API 653Tank Inspections with Susan Marie · PDF fileAPI 653 Inspection •In-Service Inspection •Foundation Settlement •Shell Inspection •Nozzle and Appurtenances •Roof Inspection

A P I 6 5 3 Ta n k I n s p e c t i o n sw i t h S u s a n M a r i e We n n e r

A P I 6 5 3 I n s p e c t i o n

• In-Service Inspection• Foundation Settlement

• Shell Inspection

• Nozzle and Appurtenances

• Roof Inspection

• Venting Assessment

• Out of Service Inspection• Bottom Assessment

• Internal Nozzle and Appurtenances

• Columns

• Internal Roof Inspection

A P I 6 5 3 I n - S e r v i c e I n s p e c t i o n

• Foundation Inspection• Does containment slope away from tank?

• Is tank adequately supported?



• Foundation Inspection• Is there significant wash out under the tank?

• Are there signs of tank bottom leakage?

• Is the tank chime corroding?


• Foundation Inspection• Is the tank grounded?

• Is the ground cable secured?


• Tank settlement can be visually detected…


• Foundation Settlement - Planar

READING

# FT. DEG

SHELL

(IN) Z U S

1 0 0 -1.00 -0.58 -0.42 -0.71

2 13.74 45.00 -0.50 -0.42 -0.08 0.12

3 27.49 90.00 -0.25 -0.27 0.02 -0.05

4 41.23 135.00 0.00 -0.22 0.22 0.19

5 54.98 180.00 -0.25 -0.29 0.04 0.08

6 68.72 225.00 -0.75 -0.46 -0.29 -0.24

7 82.47 270.00 -0.75 -0.61 -0.14 -0.33

8 96.21 315.00 0.00 -0.66 0.66 0.94


• Differential Settlement

API 653 requires a total of D/10 survey locations with a minimum of 8.

)(2

)11( 2

ExH

xYxLS

Where:

S = maximum permissible deflection inft

L = arc length between measurements points in ft

YS = yield strength in lbf/in2

E = Young’s modulus in lbf/in2

H = tank height in ft


• Shell Inspection• Visual Inspection

• Ultrasonic thickness measurement


• Shell Inspection• Minimum shell thickness

2.6 HDG

tmin =

SE

H = Height from bottom of shell course to maximum liquid level (feet)

D = Diameter of tank (feet)

G = Specific gravity of liquid

S = Maximum allowable stress in lb/in2 (Table 4.1)

E = Joint Efficiency (E = 1.0 for most situations)



• Shell Inspection• Acceptable measured values

t1 > tmin

t2 > 60% of tmin


• Shell Inspection• Widely scattered pits…

• If no single pit yields less than one half the minimum shell plate thickness

• Or the sum of the distances in a vertical line does not exceed 2” in 8” length


N o z z l e I n s p e c t i o n

• Shell Penetrations• Location and proximity to welds

• Size, shape and thickness of reinforcing pads

• Thickness of nozzles

P i p i n g c a n a f f e c t y o u r t a n k


• Windgirders need to be inspected for corrosion


• Roof Inspection• Plate thickness measurements

• Visual examination


• Roof Inspection• Is there evidence of structural

problems under the roof plates?


• Roof Inspection• Is there indications of water

pooling on the roof?

• Signs of top or bottom side corrosion resulting in penetration?


• Venting Assessment• Condition of normal vents…

• Are screens intact across all openings?

• Is emergency relief venting in place?

• Frangible Joint versus

• Vent penetrations

I s T h i s G o o d o r B a d ?

Ta n k V e n t i n g F a i l u r e

A P I 6 5 3 O u t o f S e r v i c e I n s p e c t i o n

• Out of Service Inspection• Bottom Assessment

• Foundation Settlement

• Shell Inspection

• Columns

• Roof Inspection

• Venting Assessment

W h y i s c l e a n i n g s o I m p o r t a n t

• “What an inspector cannot see cannot be effectively inspected.”

• The visual portion of the API Standard 653 inspection is critical.

• Additionally, items such as vacuum box, helium testing or other NDE methods can be severely limited without proper cleaning.

H o l e f o u n d v i s u a l l y f r o m g o o d s u r f a c e p r e p a r a t i o n

S S P C - S P 6

• “ A commercial blast cleaned surface, when viewed without magnification, shall be free of all visible oil, grease, dust, dirt mill scale, rust, coating, oxides, corrosion products, and other foreign matter, except for staining… Random staining limited…”

B l a s t C l e a n e d t o S P 6

S S P C - S P 1 4

• An industrial blast cleaned surface,… shall be free of all visible oil, grease, dust, and dirt. Traces of tightly adherent mill scale, rust, and coating residues are permitted…”

B l a s t C l e a n e d t o S P 1 4

O n c e C l e a n e d …

• Edge Settlement

• Bottom Settlement

• Bottom thickness measurement• Ultrasonic Thickness

• Tank Bottom Scan

E d g e S e t t l e m e n t

• Poor foundations can result in excessive edge settlement

E d g e S e t t l e m e n t

• API 653 Edge Settlement

38

I n t e r n a l S e t t l e m e n t

I n t e r n a l S e t t l e m e n t

Bottom Depressions Maximum permissible bottom

settlement or Bulges is given by:

BB = 0.37R

Where:

BB = maximum height of bulge or depth of local depression, in

R = radius of inscribed circle in bulged area or local depression, in ft

40

B o t t o m T h i c k n e s s M e a s u r e m e n t

• Ultrasonic thickness measurement

• Bottom plate scanning• Magnetic flux leakage

• Remote eddy current scan

• Ultrasonic floor scan

M a g n e t i c F l u x L e a k a g e ( M F L )

M a g n e t i c F l u x L e a k a g e ( M F L )

• The display depicts the strength of the field in the object

• At locations of metal loss, the screen will provide an alarm indication

• Once a suspect location is found, the inspector must follow up with UT to determine remaining metal thickness in the area

U T F o l l o w - u p

I s i t j u s t i n t e r n a l c o r r o s i o n ?

M i c r o b i o l o g i c a l l y I n d u c e d C o r r o s i o n

• MIC is a significant cause of internal corrosion in above and underground tanks

• Water and sludge collecting in the bottom of the tank is a perfect environment for bacteria growth

• Corrosion will typically be in the bottom low point of the tank

• There are several types of

bacteria that cause MIC

• Has a unique corrosion

pattern

M i c r o b i o l o g i c a l l y I n d u c e d C o r r o s i o n

• How do I recognize MIC?• Shape and texture of the corroded

area is typically rounded and undercut

• MIC Test Kits can be used to confirm MIC

B o t t o m P l a t e E v a l u a t i o n

• Minimum remaining thickness

MRT = RT – Or (stPr + UPpr)

MRT Minimum remaining thickness at the time of the next inspection

RT Measured remaining thickness after repairs

Or Operational interval between inspections

stPr Top-side corrosion rate

Upr Bottom-side corrosion rate

S u i t a b i l i t y f o r S e r v i c e

• Minimum floor plate thickness


• Shell Issues• Floating roof

• Gouging

• Corrosion where seals sit

• Standing water on bottom

• Vapor space corrosion dependent on product…

• Hydrogen grooving

• True general corrosion

• Buckling / dents

• Door sheets


• Shell Issues• Door sheets (API 653 9.2)

W h i l e i n s i d e …L o o k u p

• The columns must also be inspected.

• Plumpness

• Re-pad location / size

W h i l e i n s i d e …L o o k u p

• The interior of the roof structure must also be inspected.

• Holes in the tank shell and roof are visible from inside the tank

F l o a t i n g R o o f I n s p e c t i o n

• Visual inspection of seals

• Visual inspection inside of pontoons/chambers if steel

• Inspection of roof drain

• Inspection of access ladder

• Verify grounding


View A-A

Internal Floating Roof

Tank Shell

Annular Seal SpaceA A

Plan View

Tank Bottom

Tank Roof

Secondary Seal

Primary Seal

Floating Roof

Vapor Space

Liquid Product

See Detail

Possible Seal Gap Locations

Detail



B r i t t l e F r a c t u r e C o n s i d e r a t i o n

A s h l a n d O i l –F l o r e f f e , PA

• 3.8 million gallon diesel tank catastrophic failure

• Cause: brittle fracture in weld seams from reconstruction of tank.

• 750,000 gallons of diesel overflowed into Monongahela River

B r i t t l e F r a c t u r e C o n s i d e r a t i o n s


• Appendix C• Checklist for out of service

inspection…


• Limitations as written:• API 653 allows a wide range of

options that if not owner defined can result in significant differences in proposals and inspections

• API 653 focuses on the tank and foundation to the first flange. It does not include information on other appurtenances, electrical or piping systems

A P I 5 8 1 R B I I n s p e c t i o n E f f e c t i v e n e s s

Table 5.10 – Guidelines for Assigning Inspection Effectiveness – Tank Bottoms

Inspection

Category

Inspection

Effectiveness

Category

Soil Side Product Side

A Highly Effective

a. Floor scan 90+% & UT follow-up

b. Include welds if warranted from the

results on the plate scanning

c. Hand scan of the critical zone

Commercial blast

Effective supplementary light

Visual 100% (API 653)

Pit depth gauge

100% vacuum box testing of suspect welded joints

Coating or Liner:

a. Sponge test 100%

b. Adhesion test

c. Scrape test

B Usually Effective

a. Floor scan 50+% & UT follow-up

OR

a. EVA or other statistical method with

Floor scan follow-up if warranted by the

result

a. Brush blast

b. Effective supplementary light

c. Visual 100% (API 653)

d. Pit depth gauge

Coating or Liner:

a. Sponge test >75%

b. Adhesion test

c. Scrape test

C Fairly Effective

a. Floor scan 5-10+% plates; supplement

with scanning near Shell & UT follow-

up; Scan circle and X pattern

b. Progressively increase if damage found

during scanning

c. Helium/Argon test

d. Hammer test

e. Cut coupons

a. Broom swept

b. Effective supplementary light

c. Visual 100%

d. Pit depth gauge

Coating or Liner:

a. Sponge test 50 – 75%

b. Adhesion test

c. Scrape test

D Poorly Effectivea. Spot UT

b. Flood test

a. Broom swept

b. No effective supplementary lighting

c. Visual 25-50%

Coating or Liner:

Sponge test <50

E Ineffective None None

Questions?

Documents

API 653Tank Inspections with Susan Marie · PDF fileAPI 653 Inspection •In-Service Inspection •Foundation Settlement •Shell Inspection •Nozzle and Appurtenances •Roof Inspection