Minimum Temperature Pipe Class Boundary

[nikolastrojman]

Hi,

can you please share your thoughts on the following matter.

I came across a piping spec from client for which a minimum design temperature boundary was defined at -10 °C. Accompanying design pressure at this temp. is 41.4 barg.
The class is based on ASME standards B31.3, B16.5 etc. The material is ASTM A312 Gr. TP316L and it as rated at 300#.

What I´m trying to understand is why below this temperature of -10°C pressure rating suddenly drops to lower values e.g. at -29°C it is 12.1 barg??
There is a note inside the class that use of this class below -10°C is foreseen only for short periods and with a reduced pressure rating. Why??

In the document explaining the way the class was assembled (actually from notified body) it says:
For start-up / expansion procedures / low ambient conditions (short-time procedures) the minimum design temperatures are -29°C with reduced Pressure-
Temperature-Rating according to the requirements of ASME B31.3, Fig. 323.2.2B.

I tried to understand how the value of 12.1 barg was calculated at -29°C using ASME B31.3 323.3.2B but without success

Any clues what is this all about?

 

[LittleInch]

Someone I think hasn't interpreted the graph correctly or they don't know so they have used the worst case design reduction stress of 0.3.

That section of the code - section 323.3.2 is quite complex and has many clauses, but I think if you take 0.3 Df reduction you don't have to impact test so they've taken the easy option. I think.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[david339933]

I wouldn't search B31.3 too hard.....this is like trying to find a Leprechaun.

 

[MickMc]

Seems strange one to me as for there is no change in allowable pressure under 38°C (41.4 barg 316L) and fig 323.3.2b not relevant for SS in my view as impact testing not required.

It may be that your piping specs require additional measures e.g. valve testing, packing at temperatures lower than -10 which may be waived for short term conditions and the statement related to 323.3.2b would be for CS/LTCS to utilise stress ratio for the reduced pressure at lower temperatures.

 

[XL83NL]

Also, if the stress ratio would apply, I’d apply it to something that actually ‘sees’ a stress ratio, i.e. something with a wall thickness. Like a pipe or a bevelled end of a flange, not the actual flange itself which experiences a flange rating.

Huub
- You never get what you expect, you only get what you inspect.

 

[GD2]

For SS TP316L Fig 323.3.2b may not apply. A312 TP 316L and A182 F316L material can be used up to -254C with design pressure 41.4 barg. I am not sure why the MDMT was limited to -10C. Yes, there is criteria for impact test requirement but it shouldn't limit the allowable stress/design pressure up to -254C.
Check if there is any non SS components in the piping system that limits the MDMT and therefore reduced pressure/stress.

GDD
Canada

 

[XL83NL]

The -29 might be related to stud bolt material (e.g. B7), but that a I’ll doesn’t explain the reduced pressure.

It’d be helpful would come back and provide input, or at least show some appreciation for the replies provided so far.

Huub
- You never get what you expect, you only get what you inspect.