API 653 Fitness-for-Service & Repair 5 — Questions and Answers
Question 1: According to API 653, when is a full hydrostatic test NOT required after a repair?
- When only the roof structure (not shell) is repaired and no new penetrations are added (Correct answer)
- When the repair involves any shell weld
- When the tank stores water
- When the repair is done by a certified contractor
Correct answer: When only the roof structure (not shell) is repaired and no new penetrations are added
API 653 permits waiving the hydrostatic test for roof-only structural repairs that do not involve new penetrations, provided other specified inspections are completed.
Question 2: A tank shell course shows widespread pitting with the deepest pit measuring 40% metal loss. The average metal loss over a 2-inch diameter area is 25%. Per API 653 simplified FFS criteria, this area is:
- Acceptable because average loss is below 33%
- Unacceptable because any pit exceeding 30% requires repair
- Evaluated using both maximum pit depth and average area criteria to determine acceptability (Correct answer)
- Acceptable only if a coating is applied over the pitted area
Correct answer: Evaluated using both maximum pit depth and average area criteria to determine acceptability
API 653 FFS assessment uses both the maximum pit depth criterion and the average thickness criterion over the assessment area, and both must be satisfied.
Question 3: Which of the following tank conditions is specifically addressed by API 653's external floating roof fitness-for-service criteria?
- Pontoon corrosion that compromises buoyancy (Correct answer)
- Corrosion of the fixed roof structural rafters
- Settlement-induced damage to the foundation ring wall
- Leakage from the shell manway gasket
Correct answer: Pontoon corrosion that compromises buoyancy
API 653 includes criteria for evaluating pontoon corrosion on external floating roofs because buoyancy loss leads to sinking and potential product loss.
Question 4: When API 653 refers to 'temporary repairs,' which statement is most accurate?
- Temporary repairs are never permitted on API 653 tanks
- Temporary repairs such as clamps or plugs may be used but require a plan for permanent repair within a defined timeframe (Correct answer)
- Temporary repairs extend the next internal inspection interval by 5 years
- Temporary repairs require the same documentation as permanent repairs plus a hydrostatic test
Correct answer: Temporary repairs such as clamps or plugs may be used but require a plan for permanent repair within a defined timeframe
API 653 allows temporary repairs as a short-term measure provided there is an engineering basis for their use and a plan for permanent repair is established.
Question 5: For the purpose of API 653 fitness-for-service calculations, what value of specific gravity (SG) is used when the stored product SG is unknown?
- SG = 0.8 (light hydrocarbon)
- SG = 1.0 (water) (Correct answer)
- SG = 1.4 (brine equivalent)
- SG = 0.7 (minimum API gravity product)
Correct answer: SG = 1.0 (water)
When the stored product specific gravity is unknown, API 653 uses SG = 1.0 (water) as a conservative default for minimum thickness calculations.
Question 6: Which API 653 provision governs the acceptability of a repaired area where the new weld reinforcement height exceeds the code limit?
- The excess reinforcement is always acceptable if the weld passes visual inspection
- Excess weld reinforcement must be removed by grinding to comply with API 653 limits (Correct answer)
- The weld must be radiographed but the excess height is otherwise acceptable
- The area must be stress-relieved post-weld heat treated
Correct answer: Excess weld reinforcement must be removed by grinding to comply with API 653 limits
API 653 specifies maximum weld reinforcement heights, and any excess must be ground flush to meet code limits and avoid stress concentration.
Question 7: Under API 653, what action is required when the calculated next inspection date has passed and the tank remains in service?
- Continue operating until the next scheduled shutdown, then inspect
- Immediately shut down the tank until inspection is complete
- Perform an engineering review to justify continued operation and establish a new inspection schedule (Correct answer)
- Apply a conservative 20% reduction to the operating level as mitigation
Correct answer: Perform an engineering review to justify continued operation and establish a new inspection schedule
API 653 requires an engineering review with documented justification when an inspection interval has been exceeded, to establish a revised schedule and confirm continued fitness for service.
API 653 Fitness-for-Service & Repair 5
According to API 653, when is a full hydrostatic test NOT required after a repair?