Safety Alert

​Application of radiography to measure the remaining wall thickness of external corrosion

Summary of issue

Tangential (profile) radiography is commonly used for in-service inspection of externally corroded components in the oil and gas industry. Recently it has become apparent that for some forms of localised corrosion, significant underestimates of severity can be obtained. In extreme cases, almost through-wall corrosion can be missed completely, unless the radiation source and film/detector are aligned optimally so that the tangent position is at the point of greatest wall loss. Even then, the measurements of minimum remaining wall thickness may be significantly higher than the actual value. The magnitude of this under-sizing however depends on the morphology of the corrosion, and more extended areas of corrosion can be less affected and hence may be more accurately sized.

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