Repair options for leakage in a regenerator (Heat exchanger)
Repair options for leakage in a regenerator (Heat exchanger)
(OP)
SHELL SIDE SERVICE: CATACARB SOLUTION
TUBE SIDE: EFFLUENT GAS-H2, NH3, etc
TEMPERATURE catacarb 120C
shell MATERIAL: A285 Gr C clad with ss 304
Tube side material: 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, also tubes were leaking from near the expanded joint.
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.
Chloride ppm in catacarb solution is 50 ppm at 120 degree C.
Also how to repair the two types of leakage as welding is not effective and plugging may not rectify the leakage from the rolled joint space between tube & tubesheet.
refer to the drawing.
the tubesheet is double and the weep holes have been plugged o get rid of leakages
TUBE SIDE: EFFLUENT GAS-H2, NH3, etc
TEMPERATURE catacarb 120C
shell MATERIAL: A285 Gr C clad with ss 304
Tube side material: 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, also tubes were leaking from near the expanded joint.
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.
Chloride ppm in catacarb solution is 50 ppm at 120 degree C.
Also how to repair the two types of leakage as welding is not effective and plugging may not rectify the leakage from the rolled joint space between tube & tubesheet.
refer to the drawing.
the tubesheet is double and the weep holes have been plugged o get rid of leakages





RE: Repair options for leakage in a regenerator (Heat exchanger)
Once you have leaking between and plug the weep holes it is all over.
There are lots of ways to mess up tube to tubesheet joints.
Rolling too near to the back face of the TS or too near to the weld will cause cracking. Welding without proper rolling will put all of the load on the welds and cause cracking also.
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P.E. Metallurgy, Plymouth Tube
RE: Repair options for leakage in a regenerator (Heat exchanger)
RE: Repair options for leakage in a regenerator (Heat exchanger)
We have two such heat exchangers currently in operation. We have ordered one new bundle with modified design i.e. having a single tube-sheet. But our concern is that similar problems maybe seen in the second Heat exchanger which was not inspected in our last TA’15.
As a preventive measure, what could be our way forward for the second heat exchanger? We intend to go for repair options.
“Once you have leaking between and plug the weep holes it is all over.”
Can you elaborate this point? I mean we can remove the plug from the weep hole and would like to go for an option for repair of the leakages.
RE: Repair options for leakage in a regenerator (Heat exchanger)
I think plate type heat exchanger would not be a good choice as we have effluent gas at one side. furthermore catacarb crytallization maybe a problem.
Is it easier to clean plate type HX or shell & tube HX?
RE: Repair options for leakage in a regenerator (Heat exchanger)
Another option to consider would be a spiral HE manufactured by Alfa Laval.
Else you may have to spend a lot more money for a more corrosion resistant S/T HE.
A less corrosive solvent than catacarb would be what many modern plants have : activated MDEA - doped with piperazine.
RE: Repair options for leakage in a regenerator (Heat exchanger)
My company will be reluctant to go for such a change. I will explore the possibility though.
Is changing the material of present HX the only option to get rid of SCC?
any options for the repair of leakages that we are encountering?
RE: Repair options for leakage in a regenerator (Heat exchanger)
These designs are not meant to have those vents plugged, you are crating stresses that were not anticipated.
Material change is the only way to get away from SCC. What are other people doing? Are these being built in 2205? That might be an option for both tubes and tubesheets, using thinner tubes.
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P.E. Metallurgy, Plymouth Tube
RE: Repair options for leakage in a regenerator (Heat exchanger)
RE: Repair options for leakage in a regenerator (Heat exchanger)
I have forwarded my recommendations of re-evaluating the design & material & checking the process parameters.
As it clearly indicates that SCC is the problem
RE: Repair options for leakage in a regenerator (Heat exchanger)
RE: Repair options for leakage in a regenerator (Heat exchanger)
maybe you are right & chlorides should not be present. Will send my queries to process department for clarifications.
nice direction of thinking!!!!!
RE: Repair options for leakage in a regenerator (Heat exchanger)
According to experience, the inhibited CATACARB solution has greatly reduced the chance of occurrence, even with a normal chloride level of 200-400 ppm. However, the chloride content should still be tested occasionally and monitored. To minimize chloride contamination, all makeup chemicals should have low chlorides, normally less than 100 ppm.
this is the reply that i got
RE: Repair options for leakage in a regenerator (Heat exchanger)
a)What is the operating pH range for the catacarb solution where this failure occured - the pH would have been low if this is the CO2 rich catacarb solution. From what I read, a pH of less than 10 is required for CL SCC
b)Is the licensor quoted permitted 200-400ppm chloride level relevant for non sensitized SS304 or for materials that have become sensitized, also what is the pH for which this permitted level is allowed?
RE: Repair options for leakage in a regenerator (Heat exchanger)
presently new catacarb solution data is as under:
CATACARB CATALYST 400:pH (10% AQ. SOLUTION): 11-12
CATACARB INHIBITOR 922A:pH (5% AQ. SOLUTION): 12.1
CATACARB DEFOAMER WBU:pH: 7
But i dont have the pH of catacarb after absorption of co2. working on that!!!
Is the licensor quoted permitted 200-400ppm chloride level relevant for non sensitized SS304 or for materials that have become sensitized
how sensitization is a problem here?
i dont think sensitization temperatures are achieved
RE: Repair options for leakage in a regenerator (Heat exchanger)
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P.E. Metallurgy, Plymouth Tube
RE: Repair options for leakage in a regenerator (Heat exchanger)
RE: Repair options for leakage in a regenerator (Heat exchanger)