API653 Chap 4 Flashcards
When shall Roof plates need to be repaired or replaced? (2)
- avg thickness of less than 0.09” in any 100in^2
2. any holes through
What kind of inspection is needed for roof support members?
Distorted, corroded, and damaged members shall be evaluated and repair/replaced if necessary. (inspected for soundness by a method acceptable to the inspector)
API650 Appendix M used for?
operation temperature >200F , <500F
Should changers in operating condition on normal and emergency venting be considered?
Yes
Who should performed evaluation on the tank shell?
Storage tank engineer - shall conduct all anticipated loading conditions
what is controlling thickness (t2), and t1?
t2 = min thickness in a corroded area t1 = lowest average thickness
What min space measurement is needed over length L?
min of 5 equally spaced
What criteria to be used for continued operations for shell?
- t1>tmin + CA
2. t2> 60% of tmin + CA
When can scattered pits be ignored?
- no pit depth > (equal) to 1/2 tmin (excludes CA)
AND - sum of their dimension along any vertical line does not exceed 2” in an 8” length
What is tmin for a entire shell course?
tmin = 2.6(h-1)DG/SE
what is tmin for a local area shell?
tmin = 2.6(HDG)/SE
When is E = 1?
when weld or joints > 1” from corroded area
When is E = 1?
when weld or joints > 1” from corroded area , 6” away for riveted
Ht < H is possible? What to do if so?
Yes, owner should determine the consequence of operating the tank to H.
What to use on tanks D >200ft?
variable design point method
The formula considers only what?
Liquid loading only
The formula considers only what?
Liquid loading only
What is difference about the tmin formula for riveted tank shell?
E and S = 21000 if unknown
What is distortions?
- out of roundness
- buckled areas
- flat spots
- banding (horizontal)
- peaking (vertical joints)
What can cause distortions? (3)
- foundation settlement
2 over/under pressure - high wind.
Cracks in the shell to bottom weld must be removed?
Yes
When is API650 B.6 be considered?
elevated temp > 200F
What are some concrete deterioration? (5)
- calcining (loss of hydration) due to exposure of high temp
- deterioration of concrete exposed to underground water can be caused by chemical attack, cyclic changes in temp
- expansion of freezing moisture in porous concrete
- sulfate-type alkakies, chlorides can act corrosively to destroy the bond of concrete
- temperature cracks could result in access point for moisture
what to review for existing shell penetrations
- reinforcement,
- weld spacing,
- thickness of components
When are existing welds acceptable?
- when they are not modified or affected by repairs
AND - are closer than latest API 650 are acceptable for continued service IF the welds are examined by MT.
Existing tanks that were originally designed and constructed to the requirements of API 650, Appendix M, shall be evaluated for continued service, as follows
- S CANNOT exceed 0.8Y
- critical zone underground water cause , shell to bottom joints needs to be evaluated for elevated temp , liquid head and thermal cycles,
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)
- 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)].
- In addition, the maximum operating temperature shall not exceed the temperatures at which the tank
has operated successfully in the past
Conversion to Operation at Elevated Temperatures
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.
What to use to section to use to evaluate tank bottom settlement?
Annex B
causes of bottom failures (12)
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
Bottom plate thickness measurements NDE?
MFL + UT ( to confirm MFL)
Min thickness of bottom with no detection/containment?
0.1”
min thickness with containment/detection?
0.05”
reinforced lining > 0.05” , what is tmin of bottom?
0.05”
critical zone tmin?
smaller (1/2 t or 1/2 tmin of lower shell) but not less than 0.1”
projection of the bottom plate beyond the outside toe of the shell to bottom weld is
3/8”
How to calculate min annular bottom plate thickness
Stress = 2.34D(H-1)/t , and table 4.5
