DESCRIPTION SHELL SIDE TUBE SIDE
SERVICE CATACARB SOLUTION EFFLUENT GAS-H2, NH3, etc
TEMPERATURE 120°C
MATERIAL A285 Gr C clad with ss 304 ASTM A213 TP 304L

We have a semi-lean generator which regenerates catacarb soluton in ammonia plant, the specs of which are given above.
During TA 2015, failure of weld joint of tube-tubesheet weld was observed.
When repair welding is done. More cracks are generated in the tubesheet which propagate to other weld joints of nearby tubes.
Tubesheet material is A240 TP304.
Any idea what might be the reason.
If scc is the cause then it should also effect the tubes but on the contrary, tubesheet is generating cracks and the weld seam is failing.
Chloride ppm in catacarb solution is 50 ppm at 120 degree C.