Pipe shoe and saddle design basis or guide 1

[IFRs]

I'm looking for a resource that covers the design of pipe shoes and saddles. I've seen many variations in materials and especially welding details. I figure it's about time I learned how these items are designed. Any help would be appreciated!

 

[4Pipes]

I like DSB123's words. A rather cutting but very apt use of "come up with" rather than "design".

 

[saplanti]

Shoe type supports are intended to be used under vertical loads ( radial direction ) with a thermal displacements in the longitudinal direction of the piping. This is basically supported by BS 3974art2-1978 Appx A.8 an extraction is in the attached document called "Collection.doc"- I interpret the statement in that clause the expected bending moment is only in the longitudinal direction of the pipe. In case there is a large guide load exist the capacity of the shoe has to be investigated. This standard gives very good information how to design and what needs to be done for the anchor and guides.

There are two available source to do manual calculation, WRC107 and BS5500. Both have limitation on the attachment dimensions. This is very clear in WRC107 Table 7 & 8 with the ratio of b1/b2 which is limited by 0.25 - 4. Remaining outside of these values ends up with wrong results which are not supported by the tests behind the WRC107. Similarly, BS5500 Appx G has curves (Figures G6 - G13) to be used for the calculation of local stresses. The calculated coefficients are most of the cases outside the curve values.

WRC198 has similar method to WRC107. It uses similar limiting values. In our case b2 value is not within the limit ( 0.05 - 0.5 ).

ASME Sect I, AS 1228 and AS 4041 give guidance for the application of lug (in this case shoe) supports and allowables on the piping in radial direction which includes bending moment action in the longitudinal direction only. There is no allowable load or stress definition available in the circumferantial bending for the long plate attachment (such as web of T-bar) for local stresses on the pipe. If there is large lateral load or guide loads on the shoe, the shoe needs to have a T-bar ( or double web shoe depending of the loads) with end flanges ( or stiffeners in lateral directions) to transfer the loads onto the pipe and reduce local stresses. This has to be supported by calculations on pipe side for local stresses and shoe (structural calculation for plates and welding) itself.

As result: I do not recommend the use of shoe type support with guides in the piping applications under the large loads (who knows which load is adequate without a proper calculation with other load combination?). They are useful to take radial (compressive/tension) vertical loads, longitudinal movements, and longitudinal bending moments within the capacity which have to be again calculated.

Last 20-25 years, the support manufacturers concentrated on producing non-integral supports to overcome the local stresses on the piping not to introduce localized circumferential bending moment on the piping under the lateral movement or guiding shoe in lateral directions. Some cases this is impossible due to the space around the pipe. So, there is a need for the special and simple supports to design and manufacture. Please remember that the non-integral clamped shoes DO REQUIRE some integral shear attachments agains the rotation and locating in the longitudinal direction (some can reject this idea, I agree with them if the loads are small or the low friction pads used). Do not believe that clamping forces can overcome the rotation of non-integral shoe under the guide loads either.
In case there is only a large longitudinal movement on the piping a T-bar cradle or double T-bar cradle support with/without low friction slide plates can be used.

I would like to recommend anyone who is interested in pipe shoe supports to look at the web site of the support manufacturer "Piping Technology & Product". The Shoe Decision Tree in this website can give a good idea about the shoe supports. In this tree you may see how and when they are used and the capacities of the supports with their load directions.

http://www.pipingtech.com/products/ptpcat/pipeshoes/decision.htm

Kind regards,

Ibrahim Demir