condition.

3 Safety 3.1 Radiographic examination personnel safety should be per general

industrial standard and that of specific industry requisite.

3.2 All pressure testing should be in compliance with guidelines

established by the company and that of the concerned industry’s safety

guide lines.

3.3 Use of personnel protection equipment and safe entry for inspection is

the responsibility of the inspector/Inspection Engineer

4 References The following standards were used in the preparation of these inspection

guidelines and should be carefully reviewed by the inspectors/inspection

engineers prior to performing inspection. All references should be the

latest issued revision or edition.

American Society of Mechanical Engineers

ASME SEC V Nondestructive Examination

ASME SEC VIII Boiler and Pressure Vessel Code

American Petroleum Institute API STD 510 Pressure Vessel Inspection Code

API RP 571 Damage Mechanism Affecting fixed Equipment

API RP 580 Risk Based Inspection

API RP 578 Material Verification

API STD 620 Design and construction of Large, Welded, Low Pressure

Storage Tanks

API STD 650 Welded Steel Tanks for Storage

API STD 653 Tank Inspection, Repair, Alteration and Reconstruction

NBIC National Board Inspection Code

5 Inspection Guidelines These guidelines are intended for inspectors and inspection engineers.

Generally, the steps for storage Tank inspection are shown in the

Flowchart in attachment-A. Equipment shall be inspected per Typical

Inspection Plan (TIP) and Checklist (detailed check list of API 653 shall

be the guide) shown in attachment B and C respectively.

5.1 Check the tank drawing, construction codes, and material of

construction, internal parts, and dimensions (diameter, height and

thickness).

5.2 Read the tank file and note history of corrosion, repairs and

replacement if any.

5.3 Carry out joint inspection (check includes ventilation, blinds, scaffolds

and lighting) and obtain entry permit to ensure the Tank is safe to enter

and inspect. At the time of inspection keep a man watch for your safety.

5.4 Primarily carry out external inspection for external leaks, external

damage, insulation or paint damage, external corrosion.

5.5 Ensure the tank is isolated with proper blinds. Obtain entry permit from

operation. Prior to internal inspection entry gas test to make sure no toxic

gases are released. While entry to the tank, have a man stand by at the

man way for personnel safety and company loss prevention.

5.6 Start preliminary inspection at all man ways (man way inspection)

going from bottom (all around) to the top. Record the observations on a

note pad at each level. Start entering the tank from the bottom man

way and assess the conditions of nozzles, tank bottom plates,

tank shell plates, tank internal hardware’s (Columns, float,

supports / legs, sumps, etc.). Identify each item and note the

observations for your inspection evaluation.

6 Detailed Inspection Guidelines

While performing detailed inspection look for pitting corrosion,

erosion/corrosion, channeling, weld erosion/corrosion and cracks,

mechanical damages while opening and closing, environmental cracking,

bulging and blistering and the like are some that will be noted with in the

tanks. Coating conditions, if coated. A good cleaning and careful

evaluation will help make a good decision. Sometime Fitness for

Service inspection (FFS) assessment will be required and full

evaluation will have to be done from design, operation, and history of

operation to increase the service life of the tank.

6.1 Actual Thickness Determination of shell and shell penetrations

6.1.1 A general UT thickness survey of a tank shell will typically require a

grid system as noted below. (Shell thickness gauging shall preferably be

done by remote controlled UT crawler machines.)

a, Mark vertical lines from the reference points at the bottom of

shell to the top of shell. Number of reference points around circumference

is 8,12,16,20 and 24 for tank diameters less than 12 meters, between 12

and 20 meters, between 21 and 27 meters, between 28 and 36 meters, 36

meters and above, respectively.

b, Mark two horizontal grid lines on each shell course, the first one

at 300 mm above the lower edge of each course, and the second one at

mid-height of each course. Number horizontal grid lines 01, 02, 03 etc.

starting with 01 at 300 mm above tank bottom.

c, In areas of significant external pitting, the depth should be

measured with a pit gauge and subtracted from the shell thickness

adjacent to the pit, to obtain the remaining thickness at the bottom of the

pit. Visual inspection is to be carried out to locate locally corroded and

pitted areas prior to ultrasonic gauging

d, Ultrasonic thickness readings shall be taken at the intersection of

vertical and horizontal grid lines.

e, Ultrasonic thickness measurements of nozzles and man way

neck plates should be taken as close as possible to the reinforcing or shell

plate at 12, 3, 6 and 9 O’clock positions.

6.1.2 The amount of inspection can be increased further, if appropriate,

based on the initial evaluation results.

6.1.4 At any location where readings are less than 90% of original

thickness or thinning is equal to or more than 1 mm from the original

thickness, the adjacent area shall be UT scanned to determine the extent

of corrosion.

6.2 Condition Determination of Tank bottom

6.2.1 During inspection, the entire floor should be visually examined

for holes, cracked welds, and any areas that were previously

repaired.

6.2.2 Bottom plate UT thickness readings shall be taken at least as

detailed below

a, MFL shall be made over the entire bottom plates to identify

thinned areas

b, Carry out hand scan or UT scanning on all inaccessible areas

c, Perform UT follow up or back up.

6.2.3 Bottom plates and bottom sump shall be 100% vacuum tested for all

weld joints including shell to bottom joints.

6.2.4 UT scanning shall be performed for Tank Sump.

6.2.5 MPI shall be performed at shell to annular plate joints.

6.3 Condition Determination of Tank Roof

6.3.1 Visual checks will locate areas of especially severe corrosion, such

as at depressions in the roof surface, areas around roof support sleeves,

near roof drains and vents, and similar locations where water can

accumulate. Badly corroded areas of the roof should be examined for

evidence of leaks. The condition of the paint on the roof will provide

a good indication of any potential roof corrosion problem. Weathering

of the paint system is more severe on the roof due to its

exposure to sunlight and the presence of pools of water.

6.3.2 The underside of the roof should be checked for corrosion.

Ultrasonic thickness measurements should then be made to determine

the rate of corrosion. The external face of the pontoon in the

region of the liquid level should be inspected for grooving,

pitting, and corrosion because this area is prone to corrosion due to the

liquid-vapor interface.

6.3.3 Floating roof UT reading shall be taken as a minimum as detailed

below; (the spots required in check list can’t be substituted with the

following requirement)

Ultrasonic thickness measurements should be performed along the

extension of the Vertical grid lines at 200mm from shell, at 2/3

radius and at 1/3 radius. In addition thickness measurement must

be taken at locations where significant external and internal

corrosion are observed.

OR

Rectangular plates- 6 readings per plate

Sketch Plates- 3 readings per plate

10 additional readings between shell and gauge.

6.4 Determining the Tank Settlement

Shell and bottom settlement must be evaluated as part of the tank

inspection activity to determine if any corrective action is required.

6.4 After completion of the full inspection, request any other needs for

cleaning or removal and cleaning of internals for detail inspection and

repairs or renewal if any.

6.5 Follow up the recommendations and the related repairs per standards,

the codes, ASME and API. Carry out the final inspection on completion

of the repairs and cleaning as applicable.

6.6 Applicable standards and codes: ASME SEC VIII D1, API STD 650,

and API STD 653.