API653 Chap 4

Question 1

When shall Roof plates need to be repaired or replaced? (2)

Answer 1

1. avg thickness of less than 0.09” in any 100in^2

2. any holes through

Question 2

What kind of inspection is needed for roof support members?

Answer 2

Distorted, corroded, and damaged members shall be evaluated and repair/replaced if necessary. (inspected for soundness by a method acceptable to the inspector)

Question 3

API650 Appendix M used for?

Answer 3

operation temperature >200F , <500F

Question 4

Should changers in operating condition on normal and emergency venting be considered?

Answer 4

Yes

Question 5

Who should performed evaluation on the tank shell?

Answer 5

Storage tank engineer - shall conduct all anticipated loading conditions

Question 6

what is controlling thickness (t2), and t1?

Answer 6

t2 = min thickness in a corroded area
t1 = lowest average thickness

Question 7

What min space measurement is needed over length L?

Answer 7

min of 5 equally spaced

Question 8

What criteria to be used for continued operations for shell?

Answer 8

1. t1>tmin + CA

2. t2> 60% of tmin + CA

Question 9

When can scattered pits be ignored?

Answer 9

1. no pit depth > (equal) to 1/2 tmin (excludes CA)
   AND
2. sum of their dimension along any vertical line does not exceed 2” in an 8” length

Question 10

What is tmin for a entire shell course?

Answer 10

tmin = 2.6(h-1)DG/SE

Question 11

what is tmin for a local area shell?

Answer 11

tmin = 2.6(HDG)/SE

Question 12

When is E = 1?

Answer 12

when weld or joints > 1” from corroded area

Question 13

When is E = 1?

Answer 13

when weld or joints > 1” from corroded area , 6” away for riveted

Question 14

Ht < H is possible? What to do if so?

Answer 14

Yes, owner should determine the consequence of operating the tank to H.

Question 15

What to use on tanks D >200ft?

Answer 15

variable design point method

Question 16

The formula considers only what?

Answer 16

Liquid loading only

Question 17

The formula considers only what?

Answer 17

Liquid loading only

Question 18

What is difference about the tmin formula for riveted tank shell?

Answer 18

E and S = 21000 if unknown

Question 19

What is distortions?

Answer 19

1. out of roundness
2. buckled areas
3. flat spots
4. banding (horizontal)
5. peaking (vertical joints)

Question 20

What can cause distortions? (3)

Answer 20

1. foundation settlement
   2 over/under pressure
2. high wind.

Question 21

Cracks in the shell to bottom weld must be removed?

Answer 21

Yes

Question 22

When is API650 B.6 be considered?

Answer 22

elevated temp > 200F

Question 23

What are some concrete deterioration? (5)

Answer 23

1. calcining (loss of hydration) due to exposure of high temp
2. deterioration of concrete exposed to underground water can be caused by chemical attack, cyclic changes in temp
3. expansion of freezing moisture in porous concrete
4. sulfate-type alkakies, chlorides can act corrosively to destroy the bond of concrete
5. temperature cracks could result in access point for moisture

Question 24

what to review for existing shell penetrations

Answer 24

1. reinforcement,
2. weld spacing,
3. thickness of components

Question 25

When are existing welds acceptable?

Answer 25

1. when they are not modified or affected by repairs AND 2. are closer than latest API 650 are acceptable for continued service IF the welds are examined by MT.

Question 26

Existing tanks that were originally designed and constructed to the requirements of API 650, Appendix M, shall be evaluated for continued service, as follows

Answer 26

1. S CANNOT exceed 0.8Y 2. critical zone underground water cause , shell to bottom joints needs to be evaluated for elevated temp , liquid head and thermal cycles,

Question 27

Existing elevated temperature service tanks that were not originally designed and constructed to the requirements of API 650, Appendix M, but have a successful service history of operation shall be evaluated for continued service as noted ..(2)

Answer 27

1. If the tank diameter exceeds 100 ft and the tank was not constructed with a butt-welded annular ring, an analysis of the critical zone is required [see 4.3.10.1.1 b)]. 2. In addition, the maximum operating temperature shall not exceed the temperatures at which the tank has operated successfully in the past

Question 28

Conversion to Operation at Elevated Temperatures

Answer 28

a) The allowable shell stresses of this standard (API 653) shall not be used. b) The need for a butt-welded annular ring shall be determined in conformance with API 650, Appendix M and installed if required. c) The shell-to-bottom joint shall be evaluated for fatigue conditions.

Question 29

What to use to section to use to evaluate tank bottom settlement?

Answer 29

Annex B

Question 30

causes of bottom failures (12)

Answer 30

a) internal pitting and pitting rates in the anticipated service; b) corrosion of weld joints (weld and heat affected zone); c) weld joint cracking history; d) stresses placed on the bottom plates by roof support loads and shell settlement; e) underside corrosion (normally in the form of pitting); f) inadequate drainage resulting in surface water flowing under the tank bottom; g) the lack of an annular plate ring when required; h) uneven settlement that results in high localized stresses in the bottom plates; i) roof support columns or other supports welded to the tank bottom where adequate allowance for movement was not made; j) rock or gravel foundation pads with inadequately filled-in surface voids; k) nonhomogeneous fill under the tank bottom (e.g. A lump of clay in a sand foundation pad); l) inadequately supported sumps

Question 31

Bottom plate thickness measurements NDE?

Answer 31

MFL + UT ( to confirm MFL)

Question 32

Min thickness of bottom with no detection/containment?

Answer 32

0.1"

Question 33

min thickness with containment/detection?

Answer 33

0.05"

Question 34

reinforced lining > 0.05" , what is tmin of bottom?

Answer 34

0.05"

Question 35

critical zone tmin?

Answer 35

smaller (1/2 t or 1/2 tmin of lower shell) but not less than 0.1"

Question 36

projection of the bottom plate beyond the outside toe of the shell to bottom weld is

Answer 36

3/8"

Question 37

How to calculate min annular bottom plate thickness

Answer 37

Stress = 2.34D(H-1)/t , and table 4.5