Many operators used graded systems of levels of atmospheric corrosion in their corrosion control plans. Sometimes atmospheric corrosion is not well defined in these plans and may actually include minor surface oxidation. PHMSA in its guidance documents for corrosion has defined atmospheric corrosion as noted below which does not include minor surface oxidation:
Atmospheric Corrosion is an area of metal loss due to general corrosion, localized corrosion pitting, or peeling scale on the steel surface that has damaged the pipe. Surface oxide is corrosion and if allowed to continue may affect the safe operation of the pipeline at some point in the future. Oxidation (or “light surface oxide”) can be defined as the slow rusting of pipe which is not yet considered to be atmospheric corrosion because there is no evidence of metal loss at this time.
Note that there must be metal loss for PHMSA to consider that atmospheric corrosion has occurred thus requiring action as noted below.
192.481 Atmospheric corrosion control: Monitoring.
- c) If atmospheric corrosion is found during an inspection, the operator must provide protection against the corrosion as required by § 192.479.
192.479 Atmospheric corrosion control: General.
(a) Each operator must clean and coat each pipeline or portion of pipeline that is exposed to the atmosphere, except pipelines under paragraph (c) of this section.
(b) Coating material must be suitable for the prevention of atmospheric corrosion.
(c) Except portions of pipelines in offshore splash zones or soil-to-air interfaces, the operator need not protect from atmospheric corrosion any pipeline for which the operator demonstrates by test, investigation, or experience appropriate to the environment of the pipeline that corrosion will—
(1) Only be a light surface oxide; or
(2) Not affect the safe operation of the pipeline before the next scheduled inspection.
I recommend you review your plan to ensure your definition of atmospheric corrosion aligns with PHMSA’s definition. If you don’t have time, I would be happy to help you with this.
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