Design Criteria Buried Steel Piping 1

[steve1]

How appropriate is a stress based criteria for the design of buried piping? I am reviewing a design of a casing pipe (30 inch diameter) that will be jacked 7 feet below a RR grade crossing. The link below, which has been mentioned in other threads here, presents a stress based criteria for the checking of buried steel piping. The suggested acceptance criteria presented in Appendix A specifically notes that an allowable deformation or strain is not applicable to earth loads (static, live, surface impact).

This is in direct contradiction to the RR specs that the design was based on. The RR specs are based on an allowable deformation of 3% of the casing pipe diameter.

As it turns out the casing pipe meets the RR spec but fails the through wall bending criteria.

Should we require thicker and higher grade of steel to meet the guidelines below?

http://www.americanlifelinesalliance.org/pdf/buried_pipe.pdf

 

[CRG]

I don’t believe your referenced guide is the most appropriate for RR crossings. I would recommend that you take a look at API RP-1102, “Steel Pipelines Crossing Railroads & Highways.” This is the most relevant guideline for this that I have seen.

Is there a reason why you are not using API RP-1102 ?

 

[steve1]

CRG

I will be ordering API 1102 (just need a PO from my employer). I'm just trying to get a handle on the referenced standard. It s the only one that I have seen that presents an allowable stress criteria. Wasn't sure if it superceeds deflection based criteria.

 

[stanier]

You should also cover buckling, deflection and strain in your analysis

 

[steve1]

According to this article I found in the ASCE data base

http://www.pubs.asce.org/

http://WWWdisplay.cgi?0411969

the modified Iowa equation is being misused as a design equation to determine the thickness of buried steel piping. I have not read the article, just the abstract. Has anyone read this article, and if so could they comment on it? The modified Iowa equation is used as the basis for through wall bending stress that is the subject of my original post.

 

[dicksewerrat]

you have to use the Iowa only for the 3% deflection. there are some flexible pipe formula in ASTM 1216 in app. X. that may help you. you will have find the actual load on the casing. Use the heavier RRload. I think it is E-80 and gives a live load of 13 psi with soil density of 130#/cf

 

[Hookem]

API 1102 5th Edition is based on Spangler; API 6th Edition (current) is based on research by GRI/Cornell University. One should do the calculations per this methodology by hand the first time to understand, but thereafter by excel spreadsheet or software program. Or, contact a consultant.