Maximum corrosion for tube to tubesheet joints

[kweesh]

Hello,

I have an air cooled heat exchanger in which the Carbon Steel (SA-214)tubes are suffering from random pitting damage of up 45% wall thickness along the length of the tube. The tubesheet joint is an expanded type with a double groove. Can anyone point me to a fitness for service calculation that lets me determine what the minimum thickness for the tube in the tubesheet joint is allowed to be. My thinking is that the thinning of the tube in this area would reduce the strength of the joint leading to loosening of the tube. The exchanger is designed to ASME VIII and specifies a 2mm corrosion allowance. The tubes had an original nominal WT of 2.77mm. Its not clear if the corrosion allowance takes the expanded tube area into account.

I'm not sure if there is a minimum allowable thickness for these type of joints so please let me know if i going along the wrong path. I have a calculated a minimum thickness for pressure retention and structural strength using ASME VIII but I thought this would be another check I should do.

Kweesh

 

[SnTMan]

kweesh, I am not familiar with air cooler design, so kind of throwing this out.

Is the tube-ts joint subject to longitudinal loading, and / or is the joint allowable load calculated per Apx A? If a longitudinal load is known, perhaps the equivalent joint strength can calculated from Apx A, based on the reduced wall thickness.

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[kweesh]

Hi Mike,

Thanks for the response. I think the calculation in Appendix A is suitable for what I need. Thank you for your help.

Regards,

Kweesh

 

[r6155]

No corrosion allowance shall be provided for tubes.
See API 661

Regards
r6155