Hi Adrian,
If the exchanger is out of service for greater part of the year, cooling water on the shell side would act as a trap, in the tight crevices of Tube to tube sheet. If so pitting and resultant pinhole leaks are very much possible in T-TS welds . It would be more appropriate to get the more operating details, chemistry of cooling water, chloride content or other halogen contents. 347 and other 300 series alloys could pit in stagnated cooing water with even > 100 ppm of chlorides. 37 years of service history is quite for an exchanger.
If the clients insist of re-hab of his exchanger based on the sound integrity of rest of the exchanger components, the repair of tube to tube sheet welds is a feasible idea. Best option would be to scoop out the old weld re-weld by manual GTAW or automatic GTAW process.
If you could provide more design/operating details, then it may an interesting case for failure analysis.
Thanks.
Pradip Goswami, P.Eng,IWE
Independent Welding & Metallurgical Engineering Specialist & Consultant.
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Adriaan Stoltz
Sent: Friday, January 22, 2016 9:07 AM
To: materials-welding@googlegroups.com
Subject: [MW:24158] s/s 347 heat exchanger
Good day experts
Upon pressure testing of a 347 s/s heat exchanger (tubes and tube sheet) we found numerous miniscule leaks through the tube-to-tubesheet welds as well as from the inner bore of the tube in the HAZ. The HE is 37 years old, not much operational history except that it is currently operating at app. 200 deg C at a pressure of 500kPa ( cooling water shellside) and 1200kPa (heat transfer oil tube side)
Tubesheet 40mm thick.
Tubes 3/8’’ od 1.2mm thick
My questions:
1. What could be the cause of weld and tube failures?
2. Preferred procedure for repair?
Your input is greatly appreciated.
Regards.
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