API 653 Repair and Alteration 3 — Questions and Answers
Question 1: Per API 653, what is required before welding a repair patch on a tank that has contained flammable product?
- Pressure test of the repair area
- Gas freeing and atmosphere testing to safe levels (Correct answer)
- Coating the interior with fire-resistant paint
- Filling the tank with water to the repair location
Correct answer: Gas freeing and atmosphere testing to safe levels
API 653 mandates that tanks be gas-freed and tested to confirm safe atmospheric conditions before any hot work such as welding.
Question 2: According to API 653, what is a 'major repair' compared to a 'minor repair' in the context of aboveground storage tanks?
- Any repair costing more than $10,000
- A repair that restores the original design condition versus one that does not affect design function (Correct answer)
- A repair requiring complete draining versus one performed in service
- A repair involving welding versus one using mechanical fasteners
Correct answer: A repair that restores the original design condition versus one that does not affect design function
API 653 classifies major repairs as those that restore original design intent or structural integrity, distinguishing them from maintenance-level minor repairs.
Question 3: When a tank bottom is repaired by installing a new bottom over the old one (lap-over-bottom), what is the minimum lap dimension per API 653?
- 1 inch (Correct answer)
- 2 inches
- 3 inches
- 4 inches
Correct answer: 1 inch
API 653 requires a minimum 1-inch lap when installing a new tank bottom over the existing corroded bottom.
Question 4: In API 653, what must be done when a repaired or altered tank is returned to service with a reduced maximum allowable working level (MAWL)?
- The reduction must be documented and the tank must be marked with the new MAWL (Correct answer)
- A new API 650 tank must be constructed
- The owner must obtain a variance from the state
- The reduction only applies during the first year after repair
Correct answer: The reduction must be documented and the tank must be marked with the new MAWL
API 653 requires that any MAWL reduction be documented in the tank record and physically marked on the tank to prevent overfilling.
Question 5: Which welding process is generally NOT acceptable per API 653 for structural repairs to tank shells without additional qualification?
- Shielded Metal Arc Welding (SMAW)
- Submerged Arc Welding (SAW)
- Flux Core Arc Welding (FCAW)
- Stud welding for structural attachments (Correct answer)
Correct answer: Stud welding for structural attachments
Stud welding is not a recognized structural welding process for load-bearing repairs under API 653 without specific qualification and engineering approval.
Question 6: Per API 653, when must a post-weld heat treatment (PWHT) be performed on a repaired tank shell?
- After every weld repair regardless of material or thickness
- When required by the original construction code or when thickness exceeds specified limits for the material (Correct answer)
- Only when the tank stores caustic or hydrogen service products
- PWHT is never required for storage tank repairs
Correct answer: When required by the original construction code or when thickness exceeds specified limits for the material
API 653 requires PWHT when mandated by the applicable construction code or when material thickness and chemistry exceed the limits that exempt repairs from PWHT.
Question 7: A tank undergoing repair has a shell-to-bottom weld that is deteriorated. According to API 653, what action is required before repairing this weld?
- The tank must be completely empty and gas-free
- The tank must be inspected internally for bottom corrosion in the surrounding area (Correct answer)
- A radiograph of all adjacent shell welds must be taken
- A hydrostatic test must be performed first
Correct answer: The tank must be inspected internally for bottom corrosion in the surrounding area
API 653 requires evaluating the full extent of deterioration, so adjacent bottom plate condition must be assessed before repairing the shell-to-bottom weld.
API 653 Repair and Alteration 3
Per API 653, what is required before welding a repair patch on a tank that has contained flammable product?