Q & A > Question Details
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)
28/10/2019 A: S Sivasankaran SABANAYAGAM, CPCL, cpclsiva@yahoo.com
Leaky tubes cN be identified only during shell test as you are doing right now.
Regarding cracks in the tube sheet, it is not clear whether the crack is on tube to tube sheet on pass partition or on the tube sheet itself. If tube sheet cracking was noticed during hydrotesting (If water was coming from the crack, then it is a through and through crack), in such case your attempt to repair the crack may not be successful.
If the tube sheet metallurgy is CS + weld overlaid with SS 321 (Normally designed in this manner for higher thickness tube sheet), then you can attempt to repair the crack by grinding, welding and in-situ machining.
Please do DPT with more dwell time on tube to tube sheet weld joints to find out any other abnormalities before proceeding with HT.