Selecting Piping Material for Gas

the temperature shows that its cryogenic services. check ASME B31.5 for refrigeration piping.

That's not cryogenic, it's a brisk autumn day in Canada.

The ASME codes do not cover corrosion issues, and nevertheless, this piping with not be B31.5. It is most likely B31.8 (or B31.3 or B31.4); regardless - the OP needs to speak to a materials/corrosion guy.

-30°C = -22°F, which may be cold enough to require special material and/or impact testing; 100 kPa ≈ 14.5 psi; 8 m/s is pretty conservative.

What are C1, C2, C3, iC4, and nC4? How corrosive?

My recollection from my metallurgy class was that in the -40°F area steel started to lose strength. -22°F isn't really that extreme. See it all every winter in North Dakota. In fact, a fellow student recalled breaking a tractor drawbar at -45°F, pulling what would be considered a normal load. His conclusion was the steel drawbar was in a weakened state similar to the Liberty Ships that broke up near Alaska in the early years of WWII.

http://school.mech.uwa.edu.au/~dwright/DANotes/fracture/maritime/maritime.html

This is a curious one

-30°C looks to me like it needs Impact Tested Carbon Steel which I am used to seeing down to -45°C or possibly an alloy steel (2.5Cr1.25Ni) or something like that. Onshore I would be expecting this to be B31.3 as well.

However what is interesting is the pressure. 100kPa (is it atmospheric or gauge pressure) is basically neglible in terms of piping. In the UK a lot of our domestic gas supplied are being replaced with polypropylene. Now we dont get anything like this sort of low temperature - anything below -5°C, -23°F would bring london to a halt - but maybe plastic is the way to go if they have low temp ones as this would obviate the corrosion issues.

C1 etc are shorthand for Methane, Ethane, Propane, isoButane, normalButane etc. None of these are corrosive but the issue with natural gas is always in the detail.

Is there any CO2, H2S or water all of which would give problems.

Is the pipe to be buried?

The domestic natural gas spec in the UK is dry, with almost zero H2S (a few ppm) and tiny CO2 (a few 100 ppm I think) so the main corosion issue is the wet ground in which it is buried.

As someone has stated, you will probably work to ASME B31.3 for plant piping or ASME B31.8 or PD 8010 for an overland pipeline. DNV applies for subsea pipelines. The pressure seems low. You have CO2 there so corrosion may be a problem. API 5L grades will do it and at such low pressures schedule 40 (or even sch 10 or 20) may be OK subject to corrosion. You will also need to consider external forces and moments from the geometry, temperatures, adjacent equipment etc. If this is a preliminary study this may be sufficient. If it is something serious you should have a piping or pipeline specialist company such as Kenetika have a look at it as there will be safety and legal implications.

A couple more thoughts

Are you sure aboutt the pressure as it is very low. This wouldn't be sensible for pipeline transmission but I think rereading your question maybe that was a wrong steer. Many gas lines in process plant have low pressures of the range you gave us BUT

please check the units!!!!

If the pressure is correct (ie 100kPa approximately atmospheric pressure) then depressuring is not an issue.

However if the pressure is above about 7 barg - 700 kPag (please always indicate if pressures are gauge or absolute) then you mayneed to consider the low temperatures when the system is depressured.

WHen a low temp gas under pressure is depressured (for safety reasons) it gets cold as does the piping. Depending on how high the initial pressure and how low the initial temp this can generate VERY cold temperatures which would necessitate using stainless steel classes.