Vessel Jacket Best Practices

[russtcan]

Hello,

I'm putting together a Best Practice for Vessel Jackets. It will include the fabrication process and applications for conventional, half-pipe, and dimple jackets. I was wondering if anyone had any ideas of some common problems and what to look for when fabricating the vessel jacket that's not necessarily written in the ASME code but is based on experience and lessons learned. Additionally, I would like to get an idea of some applications of each jacket and which one is best suited for certain applications.

Thanks

 

[DSB123]

Hi,
One big problem for jacketted vessels is the differential pressure during hydrotesting of the jacket. If you are not careful of the application of the test pressure then you can exceed the allowable pressure for the inner vessel. Normal "trick" is to pressurise the inner vessel to ensure the differential external pressure does not exceed the allowable.

 

[Duwe6]

During fabrication, take a set of UT thickness readings of the jacketed portion of the inner shell to give future Inspx 'actual' vs. 'nominal' thicknesses. Put the readings & a sketch of their locations into the vessel records. Reason is that the thickness of the primary, inner, shell will become inaccessible without enptying, cleaning, decontamination, and a Confined Space entry. You want to keep these Internal Inspx's w/Entry at the 10-year normal rate as long as possible.

If the vessel was constructed as * 0.500" nominal * amd there is a spot that actually reads 0.494", that first Internal Inspx at X years will give a Corrosion Rate of 6 mils per X years. The proper action when you see that high a Corrosion Rate is to go back into the vessel in x/2 years and see if the calculated Corrosion Rate is 'real', or came from a pre-existing 'thin' spot. Taking and mapping some thicknesses during construction, or at delivery [prior to comissioning] will save 1 to 3 unneeded Confined Space entries, at many thousands of $$$.

 

[MJCronin]

If you include half-pipe heating jackets in your guideline, you should discuss the welding options offered between the half-pipe and the vessel shell.

Some years ago, I was involved in a half-pipe reactor design for a major Pittsburgh chemical company. The two otions offered by the fabricator were fillet welded and full penetration welded. I was told that the full penetration welded design would sustain cycling thermal service much, much better than the cheaper fillet welded design.

The full penetration option would take much longer and was subject to additional QC.

Since the chemical reactor vessel would be subject to many deep thermal cycles in service, the client selected the full penetration design.

 

[russtcan]

Thanks for all the info guys. I pretty much got most of what I need; however i'm a little short on dimple jackets. Does anyone know of some best practices for specifically dimple jackets? THANKS