Ductile-Brittle Transition temperature for API 5L X70 Pipeline

[franciscobruzone]

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

 

[zdas04]

Pressurize it slower? This is obviously not cryogenic piping or you wouldn't be using API 5L, so your process guys are just calculating the J-T cooling for the max dP and applying the temperature change and a (very high) mass flow rate to get a BTU number that will be removed from the process via cooling the pipe in their simulation. A slower mass flow rate (or a bigger supply pipe) would allow the pressure to be raised without these very low temperatures.

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

 

[SJones]

Snap! (excuse the fracture related pun)

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.

 

[georgeverghese]

As suggested, the low temp effect of these repressurisation operations on big bore pipelines are usually handled by operating procedures carried out under work permit conditions during startup - a small bore low rate throttle valve sitting on a bypass line is used for this - however the bypass line itself may need to be good for these low temps, since velocity is high and metal heat content is low in this bypass line.

It will help if you can post a sketch of this system with this repressure bypass line.

 

[franciscobruzone]

Thank you for you comments,

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?

 

[zdas04]

As I've said here many times, there is no task that can be done by a plug valve that cannot be done much better by another valve technology. I hate the damn things after having lived with hundreds of them in a field operation.

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

 

[georgeverghese]

Typical industry practice is to design the entire bypass line for low temp operation. Usually a block valve and a throttle valve are provided on this bypass at the least. In high pressure situations, use a DBB in place of a single block on this bypass.

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.