Pressure vessel thickness U.S. measurement

[guideonl]

Hi everyone,
In purpose to estimate the corrosion degredation in pressure vessels it is recommended to measure the pressure vessel thickness using an U.S. device.

My question is how to determine the number of test points on the shell/caps surface as a function of the pressure vessel size? (50-5000 liters). Actually, I'm using 3-4 test points on the shell surface & 2 test points on each cap surface of a 250 liter tank, but I don't know if it is many/few... are there any recommendations?

Second question is how to determine the thickness, using the minimum/mean test point thickness? Actually I use the min T.P.
Thank you
Guideon

 

[Tom.G]

Rather out of my field, but here are a couple places to start
https://www.flyability.com/corrosion-monitoring

above found with:
https://www.google.com/search?&q=measure+corrosion+degredation+in+pressure+vessels

https://www.google.com/search?&q=inspection+corrosion+in+pressure+vessels

Doing a quick read of the first reference, inspection seems to consist of:
1) visual to locate corrosion and its extent
2) ultrasonic or X-ray measurement of minimum remaining wall thickness
3) engineering evaluation of remaining wall thickness versus operating conditions

For large vessels, a drone airplane with a camera is flown around inside the vessel to locate and measure the extent of any corrosion.

Note the reference to minimum thickness, that is where failure is likely.

Pay particular attention at welds and surrounding Heat Affected Zones (HAZ).
Inspection frequency depends on pressure, material being contained, pressure cycles, etc. Inspection periods vary from "as often as possible", 1-2 years, 4-5 years.

One project I know of for a steam boiler used "Test Coupons" monitoring. I had the impression these were small pieces of material (metal) that were located in the boiler or adjacent plumbing and were periodically sent to a lab for testing, and replaced with new ones; testing occurred 1 or 4 times a year.

Lets see if by mentioning his name, we can get @jrmichler to respond here, he has a much better background in this.

Cheers,
Tom

 

[jrmichler]

I hesitated to respond in the hope that somebody else could make a better response. The above post by @Tom.G is better than I would have done.

The best places to test vary between pressure vessels. Compressed air tanks are subject to corrosion on the inside near the bottom if condensed water is not continuously and completely removed. I have seen deep pitting in a propane tank on the outside bottom where dew drained down the outside and dripped off.

You need to use your knowledge of the pressure vessel, its contents, and the environment to test the areas most subject to corrosion. That might be 1or 2 tests per vessel, or it might be 100 or 200 tests.

 

[guideonl]

Thank you for the information.