Piping reccomendation- ERW Welded C.Steel Suction Line or Seamless C.Steel

[AliCanGonc]

Hello all

I have a design and build application with r407C. The system will have 150mmOD suction lines and will need to use carbon steel.

In literature(american) it is suggested to use SCH40(similar to natural gas pipes interms of pipe thickness). I check the pipe properties and find out that the operational allowed pressure is 45Bar,testing pressure is 70Bar for Schedule40 pipes.

I do not want to use an overqualified piping for the job, but do not want to underestimate the job either. Highest pressure r407C will go in the system is 8-10bar max. Standard Electric Resistance Welded pipes in the market have properties of 25Bar operational pressure allowances(which seems more than enough.

I read that in ammonia systems most of the time suction and discharge lines are used with seamless carbon steel. I do not understand why especially seamless .

My questions are:

1)Can i use ERW(electric resistance welded) carbon steel pipes instead of seamless carbon steel pipes?.(I am worried if sudden changes in the temperature may create microcracks on the welded area after a period of time maybe?)
2)Should i use regular thickness (25bar) pipes instead of 40bar pipes.

Thank you for your time.

[Josip]

Hi, AliCanGonc

Hello all

I have a design and build application with r407C. The system will have 150mmOD suction lines and will need to use carbon steel.

In literature(american) it is suggested to use SCH40(similar to natural gas pipes interms of pipe thickness). I check the pipe properties and find out that the operational allowed pressure is 45Bar,testing pressure is 70Bar for Schedule40 pipes.

I do not want to use an overqualified piping for the job, but do not want to underestimate the job either. Highest pressure r407C will go in the system is 8-10bar max. Standard Electric Resistance Welded pipes in the market have properties of 25Bar operational pressure allowances(which seems more than enough.

I read that in ammonia systems most of the time suction and discharge lines are used with seamless carbon steel. I do not understand why especially seamless .

My questions are:

1)Can i use ERW(electric resistance welded) carbon steel pipes instead of seamless carbon steel pipes?.(I am worried if sudden changes in the temperature may create microcracks on the welded area after a period of time maybe?)
2)Should i use regular thickness (25bar) pipes instead of 40bar pipes.

Thank you for your time.

Here we are ... something to read ...

http://www.baltimoreaircoil.com/engl...brary/file/553

Because copper and copper-bearing materials are attacked by ammonia, they are not used in ammonia piping systems. Steelpiping, fittings, and valves of the proper pressure rating are suitable for ammonia gas and liquid.Ammonia piping should conform to ASME Standard B31.5, Refrigerant Piping and IIAR Standard 2, which states the following:
1. Liquid lines 1.5 inches and smaller shall be not less than Schedule 80 carbon steel pipe.
2. Liquid lines 2 through 6 inches shall be not less than Schedule 40 carbon steel pipe.
3. Liquid lines 8 through 12 inches shall be not less than Schedule 20 carbon steel pipe.
4. Vapor lines 6 inches and smaller shall be not less than Schedule 40 carbon steel pipe.
5. Vapor lines 8 through 12 inches shall be not less than Schedule 20 carbon steel pipe.
6. Vapor lines 14 inches and larger shall be not less than Schedule 10 carbon steel pipe.
7. All threaded pipe shall be Schedule 80.
8. Carbon steel pipe shall be ASTM Standard A 53 Grade A or B, Type E (electric resistance welded) or Type S (seamless);or ASTM Standard A 106 (seamless), except where temperature-pressure criteria mandate a higher specification material.

Standard A 53 Type F is not permitted for ammonia piping.
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https://ref-wiki.com/technical-infor...nt-piping.html
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The best is to use seamless pipes either SCH 40 or SCH 25
at least that was the rule in my time ... today a lot of rules are upside down ...


Seamless pipe price is one thing, but if you have a leak and loose refrigerant ... then you need to replace the pipe/s ... refrigerant and ... price of the damaged goods ... quite expensive

all is about system tight ... with seamless pipes no problem with seam cracks at low
temperatures ...

but you can try with ERW pipes ... we usually use them only for water ...


Best regards, Josip

[AliCanGonc]

Dear Josip,

Thank you for your detailed message. I also checked before the baltimore piping leaflet.

8. Carbon steel pipe shall be ASTM Standard A 53 Grade A or B, Type E (electric resistance welded) or Type S (seamless);or ASTM Standard A 106 (seamless), except where temperature-pressure criteria mandate a higher specification material.

according to this document ERW pipes are also acceptable? I believe there is no such schedule as Schedule25 in general pipe sizing charts. As mentioned before for a 6" pipe for instance there is no lower Schedule than SCH40 in american standard pipes.

SCH40 for 6" pipe wall thickness is 7,1mm.
The one that i intend to use has 5mm thickness.

You mention about cracks on seam connections, did you face such issue before? Is this really a risk? That is the main case actually for me rather than pressure norms of the pipes.

Regards

[Josip]

Hi, AliCanGonc

Dear Josip,

Thank you for your detailed message. I also checked before the baltimore piping leaflet.

8. Carbon steel pipe shall be ASTM Standard A 53 Grade A or B, Type E (electric resistance welded) or Type S (seamless);or ASTM Standard A 106 (seamless), except where temperature-pressure criteria mandate a higher specification material.

according to this document ERW pipes are also acceptable? I believe there is no such schedule as Schedule25 in general pipe sizing charts. As mentioned before for a 6" pipe for instance there is no lower Schedule than SCH40 in american standard pipes.

SCH40 for 6" pipe wall thickness is 7,1mm.
The one that i intend to use has 5mm thickness.

You mention about cracks on seam connections, did you face such issue before? Is this really a risk? That is the main case actually for me rather than pressure norms of the pipes.

Regards

Baltimore is coil manufacturer and maybe not too relevant ....
for refrigeration I believe it is better to check ASHRAE ...


Sorry, my mistake no SCH 25 but SCH 30 .... we used before in Europe ... but later on everyone accept SCH 40 ... in my opinion wall thickness is too big for refrigeration purpose ... but pipes we paid by weight


Never faced cracks .... because we did not use welded pipes ...

faced crack on seamless suction pipe on ammonia plant ...(strange ... like life sometimes)
pipe was isolated and leak was not easy to find ...
... that was in engine room where you can have small leaks on many places ....


It is your decision which pipe you'll use ...
for me as an old school engineer welded pipes
do not exist within refrigeration plant not even for water ...

Best regards, Josip

[AliCanGonc]

Dear Josip,

I found the same literature of baltimore in ASHRAE 2014 Refrigeration Handbook- It's a direct copy-paste from ammonia piping guideline.

I respect totally your experiences and rule of thumb approach on the matter but as engineers i believe we should not overestimate/underestimate the designs we make.

Today i got a call from a quality engineer from one pipe producer, they indicate that each pipe is pressure tested(x2 of the value of PNorm of the pipe) to see check any leakages on the seam.

That already clears the possibility of any leakage on the seam so unless anyone else thinks otherwise i think that i should go with SCH30(as also suggested by you) ERW pipes.

thanks a lot

[Josip]

Dear AliCanGonc,


No problem I accept your decision,
maybe not agree completely with your stand ...

Manufacturers are prone to promise almost everything to sold their goods ...
but that is OK ... risk is ours

I believe you need only one shorter piece of suction pipe
so little higher price must not be a problem or...

It is not a question of pressure ... welded pipe can bear it without problem ...
but what about material i.e. weld fatique due to temp change ...
not sure what will be after a while ...

Anyhow, I wish you good luck with your project.



Best regards, Josip