Hi The operating condition is: Shell operating condition; P= 75 kg/cm2 , T=90 C Tube operating condition: P= 22 kg/cm2, T= 310 c. And it is same for all three heat exchangers. The unit Mothballed until 97 .In 98 it was returned to the service and in 2002 again the stainless channel box cracked and repaired at that time. In 2005 it cracked again. The flow in all heat exchangers is kerosene with sulfur as vapor from the reactor. There is a small amount of hcl gas enter to the shell but its amount very low say 1 ppm or %BD ppm. The welding Procedure will post later. Thanks Mark

Hi welding repair as the following: 1.For repair of cracks in the channel head and head-to-partition plate for exchangers num. 1& 2 , which are ASTM A204B (0.50 Mo), the use of WPS P3-3 is acceptable. PWHT will also be required. 2.Regarding the third heat exchanger , which is clad with 321 stainless steel, the use of WPS P8-2B is recommended using E308L filler metal since 321 is not available for the SMAW process. PWHT will not be necessary since welding is only to be done between the cladding and the partition plate (304L stainless steel). 3.For all repairs it is suggested to use a lower preheat (approx. 200 C) to avoid hot cracking problems. This is especially true for the third heat exchanger since the weld is between the 321 cladding and 304L partition and high interpass temperature can lead to hot cracking. 4.PMI should also be performed on third heat exchanger welds to assure that the weld metal is sufficiently similar to 321 SS. Root cause: I will not predict it is HIC problem since the h2s is vapor and the temperature is too high. IGSCC OR TGSCC is predictable since we have metal expansion through the partition cause stress on the claded 321ss . For the first and second there was wrong PWHT procedure since there was stress at the nozzle and partition plate. This is my input and any addition will be valued. Also, the shape of the crack is like knife attack at HAZ and it was in parallel. Thanks

For your third heat exchanger I am not so sure if welding with E308L was the good option. Other option is to use E347-15 or E309Cb-15 whose are stabilized electrodes like your 321 clad. Regards Luis Marques Portugal