Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
(OP)
Hey all,
This is my first post here, long time lurker though.
I'm a project engineer currently working on a process package for handling wet vapour (approx 10 mol% CO2, 2% H2S). My client's product specifications require that nitrogen is not used as weld shield or backing gas for p8 materials, however I have a sub-supplier who has completed fabrication of their component - a heat exchanger - utilizing a manual GTAW weld procedure utilizing nitrogen as a backing gass. As I was not familiar with the effects of nitrogen on weld quality I've done some quick searching through what is publically available on the internet and it seems nitrogen leads to increased hardness & ferrite levels - undesirable for our system's service but ultimately things that we are able to test for easily.
I wish to propose a deviation to our client's specification allowing for acceptance of the product as is, provided additional testing is complete to satisfy that weld composition, ferrite levels, hardness, etc are all within acceptable levels per NACE stanadards; however I know I have only a very limited understanding of the issues at play. I'm hoping someone with more knowledge can confirm whether this is a reasonable proposition or if I should just reject my sub supplier's product & request a rework?
Thanks,
Jon
This is my first post here, long time lurker though.
I'm a project engineer currently working on a process package for handling wet vapour (approx 10 mol% CO2, 2% H2S). My client's product specifications require that nitrogen is not used as weld shield or backing gas for p8 materials, however I have a sub-supplier who has completed fabrication of their component - a heat exchanger - utilizing a manual GTAW weld procedure utilizing nitrogen as a backing gass. As I was not familiar with the effects of nitrogen on weld quality I've done some quick searching through what is publically available on the internet and it seems nitrogen leads to increased hardness & ferrite levels - undesirable for our system's service but ultimately things that we are able to test for easily.
I wish to propose a deviation to our client's specification allowing for acceptance of the product as is, provided additional testing is complete to satisfy that weld composition, ferrite levels, hardness, etc are all within acceptable levels per NACE stanadards; however I know I have only a very limited understanding of the issues at play. I'm hoping someone with more knowledge can confirm whether this is a reasonable proposition or if I should just reject my sub supplier's product & request a rework?
Thanks,
Jon





RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
thread725-19716: Nitrogen as a Backing Gas
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
http://www.aws.org/wj/supplement/WJ_1975_01_s12.pd...
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
@Stanweld, the material in question is 316L, the chloride content of the fluid is <145ppm, operating temperatures are below 75C, pressures below 200 kPag, solution pH is estimated between 5.2 & 5.5, filler material is ER316LSi; if there are any other parameters that may be useful I'll dig them up.
Thanks all!
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
We actually use nitrogen in weld gas to deliberately raise the N level in the welds.
It can suppress all ferrite formation (this could be a problem in heavy sections) and it noticeably improves the pitting resistance.
Look at most modern grades of SS and you will see N levels of 0.25 up to 0.50 in the base alloys. These need N in weld to prevent depletion in the welds.
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Plymouth Tube
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
thanks all,
Jon Pearson
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
Did you see the paper I attached? You can try to forward it your client for consideration.
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?
RE: Use of Nitrogen backing gas with P8 materials in wet H2S handling environment?