Oil contamination near a tank weld or crevice can remain below an accessible surface and reappear after cleaning. Painting over the first clean-looking state can trap the unresolved source. The repair needs both a surface check and an explanation of where the oil came from. [1]
Work through the evidence
Map the contaminated region and identify any active leak or connected crevice.
Distinguish loose surface oil from repeated emergence at the same location.
Use the coating system’s approved preparation and cleaning method.
Recheck the defined region under the relevant inspection interval and condition.
Confirm the compatible repair film and its final cure/adhesion evidence.
The sequence does not prescribe solvent, heating or leak repair. An active oil-retaining defect is a separate mechanical problem that cosmetic coating cannot solve.
Keep temperature and timing in the recheck
Oil mobility and surface appearance can change with temperature. Record the condition of the inspection and whether it represents the repair’s intended service boundary. A short cold check may leave uncertainty about contamination returning later.
Choose a cleanliness verification accepted by the coating system. A dry cloth or visual inspection can be one observation, but its scope should be stated. Do not equate the absence of visible sheen with zero residue or guaranteed adhesion.
Keep paint execution and supervision tied to the actual product and coated region; a finished appearance does not recover missing process evidence. [2]
Distinguish repeated contamination from first-clean appearance
Assume a validated same-area extraction finds 10 mg residue initially, 2 mg after cleaning and 6 mg after an agreed dwell. Reappearance is 4 mg, indicating that the first cleaned state was not stable under that condition. Investigate source and crevice transport before accepting the coating repair; these masses are not cleanliness limits.
References
- ISO, ISO 12944-4:2017, Paints and varnishes — Corrosion protection of steel structures by protective paint systems — Part 4: Types of surface and surface preparation.
- ISO, ISO 12944-7:2017, Paints and varnishes — Corrosion protection of steel structures by protective paint systems — Part 7: Execution and supervision of paint work.