This is with reference to High pressure exchanger overhauling job being carried out at DHT unit during ongoing Turnaround Shutdown. During Shell side combined hydro testing of Effluent-Feed Hot Exchangers bank (90E03A,B,C,D) to attend suspected leaks, cracks found in one of the exchanger (90E03D) tube sheet near Pass partition plate weld joint. Please refer attached photographs for location of cracks observed and also attached exchanger drawings. Thickness of Tube sheet is 372 mm and metallurgy is SS 321. Presently, grinding of T/s Crack location was done up to 15 mm and still crack exists.
Prior to finding cracks, profuse leaks from some tubes (67 nos in 90E03C, 6 no in 90E03D where T/S cracks found) were observed during hydro testing @ 127 Kg/cm2 (HT Pressures: Shell-127 Kg/cm2. Tube-227 Kg/cm2). These leaky tubes were plugged with SS 321 plugs using TIG filler wise ER347 and subsequently hydro test was done during which one crack in T/S observed.
In this regard, we require urgent guidance to understand repair methodology/testing etc.
(Photos & video i want to share but unable to do)