Limitiation on OD for A333 Pipe

[WJS1962]

My Client has a limitation of 14" OD for A333 pipe in their pipe spec. Pipe that is 16" or larger shall be API 5L. (Natural gas pipeline, low temperature carbon steel service.) Any ideas as to why they might limit the OD of A333 to 14"?

 

[EdStainless]

Two thoughts, perhaps their normal seamless vendors can't push anything larger than 14".
Or maybe they can't meet impact requirements in the larger sizes.

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[LittleInch]

No idea why they want A333 grade?? Anyway for natural gas service API 5L is good for all sizes and temperatures you're likely to get and if its good enough for >14" then it's surely good enough for lower sizes? You only really need A333 grade 6 for < -45C.

It's probably something to do with seamless / welded, but maybe only applied to one project or location, but someone just copied it for the next project. That's the problem with these sorts of specs which no one then knows why it was done that way, but no one wants to change it.....

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[WJS1962]

Its a northern, cold-weather site with a -40F ambient. Its pipeline quality natural gas, so it will be dry. Thus, there is no reason to insulate it. Therefore, the pipe will be exposed to the -40F environment, which is what lead me to assume the need for low temperature carbon steel, A333 Gr 6, which is good to -50F.

For the CL600 pipeline, one can use A333, but the SMYS (35,000 psi) is lower than for API 5L PSL2 X52 (52,200 psi) or X65 (65,300 psi). So the required wall thickness is more for A333 than for X52 or X65. I don't know cost, but I bet X52 or X65 is higher priced than A333.

I've digressed a bit here, but ultimately, I'm just trying to figure out why they have this 14" OD limitation on A333.

 

[GBTorpenhow]

I would guess that this is because Grade 6 pipe can get unreasonably thick, especially if required to stick to the 20% SMYS distribution design hoop stress limit. At some point the thickness you need in A333-6 is such that it becomes more cost effective to go to thinner wall API 5L high yield pipe and add supplemental low temperature impact testing requirements.

 

[LittleInch]

Above ground pipe?

but yes at 35,000 SMYS above 14" you're going to end up with some pretty thick pipe.

Not sure about the 20% figure though. where does come come from GBT?

double guessing someone elses spec is not easy....

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

 

[GBTorpenhow]

The 20% SMYS is a 49 CFR 192 thing here in the US. Only a guess that OP is in the USA based on use of F vs C. To qualify as 'distribution' vs 'transmission' a pipeline must be designed for no more than 20% of SMYS. Distribution has more relaxed requirements for welding, inspection, and whatnot as it is really meant to apply to street level distribution mains and the like. Operators will sometimes classify a pretty significant lateral pipeline from a large regulator station to their customer as distribution to sidestep some of the 192 requirements for transmission pipelines. In northern climates this makes the A33-6 wall thicknesses required to get up to Class 600 design pressures simply unreasonable.

About material cost, for the same thickness the 5L high yield might be more expensive than A333-6, but the cost difference between say Grade 6 Sch 80 and X65 STD w/CVN might be close to a wash. Would have to factor in the increased welding cost at the higher wall thickness, etc.

 

[WJS1962]

Thanks everyone. I'm not sure I see a clear answer. But it could be that they have determined that for CL600 pipe that is >=16", that it is more cost effective to use thinner walled API 5L with an impact testing program than thicker walled A333. (That appears logical to me. I just don't have any actual cost data experience to back it up.)

 

[LittleInch]

Who said distribution?

At class 600 sounds more like a high pressure transmission line to me, but I get the CFR thing.

But if this thing is buried it won't get to -40F or C surely?

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

 

[WJS1962]

As stated above, its bare steel that is exposed to the -40F ambient, so NOT buried. If it were buried, I wouldn't be looking at A333.