I am doing a stress analysis of a existing HP steam line. In here over a period of time due to vibrations, upset and thermal expansions the support are damaged.

I have checked stress point of view as per the existing site condition the anchor, support span are within the limit as per ASME 31.1.

Now the problem is clamp with shoe support are over displaced and in some portion the clamp gets dismantled. Kindly advice clamp with shoe support is advisable or not for HP steam lines.

Is your line connected to a reciprocating machine?

Corrado Vannella
www.vannella.com

Thanks vannella for your quick reply,

These steam lines are connected to HP steam turbines.The pipe design temperature is 535 Deg Celsius and design pressure is 127.5 Barg.

Dear Kart89

Clamp shoe support type should be OK. For high temperature due to high axial pipe thermal movement extended length shoe required to ensure shoe support do not fall down from structure. Probably stress engineer who perform analysis before forgot to recommend extended length shoe in selective locations where there is high axial displacement as per stress calculation. For high temperature line please ensure there is no high lateral displacement that will possible hit nearby pipe or equipment.

Regards

Habib

Thanks for your advance reply

I have seen many clamp supports are very old and loose-fitting (clamps are dismantled) condition, so kindly advice me any other shoe support is better than the clamp with shoe support and also any other shoe supporting standards for high pressure steam piping (turbine piping).

Do you have the pipe stress analysis in hand to check the type of the loading at support locations?

Comparing the B31 span length with the available piping may give you misleading information. First you need to obtain the support loading and check if the support nature can take the loads. From my experience some companies ask the stress analysis to one person and ask the support selection another without a proper communication between them. Some cases the selected support (mainly the clamped shoes) will rotate and lift of the pipe under the lateral guide loads since there is no torsional connectivity other than the clamping friction which may not be sufficient to overcome the rotation.
None can comment on the problem without seeing the analysis loads and the drawing of the supports. After obtaining these you may do some additional calculation if the calculation is not available.

Normally, supports with friciton are fobidden for main steam, cold reheat, hot reheat and LP steam, deviations to this require client written approval, this is the thumb rule from one famous power plant company.

Thanks for your reply Ibrahim,

My client does not have the stress analysis report from their side. When I went to site for surveying the lines I found many shoe supports have been not resting in the structure the shoe supports have been over displaced and the pipe is directly resting on structure. In many of the hanging spring supports also the hangers have been displaced. I think so this can be rectified by giving proper shoe length based on analysis.

As you said earlier reply, I also found some shoe supports have been rotated due to lateral load. Kindly you to advice me which shoe support is suitable for high pressure steam piping

We have attached the two types of shoe supports as shown in type-1 can I go to type -2.

The condition of the piping and pipe supports are worst than I expected. The piping works in the creep range, you might expect many problems in the piping with these conditions.

I would normally ask your client to contact the maker company to correct their job after seeing the conditions of supports. The selected supports and loss of supports tell me that the pipe support engineer does have no clue on the high temperature power piping.

Do you know how old the plant is?
Is the plant still working with these support conditions?
Does your client have full record of the temperature and temperature cycles that the piping exposed?

I expect the pipe lost its straightness gradually due to the random support loss at many locations, perhaps there are local deformations and creep at some locations. I guess the piping needs to be checked metallurgical, physically before putting into service. Sometimes the pipe may need full or partial replacement due to the creep. I would expect the spring hangers fully compressed and do not do their job either.

If the above is all adequate, piping can still work within the life time, and you may guess the thermal expansions (displacements at supports)and the forces on the supports (you must need to get these from the designer company, otherwise your effort will be worthless and you will be responsible for the future problems), I would suggest, consult a reputable vendor to select and implement the supports for the displacements and forces. Additionally the control of thermal axial displacement may be required by considering the thermal displacement at each support location.

All we can offer you is a guesswork, will not go anywhere unfortunately.

Good luck.

You should also check that the pipe support shoes and clamps have been made from a material suitable for the high temperatures. If they are only carbon steel, then they may have yielded and this may have contributed to the state they are in.