High Temperature Piping Flanges Insulation

[sahsanb]

Dear All,

With most of the high temperature pipe line generally insulated, valve bodies and flange joints are typically not insulated. I have gone through piping specifications governing our piping and they have not recommended insulating the flange joints or valve bodies unless they are steam traced. As per my understanding one of the main reasons for not recommending insulation on the said locations is to allow early detection of leakages. Request your expert opinion on highlighting any other reason for not recommending high temperature piping flanges to be insulated besides the fact that insulation may mask small leakages. Thanks.

Regards,

 

[moltenmetal]

We insulate flanged joints with removable flange insulation covers. Leaving them bare isn't a practical solution.

 

[mk3223]

In the existing facilities, one may see the valves and flanges in the high temperature service without insulation, as mentioned above. But, due to the energy efficiency and many safety incidents of burning, it recommends to cover the valves and flanges with the removable insulation blankets.

 

[sahsanb]

Thank you gentlemen for your valuable feedback. While I do understand there are demerits like heat losses in uninsulated flanges, need some confirmation on weather the only con for insulating the flanges is not being able to detect small leakages. Thanks

 

[sahsanb]

Managed to review some literature on this issue and besides delayed detection of minor leakages, flange bolts clamp load can also get effected due to insulation installation. Clamp load is the tension created in a fastener when it is tightened. Flanges and fastener are typically made of slightly dissimilar materials and hence have different coefficient of thermal expansions. While differential expansion can cause loss of clamp load it can be further aggravated if there is significant difference in individual bolts temperatures. Bolt temperatures can vary as much as 220oF between the bolt at 6 ‘ o clock position as compared to a bolt at 12’ o clock position. Bolt at 6’ o clock position will be at lower temperatures due to cooler air adjacent to it as compared to a bolt at 12 ‘ o clock position.

Request your views on this.

 

[mk3223]

Is the flange uninsulated so the air temperature is different at 6 O'clock and 12 O'clock? If it's true, the insulated flange won't have this issue.

 

[saplanti]

If you do not insulate flanges and valve you need to expect some temperature differences between fluid contacted surface and air/rain cooling surfaces. This will additionally create high thermal stresses on the flanges/valves. When we design the equipment we do not normally consider this as operational loads as far as I know. Some cases the equipment may not be able to handle these additional stresses, sometimes it will fail sometime later. Especially, the rain will be cooling external surfaces very fast. The differential thermal stress will get higher in every rain, and the life of the equipment will be a lot shorter.

You made the points on the bolting side of the flanges, that is true. However this can be eliminated by selection the adequate materials which are recommended by the codes. In case the system is very important and does not accept any leak then you need to change either the flange/sealing types or use special bolting design for the purpose or both.

Making the equipment insulated all sides provide adequate stress distribution on the system. However you still need to be careful with cold start-up heating and shut down cooling of the system anyway.

 

[EdStainless]

In some processes, such as where even small leaks are fatal, they will put shields over the flanges that have an airgap. This way you can prevent burns, and keep rain (or other chemicals) off of the flanges, but they are still open and visible.

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P.E. Metallurgy, Plymouth Tube

 

[blacksmith37]

Fasteners like B-7 will "relax" the clamping load at moderate temps like 500F and lower. And will creep at higher temps like 800F .

 

[DSB123]

Exposed flanged and valve can be a personnel "burn" risk. If the surface temperature is above 60 Deg C you should at least apply PP insulation to protect personnel where they could inadvertantly touch the bare surface.