Overview of Damage Mechanism

I have one experience on a Syngas line where we noticed a crack from the weldtoe towards the flange.

It was later identified as Chloride Stress Corrosion Cracking.

Its a type of Damage Mechanism.

What is Damage mechanism?

Well damage mechanism is a term very typically used in the Oil and Gas industry to describe mechanical or chemical processes which result in equipment (or piping) damage or material degradation.

The damage could be corrosion, cracking, heat damage and well, so much more.

Susceptability of a particular material or equipment is dependant upon several variables such as material of construction, process fluids, operating conditions, external environment and many-many others.

Like my particular case, chloride is kryptonight to stainless steel. Add stresses in the mixed, you will get CLSCC (Chloride Stress Corrosion Cracking)

That is the reason why we limit chloride content to less than 50ppm for stainless steel hydrotest.

Overtime, we as Engineers must have a good grasp of the variatey of Damage Mechanism. It is essential for creating an effective inspection strategy.

Once we have understood the damage mechanism and morphology, inspection engineers can use the info to select the correct inspection methods with the highest probability of detecting, characterizing and measuring potential damage.

Inspection intervals can be established using these industry codes and standards such as API 510, 570, 653, API RP 579 for fitness-for-service, and API 580 and 581 for risk-based inspection.

Till next time!

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