Ductile-Brittle Transition temperature for API 5L X70 Pipeline
Ductile-Brittle Transition temperature for API 5L X70 Pipeline
(OP)
For a proyect I'm working in the pipeline was bought with a charpy impact test at -10°C with a minimum absorbed energy of 60J.
The problem we have is that according to the process department during pressurisation with a big differencial pressure the temperature might go as low as -70°C.
If the pipeline material is impact tested with this new temperature (-70°C), ¿The minimum absorbed energy should still be 60J to comply with the API5L code?
¿What other method do I have to ensure that the material will not be embrittled due to the low temperature?
Thank you very much for your comments.
Francisco
The problem we have is that according to the process department during pressurisation with a big differencial pressure the temperature might go as low as -70°C.
If the pipeline material is impact tested with this new temperature (-70°C), ¿The minimum absorbed energy should still be 60J to comply with the API5L code?
¿What other method do I have to ensure that the material will not be embrittled due to the low temperature?
Thank you very much for your comments.
Francisco





RE: Ductile-Brittle Transition temperature for API 5L X70 Pipeline
At the end of the day people have control over rate of pressurization and of the amount of J-T cooling that is acceptable. This seems like a problem that should be solved via operating procedures, not materials changes.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Ductile-Brittle Transition temperature for API 5L X70 Pipeline
http://www.eng-tips.com/viewthread.cfm?qid=400253
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Ductile-Brittle Transition temperature for API 5L X70 Pipeline
It will help if you can post a sketch of this system with this repressure bypass line.
RE: Ductile-Brittle Transition temperature for API 5L X70 Pipeline
Here's a sketch of the system:
There is a limitation with the available time to carry out the pressurization maneuver, so it has to be minimized.
Another issue is that some people have the opinion that one cannot carry out a controlled pressurization through a plug valve (like the ones in the sketch)
¿What's your opinion in using this kind of valves for this task?
RE: Ductile-Brittle Transition temperature for API 5L X70 Pipeline
That said, you can successfully pressurize the downstream piping through that valve arrangement. It is just writing a procedure that is sensitive to the capabilities of the valve (mostly that you get 100% flow at about 18% open so you can't open them much in this service or your mass flow rate and dP will lead to very cold pipe).
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Ductile-Brittle Transition temperature for API 5L X70 Pipeline
If a high pressure situation can result on downstream facilities during this repressure operation, then automated safeguards against overpressure would be required for this bypass line.