Pipe with heater jacket over it.

[miked7]

Hello All, Here is a question for you. We have a 16" std shd pipe, flanged each end and welded to the flanges is bent plate in two semi circles to make a jacket. The inner pipe has sulphur flowing through it, the outer jacket has steam to heat the sulphur. The inner pipe is 10% Rad, and 10% Rad is called up on the jacket as well. In fact the jacket is given all the same requirements as the internal pipe. 10% rad, hydrotest etc. Reality is that it can only be MPI inspected as Rad is impractical, and hydrotest is not really practical due to configuration and air test is too dangerous. My question is, what should we be calling this jacket? as it obviously is not piping, how should we be testing it?

 

[Zapster]

Reality is that it can only be MPI inspected as Rad is impractical, and hydrotest is not really practical due to configuration and air test is too dangerous. Life is not always convenient and neither is engineering. What is the design pressure of the jacket; is there any way that the pipe/jacket could be pressurized. If your answers make it sound like a pipe or pressure vessel, then you should build and test according to the appropriate code. Under some circumstances a steam jacket might be considered an ASME BPV VIII pressure vessel.

 

[C2it]

I agree that rad is not possible but, hydrotest is usually practical for jacket pipe. But, beware of hydrotesting the jacket without consideration of possible collapse of the core pipe due to external pressure. Refer to ASME VIII UG28/29 for external pressure, otherwise ASME B31.3 should answer you needs.

 

[unclesyd]

We have steam jacketed pipe up to 8" core 10" jacket that we routinely hydrotest. Our highest steam pressure is 175 psig. The core pipe should be able to take any pressure the jacket will see so I can't see collapsing the core a problem.

 

[C2it]

Unclesyd,

The reason I mentioned core pipe collapse is that I have seen it happen, in very expensive stainless steel. An entire pipe system in nitric acid production was destroyed, by hydrotesting the jacket without consideration of the thin core pipe's ability to resist the external pressure.

 

[miked7]

Thank you Zapster, C2it and unclesyd. The issue with hydrotest is not the pressure, it is the complexity of the jacket and the fact that there is only a one inch inlet and outlet on each section. So if hydrotested there would be a problem with getting water out and drying. In conclusion, it is probably best to do MPI on welds and then a low pressure air test using something like Snoop to soap over welds and see if there is any leakage.

Do you have any idea what a pipe jacket would be constructed as, using ANSI B31.3 and calling it piping does not seem right?

Regards Miked7

 

[unclesyd]

Some of our jacketed process equipment (SS & CS) are quite complex fabrications made from pipe. These fabrications are classified as pipe, 16" core, and tested as such. We do 100% RT where possible and PT or MT else where during fabrication. As we have Therminol vapor as the heating media we usually test with He at the required test pressure. During the introduction of these components we made several modification and the consensus was we needed to hydrotest the jackets. We used demin water with an organic inhibitor to test. The equipment was then run through our cleaning process to completely dry the jacket and destroy the inhibitor.
All our other jacket pipe in this system is CS and we only He test the jacket. We have on occasion used hot Therminol at system pressure to add the thermal effect.
All our components have a 1" connections.

As your jackets are designed to use steam I can't see why using a compatible water source wouldn't be feasible if you set it up to drain. If you are worried about contamination from the test water you could use steam condensate or use low pressure steam to help dry and flush the system after the actual test.

C2it,
We have had several process where jacketed pipe was required and I've never seen any pipe where the core wasn't designed to to take the test pressure of the jacket. This was the reason for my comment. We have a large HNO3 plant on site and use HNO3 in our process to oxidize organics and I too am very leery in pressure testing any component in this service without a very through inspection first.