Definitions
Repair
Work necessary to maintain or restore a tank to a condition suitable for safe operations.
What are some common causes for bottom failure.
A) internal pitting
B) corrosion of welds
C) weld joint cracking history
D) the lack of an annular plate ring when required.
E) underside corrosion (normally in the form of pitting)
Nozzles for hot taps are limited to what maximum diameter.
4 inch NPS
The tank shall be _____ and _______ prior to commencement of dismantling.
Cleaned, Gas-freed
NDE shall be preformed in accordance with? (code and section)
API 650 section 8
As-built standard
The standard (such as API standard or UL Standard) used for the construction of the tank component in question.
When the results of a tank inspection show that a change has occurred from the original physical condition of that tank, an _______ shall be made to determine its ________ for continued use.
Evaluation, Suitability
Welded-on patch plates over existing patches are not allowed in the _______________.
Critical zone.
When should piece markings be done.
Prior to dismantling for ready identification and placement when tank is reconstructed
Cavities resulting from gouging or grinding operations to remove weld defects shall be examined by the
magnetic particle or liquid penetrant method
Break-over point
The area on a tank bottom where settlement begins.
Tank roof evaluation- roof plates corroded to an average thickness of less than___ in any _____ area or roof plates with any holes through the roof plate shell be repaired or replaced.
0.09in, 100in sq
What is the minimum dimension for a replacement shell plate
12 inches or 12 times the thickness of the replacement plate, whichever is greater.
when cutting alongside of remaining welds during dismantling of a tank, what is the minimum distance from the remaining weld that must be maintained.
2 inches
bottom plate repairs can be tested using what methods.
magnetic particle, vacuum box and solution, or tracer gas and detector.
Candidate Tank
The tank(s) for which the corrosion rates are not known.
What are the principal causes of foundation failure.
Settlement, erosion, cracking, and distortion of concrete.
the maximum and minimum repair plate dimensions using lap-welded patch plates.
48 inches by 72 inches, with a minimum of 4 inches.
what is the minimum number of matching center punch marks are required on shell plate to facilitate alignment for reconstruction.
two sets
When is a Hydrostatic testing, held for 24 hours shall be performed
on a reconstructed tank, any tank that has undergone major repairs or major alterations, a tank where an engineering evaluation indicates the need for a hydrostatic test due to an increase in the severity of service.
Control tank
The tank(s) for which the corrosion rates and service history are known and documented.
Widely scattered pitting may be ignored if?
A) no pit depth results in the remaining shell thickness being less than 1/2 the minimum acceptable tank shell thickness exclusive of corrosion allowance
B) The sum of their dimensions along any vertical line does not exceed 2in. in an 8in length.
when repairing a tank floor a patch-plate may be smaller than 12 inches if it meets what criteria
It is equal to or exceeds 6 inches in diameter; it does not overlap a bottom seam; it is not placed fully or partially over an existing patch; and it extends beyond the corroded bottom area, if any, by at least 2 inches.
What is the tank Radii tolerance for a tank that is 200ft in diameter.
+ or - 1 inch
Stress in a repaired area shall not exceed _____ lbf/in sq
7000