We are seeing small bulges in the internal liner of a multi-wall reactor vessel. It appears that in the bottom third of the reactor, the liner has pulled away from the wall in several places. We think that this may have been caused by some form of pressure surge. Has any one experienced a similar phenomena?
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Liner bulge in pressure vessel
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Can you comeback with a better physical description of the vessel and liner, like liner material thickness , how was it attached, how was it checked prior to being put into service and anything else that might help.
Vessel material and operating conditions.
Process media and conditions.
Design conditions of the vessel.
Vessel material and operating conditions.
Process media and conditions.
Design conditions of the vessel.
Longinthetooth
Chemical
If you have a lot of hydrogen present you could have hydrogen blisters. This is a qwell known phemomona.
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Go to the message box and look at Step 3. You can link directly to files location or better upload it to by clicking on the link provided.
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48" ID vessel designed for 3800psig pressure at 420F with a flat top....??? (how thick?? - must be huge..!!)
Is the 1/2" thick internal liner integraly clad? or weld overlaid?
If it is I have never seen such a thickness of liner like this before - typically 3mm thick.
If it isn't - how is the liner attached...??
Is the 1/2" thick internal liner integraly clad? or weld overlaid?
If it is I have never seen such a thickness of liner like this before - typically 3mm thick.
If it isn't - how is the liner attached...??
Have you checked the weld directly above the bulge as it looks like the the worm got off line.
I would clean weld and area very good and take something like a 3M wheel and buff the area to remove any skin coating and then PT this area. On the PT testing, after the weld is cleaned and still a little warmer than the surrounding area I would spray a light coat of developer and see if it you pick up any wet spots. If nothing shows clean the area with PT cleaner and perform the a normal PT with a long soak time with the dye. When cleaned watch the developer as it dries as you might see a line of very small spots. If you you see this touch the area with a grinding wheel and reapply the developer to see if there is a crack.
If you don't see any spots let the developer stay for the same time as the dye.
I would clean weld and area very good and take something like a 3M wheel and buff the area to remove any skin coating and then PT this area. On the PT testing, after the weld is cleaned and still a little warmer than the surrounding area I would spray a light coat of developer and see if it you pick up any wet spots. If nothing shows clean the area with PT cleaner and perform the a normal PT with a long soak time with the dye. When cleaned watch the developer as it dries as you might see a line of very small spots. If you you see this touch the area with a grinding wheel and reapply the developer to see if there is a crack.
If you don't see any spots let the developer stay for the same time as the dye.
Bulges can be formed by localised hot spots. If there's an insulating lining then any wear in the lining can cause a hot spot. The radial expansion of the hot spot will produce a bulge in the shell and the lower yield stress can cause permanent deformation. Generally if the bulge is less than 1% of the diameter then it satisfies vessel codes circumferentially, but you may need to assess the bulged shape properly using FE.
corus
corus
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We did further NDT and have proved that these are not liner bulges but uneven wear on the liner. Earlier UT readings had erroneously indicated uniform thickness of liner leading us to believe that the liner had distorted. Carefully re-doing the UT checks has confirmed that actually the liner has not moved but has corroded unevenly. We are still at a loss for the reason for this uneven wear.
As corrosion has been identified as the cause of the apparent bulges, liner thinning will likely continue given the corrosivity of the process, I have seen zirconium used in place of 316L, however very expensive.
Interestingly, I've seen damage in a similar reactor - so I draw your attention towards possible pinholing of the liner:
Carbamate may get behind your liner and corrode the carbon steel shell, one possibility is the corrosion product is swelling causing the bulging. I have seen *severe* corrosion of the CS shell in a similar reactor from this reason.
Carbamate corrosion in this type of vessel design is particularly insidious, it can be very rapid and go undetected. Can you UT your pressure shell from the OD to check the CS thickness/integrity?
The other problem is the carbamate/urea melt gets behind the liner and tracks to the weep holes, however it can solidify and block said holes with a cementous like product. When the pressure is decreased inside the vessel via process, the volume of gas trapped between CS shell and liner may expand and cause bulging/buckling in your liner.
Just a thought...
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Good comments. We have checked out the weephole system and verified that these are clear.
Some of the baffle trays had tilted and possibly this set up uneven internal flows causing the uneven wear.
We repair pinholes on the liner every time we open the reactor (2 year frequency).
Some of the baffle trays had tilted and possibly this set up uneven internal flows causing the uneven wear.
We repair pinholes on the liner every time we open the reactor (2 year frequency).
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