Flange Mounted Pipe Supports 1

[GSDGoBucks]

As part of a project in the refining industry, this project recently received from the supplier a seal gas & conditioning auxiliary unit to a centrifugal compressor. Design conditions are 1175 psig @ 200F. Our engineering practices of such auxiliary units to rotating equipment require all supports and parts to conform with B31.3 and MSS-58 and MSS-69.

Was asked by a project inspector to determine if multiple flange mounted pipe supports are allowed per code. Basically these are base supports utilizing pipe welded to the floor of the unit and plate bolted to the flange assembly. The plate has two holes drilled to meet the bolt circle to a part of the flange. The plate is attached outside of the joint between the flange and the nuts. The inspector believes this is a nonformance issue.

After some research, since it would appear such flange mounted pipe supports do not fall under MSS-58, my interpretation of B31.3 is that these type of supports would fall under as an “Unlisted Material” and Para 323.1.2 from B31.3 would apply.

Is there anything I am missing from a code perspective that should also be considered or that disallows such supports. Also does anyone have reliability concerns or have experiences with failures with these type of supports.

Thanks in advance for your feedback.

 

[MJCronin]

I have been involved with these types of supports....... but only for low-pressure FRP piping systems

The reason that this design was attractive for these systems was that:

- The pipe support was place where the load existed, at a flanged valve.
- There was no vibration
- Support on the FRP piping would involve protective FRP pads, attached to the pipe wall to prevent fretting and distribute the load.

We also had a plate large enough for four flanged bolts.....not two

I do not understand why more conventional pipe supports cannot be used in your situation. What is the advantage here ?

I see these flange mounted supports as a potential failure point, especially in the event of piping vibration/ and a possible fire hazard.

Was there an engineering calculation performed to evaluate the effects of the additional shear stress on the bolts ?

 

[GSDGoBucks]

I have similar concerns related to potential future failure points. In addition to shear stress on the studs, I asked if there were any concerns to potential damage to the plate material while torqueing the studs specifically the area of the plate under direct compression where the plate could "flow" plastically leading to thinning of the plate and lowering of the clamping force supplied by the studs involved. The plate is not hardened like a washer spec. The supplier's response was less than adequate IMO so I focused my attention as noted above on MSS-58 and "Unlisted Components" as defined by the code.

Flanges involved are 2" and under, 900 class flanges.

Thanks for your input.

 

[LittleInch]

It would bbe great if you could add a sketch of the system as I still can't get my head around what the pipe has to do with it - "utilizing pipe welded to the floor of the unit and plate bolted to the flange assembly.

However whilst I have seen these sorts of supports, they are more commonly the other way round, i.e. the pipe supporting another bit of kit such as an instrument or sometimes even addiitonal support for an actuator.

My issue with them is that if you need to dismantle the pipework, your support dissapaears or makes taking the bolts out difficult unless you lift the flanges up. I can't see why the supplier can't utilse cup type supports under the flanges themselves.

For #900 pipe I certainly would have my concerns about it. If forced to use them then use over sized stud bolts and bolt it betweeen one nut which secures the flange and a second nut securing the support.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way