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Dear friends, i am facing a problem that i can not still find the edge.
we want to construct an Nh3 system at -38oC. we want to use ST35.8I as others in Europe do. that material, as the notified body that is going to specify the installation is not accepting it due to fact that it is not specified for such temperatures. we do not want to change, at this time the material.
can anybody give some kind of advice?:)
thank you very much
Kpapa, can u please tell me the ASTM equivalent of ST 35.81 ?
While I am not familiar with the code stated I suspect this confusion is caused by the desire to use impact tested pipe as a means of assuring conformity with low temperature operation.
I suggest you look at either using stainless steel or carbon steel (with the appropriate stress reduction for low temperature operation). Both of these are allowed under ASME B31.5 for refrigerant piping. Hopefully, your piping code will allow something similar to this.
Seamless tubes St 35.8 (I) according to DIN17175 or A192 according to ASTM. 3.1.B mill test certificate is required.
I have searched this material and i found it to be carbon steel. you are correct about impact testing and they must be asking to use Low temperature carbon steel for -38 degree centigrate. Actually ASME code does not allows to use the carbon steel material below -29 degrees and if you are designing vessels as per ASME then they might not accept it.I think , you must be using some german standard and hopefully you might get some relaxation as sited in the german code. Check it out. Actually plate material, used for making vessel , shall also be imapct tested . You can save money by just giving suction line , chiller and knock out drum ( if applicable), valves and fittings of Low temperatur material. discharge line viz can be of normal carbon steel .Liquid line before throtlling can be of carbon steel, because these lines will not experience low temperature .You can even show your past experience which will strengthen your point.
The majority of vessels and piping used here in the US are fabricated carbon steel. The temperature limit is where you have to do some engineering to evaluate the allowable stresses of the pipe wall versus the actual applied loads for temperature lower than the stated temperature limit.Quote:
Originally Posted by Ambrish_bajpai
The request to use seamless pipe is one of these other issues. The stress reduction factor for seamless pipe is better than the factor required for butt-welded pipe like ERW.
The pipe code which is being used should be reviewed to verify you can do the same thing described above.
All of these are topics that need to be investigated. ;)
See if you are mentioning code or standard on your drawings and proposal documents, given to client, than you have to abide by it. Otherwise you can simply follow good engineering practises and can save your money by using carbon steel. Consultants ,generally ,strictly follow standards and they are least bothered about actual conditon that occurs during operation.
It is permissible in US and Europe to get lot coded carbon steel pipe of "ordinary" spec approved for use at temperatures below -20 Deg. F. simply by submitting samples for Charpy test to a certified materials lab. The lab may want to procure and retain and stamp the samples to sustain the continuity, but if all the pipe subject to low temperatures was procured at the same time from the same supplier, you will have a minimum number of lots represented. As opposed to returning pipe already delivered and paying the premium for the pre-certified material, this might be cost effective...And nobody can argue with it very hard, its just post-certification instead of pre-certification and at least in the US is more cost effective when buying large lots of pipe than ordering the stuff having been certified prior to distribution. We have applied this only a few times but have never had even a single coupon fail.
Sterl! you have given me a nice clue for next lot of carbon steel pipe. Will you please tell me the joule energy value at which charpy imapact testing was carried out and pipes were cleared?? This will help me to convince my consultants.
Quote:
Originally Posted by kpapa
Hi,
We have used A214 (ST37.2) tubes at our NH3 refrigeration to condense CO2. NH3 temperature is 33 C. Please see what happened to the tube at the attached photo. Please comment.
sa-333 grade 6 or sa-106 gr -b will be suitable.
But preferably sa-333 g6
we use sa-333 g6 in india; alhough its very expensive almost twice than sa-106
regds
priti
The equivalent standard no. of ST35.8 is ASTM A-106 Grade A,seamless pipe; therefore I don't see any fault in using this type of material for NH^3 applications at -38°C based on ASME std. B31.5 and IIAR std.2 codes.
When we say very low temp. systems in industrial std.,it has temperatures reaching as low as -200°C such as those in cryogenics using liquid nitrogen and at this application ST35.8 cannot be used, ST35.8 can be used on CO^2 systems but requires closer examination.
I also suggest you insulate the pipe according to the best standards to prevent moisture ingress.
ASTM A53 or A106 should be fine. I'm attaching an equivalence chart. For low temperature service, I've always preferred ASTM schedule 40 pipe for it's much thicker wall than normal weight DN pipes. This for corrosion allowance. I know, the pipes are supposed to have a good vapour barrier but over the years this invariably gets compromised & ice, freeze/thaw and condensation will deteriorate the pipes.