Pin Hole leaks on jacketed pessure vessel
Pin Hole leaks on jacketed pessure vessel
(OP)
All,
We notice pin hole leak as shown in the attachment. This is a jacketed pressure vessel with 304 shell and 517 CS jacket with internal baffles for chilled water. Could you please shed some light on damage cause?
Chilled water is DI water at 47 F which is treated with molybdate. pH of chilled water is 8 to 9.
When grinding the vessel, we did not find general thinning of the vessel wall (1/4" thick). Upon grinding, we noticed the pin hole is located right above the baffle (Stitch welded to the shell). During grinding, the wall thickness was close 1/4" indicating there is no general thinning of the wall.
Appreciate for your help.
We notice pin hole leak as shown in the attachment. This is a jacketed pressure vessel with 304 shell and 517 CS jacket with internal baffles for chilled water. Could you please shed some light on damage cause?
Chilled water is DI water at 47 F which is treated with molybdate. pH of chilled water is 8 to 9.
When grinding the vessel, we did not find general thinning of the vessel wall (1/4" thick). Upon grinding, we noticed the pin hole is located right above the baffle (Stitch welded to the shell). During grinding, the wall thickness was close 1/4" indicating there is no general thinning of the wall.
Appreciate for your help.





RE: Pin Hole leaks on jacketed pessure vessel
Is this in service? How long?
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P.E. Metallurgy, Plymouth Tube
RE: Pin Hole leaks on jacketed pessure vessel
The crack is on jacket wall. The baffles are stitch welded to the shell wall and there is about 1/8" gap between the baffle circumference and jacket i.d .
This vessel has been in service for 25 years and has never been taken out of service except for shutdowns.
I assumed under deposit corrosion as i have seen red sludge on the surface of the baffle as well as on the shell wall. However, the baffles which are made of same material (SA517), have no signs of pitting corrosion.
Appreciate for your help.
Thanks
RE: Pin Hole leaks on jacketed pessure vessel
Do these leak?
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P.E. Metallurgy, Plymouth Tube
RE: Pin Hole leaks on jacketed pessure vessel
I agree with you that there could be tight fit in certain areas that could contribute for crevice corrosion. I did not see any corrosion signs on the baffles. See attached picture showing the baffle.
RE: Pin Hole leaks on jacketed pessure vessel
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P.E. Metallurgy, Plymouth Tube
RE: Pin Hole leaks on jacketed pessure vessel
From the pictures, I ruled out crevice corrosion. Appreciate your help.
RE: Pin Hole leaks on jacketed pessure vessel
thanks
RE: Pin Hole leaks on jacketed pessure vessel
RE: Pin Hole leaks on jacketed pessure vessel
Thanks for your response. There is no crevice between the baffle and jacket wall. The last picture of the plate is upside down.
The baffle is stitch welded to the jacket wall on the top side (3" weld). The 1/4" baffle is around the read area. Right above the baffle you see a ridge which seem to be weld and the crack is right on top of the weld location.
The crack is as long as the weld section is. We identified 8 such cracks and all are loacted right above the weld. We cut a section off as shown in the attached pictures. For the rest, we ground the cracked area and welded it back. The grinder went through the stitch welds for all 7 cracks.
RE: Pin Hole leaks on jacketed pessure vessel
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P.E. Metallurgy, Plymouth Tube
RE: Pin Hole leaks on jacketed pessure vessel
I have attached some studies done on the cracked plate along with the pictures. It seems more like a thermal fatigue at the welds. There is 90 degree temperature swing at least 3 times/day.
Appreciate your thoughts.
RE: Pin Hole leaks on jacketed pessure vessel
What is the mean operating temperature of the jacket? 90 degrees (C??) of temperature change, once every 8 hours, is a relatively low level of thermal loading.
RE: Pin Hole leaks on jacketed pessure vessel
RE: Pin Hole leaks on jacketed pessure vessel
Given the amount of sludge, and surface corrosion, visible on the baffles in your photos, the other posters pointing out corrosion issues look to be correct.
In any event, a failure after 25 years of continuous service seems to me to be a pretty reasonable track record. The hard part will be cleaning all of the corrosion out of the jacket to avoid this problem popping up in other areas that you haven't yet inspected. My suspicion would be that the conditions that caused this pinhole in this area are present in other locations as well, and if they aren't leaking yet they will be eventually.
RE: Pin Hole leaks on jacketed pessure vessel
It is hard to see the bulges with naked eye for 5 ft away. I notice when I was looking at the defects about a feet away from the wall and felt it.
Thanks
RE: Pin Hole leaks on jacketed pessure vessel
All of your photos, explanation, and data point directly at a corrosion problem. The two other posters in this thread are posters who are well known on this board as excellent technical resources, and they are all saying the same thing.
RE: Pin Hole leaks on jacketed pessure vessel
This still looks like primarily a corrosion issue to me.
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P.E. Metallurgy, Plymouth Tube
RE: Pin Hole leaks on jacketed pessure vessel
Thanks. 4 years ago, the chilled water is switched from regular industrial water (clarified water with pH 8 to 9) that was treated with nitrite type chemical to Demineralized water (pH 7.0) treated with Molybdate ( >100 ppm with water pH at 8 to 9).
Last week we inspected another vessel with same design, service and operating conditions as the failed vessel in discussion and found out that the vessel jacket has lost entire 40% of wall thickness. Shear wave indicated pitting corrosion.
I would like to know if the DI water is causing this corrosion problem even with molybdate treatment.
RE: Pin Hole leaks on jacketed pessure vessel
I trust that lab samples were run, giving them a long term exposure in the old water, and then into the new and checking to see that they remained passive?
There is also the issue of dissolved gasses in the water. This could be very different between the two waters and could be playing a role.
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P.E. Metallurgy, Plymouth Tube