Stress analysis of Buried piping Inside Refinery area

Hello everyone,

Which code shall be followed for Buried / Under ground piping analysis laid within refinery / petrochemical unit ??

As there is no specific guideline (Allowable / Induced stress criteria, Failure theory)given in B31.3 code for buried piping analysis, Can Code like B31.4 / B31.8 be used for analysis of buried / underground piping laid within refinery / petrochemical unit ???

Depend on pipe material, reference code can be changed...

I have this query because our client is asking to perform stress analysis of Underground / Buried piping laid within refinery area.

On performing analysis with Code B31.3 and ALA method, it is showing expansion stress failure at many locations.

MOC of Piping is API5L.

As per my understanding, Underground / Buried piping is not in scope of B31.3.

I also understand that buried piping within refinery does not comes under the definition of PIPELINE. However, still I feel application of Code B31.4 (Liquid service) is far more relevant than code B31.3 for analysis.

Mr.Dave Diehl / Mr. Richard Ay / Experience Stress engineer ,

Please share your experience, if any, for above said subject.

Generally buried portion of piping will be stress analyzed as per ASME 31.4 or ASME 31.8 depends on the service of the pipe. In piping GA please go through if there is any spec brake and changes from 31.3 to 31.8. If there is a spec change and pipe material is API 5L GR xx (except API 5L GrB) it’s a pipeline.

If there is no spec brake and it’s a being underground only for road crossings. Then try to model pipe sleeves with (Y+GUIDE) in ring locations.

Most of the elbows will fail in expansion case from maximum to minimum temperature in UG portion, if you are not defining the case properly.

Simply because a pipe is buried does not indicate that B31.3 does not apply.

In my oppinion strictly speaking when the pipeline crosses the refinery's battery limit, it must be designed according to B31.3, this is due to the risk of the pipeline failure and its possibility to affect the other equipment of the plant, however if the Duct ends in an area of pig receivers, the designer may consider as part of the pipeline this part, and consider code B31.3 from the first valve that goes to the interconnection inside the plant, it is very important to evaluate the risk of a failure in the pipeline and its affectation to take the decision.

This is typically based on the discretion of the governing authority or authorities.

For example, in America, if your line is between two facilities, you're under the jurisdiction of the Department of Transportation, which generally specifies B31.8.

However, within the refinery, there may be no governing body dictating how you design it - just that you must ensure it'll work, and therefore B31.3 becomes the typical go-to choice.

I understand that Cross country pipeline / transportation pipeline only can be designed as per B31.4 /B31.8.

But I am beat confused for usage of Code B31.3 for Underground piping within refinery area because there is no specific guideline or formula given for buried piping in B31.3 which can simulate the "RESTARAINED" or "UNRESTRAINED" piping. Also from the scope of B31.3 , It is not clear that buried / underground piping can be designed as per B31.3.

However , thank you all for sharing experience / knowledge / understanding.

If anyone do have any other thought / understanding can share please, that will be really helpful.

ASME B31.3 Interpretation 21-07 clarifies that ASME B31.3 applies to buried piping also.

ASME B31.3 does not give guidance or requirements for buried piping, but it does give the minimum requirements for all piping. B31.3 300(c)(5) indicates that unusual requirements for a particular service need to be specified in the engineering design.

Piping can be designed to and meet B31.3, but also satisfy additional requirements (such as for buried service) that the engineer specifies. You can look to B31.4 or B31.8 for ideas on what additional requirements to specify, and also B31.1 has a Non-Mandatory Appendix VIII Procedures for the Design of Restrained Underground Piping that may be helpful.

Thanks for sharing Mr. Clark, It really helps.

Similarly with B31.1 VII-5 ALLOWABLE STRESS IN BURIED PIPE, your B31.3 calculation may consider SA + Sh as allowable.