Re: Underground Piping

From: <Gordon.Reddek@Alcan.com>
Date: Wed Jun 02 2004 - 21:29:00 EDT

Dear Thanks,

The criteria for buried pipe depends on the code that has jurisdiction over the facility you are designing. These days one seldom designs a pipeline from first principles, you have to design to the requirements of either a national, or international standard. As always you guys give insufficient information to give good advice. What are we talking about here. High pressure steel oil or gas line, plastic or a concrete sewer? What is the diameter? two inches or six feet? For what it is worth: 1) Steel high pressure oil and gas lines under roads with normal traffic are normally buried with 1200mm cover, that means from the top of the pipe to the road surface.
2) If the road is to be subject to abnormal traffic, like trucks carrying heavy equipment, one normally buries the pipe deeper, or , the pipe runs in a culvert designed by civil engineers to take the load, or a slab is cast over the pipe to distribute the load to the ground on both sides of the pipe.
3) Very large diameter low pressure lines like sewers require special treatment. That is the area of a specialist and you should not touch it if you are not qualified.

Regarding bedding material. The soil below the pipe is commonly called bedding and that above the line is called shading. Normally it has to surround the pipe with a layer of at least six inches (or 150mm). The specification normally calls for clean loose sand free of stones and extraneous material. Some specs may even nominate a sieve size that the sand must pass through however it is not uncommon to see clauses like "the sand may contain stones of a rounded shape and with a diameter no greater than (say) 10mm." The details will depend on the pipe coating. If the pipe is a steel pipe coated with a fairly soft coating the spec will have to be stringent to protect the coating from damage by the bedding and shading material. If the pipe is a concrete monster you would most probably call for a loose sand bedding so that the pipe can be levelled properly and shading with the excavated material provided the lump size is on average no greater than (say) 100mm. What you specify depends on the pipe you are installing.

Sure you can join pipe under roads. If you are running gas or some other dangerous material you will not want a leak there so one tends to be more stringent regarding joints in that area. Some Authorities may require that the line under a road is jointless, however in general pipe codes require the pipe in that sort of area to be thicker so that they are more lightly stressed. Flanges are generally not allowed on buried installations so I would expect that a full penetration butt weld which is subject to 100% NDT would be considered to be acceptable.

Once again, you must find out what code governs the way you design your line and you must be guided by the requirements of that code.

Gordon Reddek
Specialist Mechanical Engineer
Alcan Engineering, Level 3, 443 Queen St, Brisbane, Qld 4001, Australia. Tel: +61 7 3328 6424
Fax: +61 7 3328 6990
Email: <a href="/group/PipingDesign/post?postID=NYjT0bPU_-K8gZdc0Cv7WCRNKmIz0hoFfC1PKtXjh4HtHhNBX54V8sqKlMwoW2lg0t3lVRi8gUC3wrQf9NfBlA">gordon.reddek@alcan.com</a>

"cckla" <cckla@pd.jaring.my> 02/06/2004 03:40 PM
Please respond to
<a href="/group/PipingDesign/post?postID=CkZc3jWb6DnLzzF0aeXXPxLXEtxo8qcqPB24X4bokje8fYClfasSSaamyO2k2G1yBwZto7I_NciTLP84fCljhsDSlQEXPg">PipingDesign@yahoogroups.com</a>

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Subject
[PipingDesign] Underground Piping

Dear All Specialists,

1. What are the criterias, which determine the depth of the underground pipe ?
2. What should be considered in the selection of soil for the underground pipe trench ?
3. Should there be any joint under the crossing road ? If yes, what will be the suitable joints ?

Thanks

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Received on Wed Jun 02 21:29:00 2004