Hi maybe this topyc is not correct to this web site, but you could help us. We are very appreciated if you can help us with the follow suggestion.



He have a Main Steam Line that work at 970 ºF, The flexibility analysis establish the transversal load near 3000 lb and vertical load near 4000 lb, what is the material more conservative to use in sliding support?. We considered that use A36 is not appropriated to effort at 970 ºF, could be used A287 but it give a short range of work, and use A387 that is bigger range but it’s very expensive.

Hi Ivan,

My first choice would be to use a rod hanger or a trapeze with two rods. After that you would not have a lot of options. If the hanger option is not possible and I had to use a sliding support I would use the plate analog to the type of pipe. Presumably at 970 degrees F you would use ASTM A-335 P22 pipe and you would have to go with the ASTM A-387 grade 22 for the support weldment. Sorry I cannot find a silver bullet for this one.

Regards, John

Ivan,

I would not use use integrally welded support for this temperature that will cause large temperature gradient on the support during the operation and this may cause large internal thermal stresses at the connection to the pipe. If you can use the rod hangers as John Breen suggested you have the best solution.

In case you need to support the pipe underside I suggest you to use a clamped saddle with rotational restraints integral to the pipe.

Kind regards,

Ibrahim Demir

Mr John and Ibrahim,

We have to support the pipe underside, is not possible use rod hanger. Clamped saddle with rotational restraints could be used, ASTM A387 P22 is the best material to this condition, but its very expensive. Too we found that ASTM 287 have stress allowble 4000 psi at 1000 degree F, and is posible to use it growing the number of clamps and cross section, but in found too, in the manufacture catalogues its material is not used to support, maybe ASTM 287 do not have a good duration (in the time) at this temperature, we are appreciated if someone have any comments.

Ivan Abril

Mr John and Ibrahim,

We have to support the pipe underside, is not possible use rod hanger. Clamped saddle with rotational restraints could be used, ASTM A387 P22 is the best material to this condition, but its very expensive. Too we found that ASTM 287 have stress allowble 4000 psi at 1000 degree F, and is posible to use it growing the number of clamps and cross section, but in found too, in the manufacture catalogues its material is not used to support, maybe ASTM 287 do not have a good duration (in the time) at this temperature, we are appreciated if someone have any comments.

Ivan Abril

Ivan,

I would contact one of the clamp support supplier to get the support. The selected material A287 Gr 22 is adequate, however I would leave it to the support manufacturer for the allocated design temperature.

The respected support manufacturers do tests for the temperature distribution on the supports and use adequate material. The clamp may be at the same temperature of the pipe, however the saddle members definitely will be at lower temperatures.

A German support manufacturer, Lisega has a publication that gives temperature distribution in thier clamp supports. You may be able to contact the local Lisega support supplier to obtain it.

Regards,

Ibrahim Demir

Ivan,

I believe when you said "clamped with rotational restraint" = friction grip clamp? As the temperature range is very high how do you assure the constant grip throughout the cycle given thought that the pipe matl and support matl may be different?

Why not thermally insulate(high performance ceramic/polymer or composite?) the interface between the pipe and the clamp as long as it satisfies the operational integrity of the support. In this case you might be able to use usual material or little higher grade and save on mass supports.

Just a thought!

Regards,
Siddharth.

Sid,

The clamped saddle with rotational restraint that is integral to the pipe is the same as the friction grip clamp with the pipe attachment. Most of the steam pipes at that temperature moves longitudinally and laterally. In case the lateral force that the pipe is under is larger than the frictional restraining forces (especially if a guide is in use) there is always a tendency which cause rotation of the clamped saddle around the pipe. Additionally the grip around the pipe can not be guarantied for all time.
To eliminate the rotation, the clamped support needs to be restrained on the pipe to overcome this effect.

Heights of standard clamped saddles are very tall, therefore the moment arms are large for these saddles and the overturning moment can easily pass the grip moment under the friction force underside the base plate.

I agree that there is no difference in the response between the friction grip clamp and clamped saddle with rotational restraint if the pipe moves longitudinally only. However I have seen some companies do add longitudinal shear restraint as well in case the grip can not be provided all the time.

Regards,

Ibrahim Demir

You did not state the pipe size, but a pre-insulated support is another option but will not be "cheap" either. See "Pipe Shields" type shoe from Piping Technology & Products, Inc. At least the hardware will be Carbon Steel.

Compare the proper options, but for High Temp systems the real considerations should center on what is fit for service.