Weld spatter inside an oil tank can remain attached, sit loosely on a ledge or be hidden behind a bracket. Handling and later fabrication can move it. Internal cleanliness needs to follow those paths, not only the accessible floor of the tank. [1]
Map weld zones and nearby shelves, stiffeners, corners and nozzle pockets. Identify whether the final assembly blocks the view or cleaning path. An early inspection is valuable only within the state it actually examined.
| Particle state/location | Question | Evidence |
|---|---|---|
| Attached near seam | Could it detach or interfere with insulation? | Specified surface acceptance and local inspection |
| Loose on open floor | Has it been removed? | Final cleanliness observation |
| Hidden shelf or bracket | Can the region be inspected and cleaned? | Access plan before closure |
| After later fabrication | Was new debris introduced? | Final-state check tied to operation history |
Do not substitute a magnet sweep for complete coverage
One collection method may gather some loose metal while missing attached debris, sheltered regions or other contamination. Its scope should be recorded. Choose the final cleanliness evidence required by the manufacturing plan.
Cleaning near a finished internal coating can damage that coating or leave additional residue. The restored state needs both cleanliness and surface-protection evidence where applicable.
FIST 3-31 identifies loose metal particles in transformer oil as a threat to insulation. A final internal cleanliness record therefore needs location coverage and surface condition, rather than a favorable weld-indication report alone. [2]
Close the inaccessible cleanliness area
Assume the final internal surface map covers 12 m², of which 2 m² behind attachments becomes inaccessible after closure. An inspection of only the other 10 m² covers 83.3% of that mapped boundary. Obtain the preclosure and subsequent-operation evidence for the hidden region; no surface-area percentage alone establishes particle cleanliness.
References
- U.S. Federal Highway Administration, Bridge Welding Reference Manual, FHWA-HIF-19-088, 2019.
- U.S. Bureau of Reclamation, FIST Volume 3-31, Transformer Diagnostics, June 2003.