Remaining Service Life of Gas Sphere Calculation 2

[PeterHerman]

We are calculating the remainign service life of a welded steel gas sphere and it seems the methodology is to develop the (1) corrosion rate and then (2) calculate the remaining life using the rate. The corrosion rate is determined by the change in initial thickness minus the actual thickness over time. What I find very conservative is that the initial thickness is, in practice, increased by the maximum permissible variation in fabrication (for me ASTM A20M-06) and this adds about 10 percent. Naturally, this results in a conservative corrosion rate. Is there a more sophisticated way to approach this?

 

[metengr]

That is correct, and most user's would rather error on the conservative side versus failure of a pressure vessel. Unless you have actual thickness numbers for the pressure vessel plate to validate a lesser conservative corrosion rate, I would suggest you stick with the conservative corrosion rate.

 

[Duwe6]

And remeasure every year or two. The ACTUAL thicknesses will soon flatten out your corrosion curve. It is possible that you actually have no corosion losses. Until the data set has 'actuals' from at least 5 years, corrosion rate is really a guess.

 

[SJones]

http://www.hse.gov.uk/research/rrpdf/rr016.pdf

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04