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How to calculate the saddle area for Screw Anchor in Buoyancy Control?

How to calculate the saddle area for Screw Anchor in Buoyancy Control?

How to calculate the saddle area for Screw Anchor in Buoyancy Control?

(OP)
Hi,

I've stucked here for couple days now... A NPS 16 pipe with PUR insulation and PE Jacket needs to be laid down in some wet and muskeg area, so buoyancy control will be necessary. We conditionally choose to use screw anchors for protection. But because of the PolyUrethane insulation layer out there (the Polyethylene jacket can be ignored since its thickness and flexible property), we need to calculate the minimum area of the saddle for avoiding crushing on the insulation layer.

For the worst scenario, like before we bury the pipe, there is no soil stress up there, so the only two stresses working on the pipe will be Net Buoyancy (Buoyancy minus Pipe weight) and the force by screw anchors, is that correct?

And the question is, imaging the saddle is rectangular and covered the top half (like semicircular) of the pipe, what is the real affecting area or say, interaction area on the pipe? Since if we assume the force from screw anchors is going down vertically, all the horizontal component force will be balanced and only the force going down left.

And I know there are lots of other stresses like shear stress, hoop stress or bend stress out there, but based on this Front-End design, we try to make it as easier as possible to get the best result for customer with minimun cost...

Please help! thanks guys!

Sheldon

RE: How to calculate the saddle area for Screw Anchor in Buoyancy Control?

I'm not sure you have provided quite enough information on pipe, service, soil/burial or other pertinent conditions (for those, with I'm sure much more experience than I in this specific area, to help much!) See e.g. http://www.ogj.com/articles/print/volume-93/issue-.... Per at least this article it sounds like such systems, at least up until that time a few years ago, were not used much by these folks for buoyancy control on smaller pipelines (that it appears could involve more effects than postulated above).

RE: How to calculate the saddle area for Screw Anchor in Buoyancy Control?

While I haven't seen him in a while, I think Randy Robertson of Cyntech (who wrote the article I provided link to above) is a good guy and I suspect knows a good bit about screw anchors and muskeg. He may be a good contact, and if he could not help you with the specific application to insulated pipe, I suspect he could direct you to someone who could.

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