ANSI Pipe Spec - Low Temperature Materials at Larger Diameters

[JABoomer]

Hello,

I am currently helping my company revise our ANSI pipe specs.

What we are finding is that for normal-temp specs (both sweet and sour service), some companies have chosen to specify low-temp materials for larger diameters. For instance, B-spec will switch to low temp for 24 NPS, and C-spec will switch to low-temp materials for 10 NPS and above.

What's interesting, is that some companies specify low-temp for pipe only; some for pipe and fittings; some pipe, fittings, and flanges; and some specify all of pipe, fittings, flanges, and valves to be low-temp above a certain diameter.

Does anyone understand the reasoning behind specifying low-temp materials for larger diameters in normal-temp specs?

Thanks, JA Boomer

 

[Dhurjati Sen]

Dear JABoomer,

In the yester-years, large diameter pipes were made from plates. Now, we get seamless for most large diameter pipes. So the issue was how to control the mechanical properties (specially impact toughness). Specifying low temperature materials for large diameter pipes ensured a good control on inclusion content.

Hope you get the reasoning.

Regards.

DHURJATI SEN

 

[mk3223]

IMO, it may be because the material availability of the components, which depended on the suppliers in the region at the time of the project.
While it's confusing, the different material of the piping components should be all suitable for the process service conditions of the specs.

 

[GD2]

JABoomer,
Let's start with what construction code was followed for design of the plant? Then what service the piping class to be used and what was the MDMT? Once these are known, then it becomes pretty easy to follow the code requirement.
As the codes stipulates the minimum design requirements, many Owners/Projects want to play more conservative by specifying LTCS even where it is not necessary.

GDD
Canada