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October 27 - October 31, 2014

How does rapid depressurization affect lining performance in vessels and line pipe, and how can you identify any failure that might result?

Selected Answers

From Lydia Frenzel of Advisory Council on November 25, 2014:
As Coastal Science Associates in New Orleans, Charles and Lydia Frenzel had a designed basis accident testing (DBA) curve to follow while looking at coatings submitted for steel and concrete substrates used for nuclear plant containment vessels. We found it easy to blow off coatings if the pressure drop was sudden. The test called for quenching with boric acid solution. When three mile island occurred, our counterpart at ORNL had died and we called the "trailer" to advise them to lower the pressure very slowly as the press was saying that they were going to lower the pressure rapidly. That was years ago, I no longer have the pressure reduction curves in my files. Jack Smart has it right.

From Jack Smart of John Smart Consulting Engineers on November 3, 2014:
When internally coated tubing and vessels are used in oil and gas production containing carbon dioxide, rapid depressurization can "blow off" the coating as the carbon dioxide dissolved in the coating tries to outgas. Depressurization should be limited to a rate of about about 50 - 100 psi per minute to avoid the problem. The oil company I worked for formerly had a laboratory test procedure to evaluate the coatings and pressure reduction rate. It might not be possible to de-pressure a pipeline rapidly enough to see this occur, but it was a problem in downhole tubulars and surface production equipment.

From Warren Brand of Chicago Corrosion Group on November 2, 2014:
About 20 years ago, we did some work at Underwriters Labs, lining two water tanks which operated at around 300 psi. We were asked, at that time, to determine our "best guess" as to what would happen to the coating in the case of rapid depressurization. The coating we applied at the time was a 100% solids epoxy at roughly 40 mils. The tank was made up of a roughly 80% water and 20% of an air space, which maintained the pressure within the tank. As I recall, we assumed that the nothing would happen to the coating below the water line. This assumption was based on the coating having absorbed some water, but since liquids cannot compress at 300 psi, nothing would happen to the coating as the water absorbed into the coating would not "know" if it was under pressure or not. In the air-area, however, we postulated that there might be some damage to the coating as the air that was likely absorbed into the coating would rapidly expand, causing the coating to pop and disbond (mostly through multiple cohesive failures throughout the coating system). We believed, and I believe now, that the coating would look damaged, deformed and  like thousands of small blisters had popped. Looking forward to other thoughts.

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Tagged categories: Asia Pacific; Coating failure; EMEA (Europe, Middle East and Africa); Latin America; North America; Quality Control

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