Hydrotest Pressure for an In-service Fin Fan Cooler

[cespi82]

Hi Gents,

I have to hydrotest the tubes of a Fin Fan Cooler and what came first to my mind was the API-510 criterion of 1.3 x MAWP x the Correction for Temperature (S Test Tem / S Des Temp).

The equipment has 5 years in service and 8 of its tubes have leaked. We have plugged the tubes out and now what is next is the hydrotest of the whole thing. Does the MAWP has to be recalculated per code as the equipment has several years in service and thickness values are not obviously the same as the initial stage?

No wall thickness data is available at this moment. If effectively the MAWP requires per code to be recalculated, should we make the effort to conduct and IRIS or similar technique in order to have thickness data and recalculate the MAWP?

How big it would be the mistake (if it is mistake) if we just hydrotest the equipment at the MAWP written on the plate?

Kind regards,

Cesar

 

[metengr]

First off, what is the failure mechanism for the leaks? Is it general corrosion, pitting corrosion? Once you figured the failure mechanism, you can decide on NDT and in-service pressure testing to find leaks, if NDT is not practicable. If you need to resort to an in-service pressure test, MAWP is just fine for this type of application.

 

[cespi82]

Thank you very much metengr,

We took out one of the failed tubes as it was on the top row. After cut it longitudinaly into halves an appreciated that the leaking point is a pitting. However, practically the tube is pitted all the way long so most probable we will have more leaks in the near future. We have placed a purchase order to get a new SS316 tube bundle.

We HTd the FFC at 1.3xMAWP as the name plate and it passed it. The fluid is productions fluids from a stimulated-steam flooded well, where siginifant quantities of water, CO2, H2S are present. Do you have any suggestion for upgrading the metallurgy?

Kind regards,

 

[metengr]

cespi82;
To be honest, I would need more information before I would provide you with a material recommendation. Information like, original tube material, length of service, specific information on process fluid (tube ID/OD), service temperature, lab analysis results of the pits, etc. Once this information has been reviewed, one can decide on material options based on cost and expected service life.