High Partial Pressure H2S Pipelines
High Partial Pressure H2S Pipelines
(OP)
We are constructing a pipeline which will operate at around 1000 psig. The gas will contain 1000 ppm to 4000 ppm H2S in natural gas. I have a chart that indicates the line should be constructed to NACE Plus. What is NACE Plus? I have done plant construction to NACE. However, I have not done pipeline construction to the extent of stress relieving welds. Is stress relieving typical for pipelines. Can X-42 pipe conform to NACE MR-0175?





RE: High Partial Pressure H2S Pipelines
SSCC is prevented by reducing the residual stress in the steel; HIC is prevented by altering the steel chemistry (low levels of manganese inclusions, micro alloying additions to control the shape of these manganese inclusions) and by controlling the steel's processing. Talk to a steel mill for more information and advice.
PWHT is often done on pipeline construction, especially offshore where they tend to use higher strength steels and automatic welding machines. Onshore it can be done, but it's a pain...
RE: High Partial Pressure H2S Pipelines
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: High Partial Pressure H2S Pipelines
http://www.standard.no/imaker.exe?id=1369
Best regards
Morten Andersen
RE: High Partial Pressure H2S Pipelines
RE: High Partial Pressure H2S Pipelines
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: High Partial Pressure H2S Pipelines
Table 1 of ISO 15156-2 states that it is applicable to "flow-lines, gathering lines, transportation pipelines for liquids, gases, and multiphase fluids."
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: High Partial Pressure H2S Pipelines
I was working on a Shell pipeline project several years ago and they had a specification for Line Pipe conforming to NACE MR0175 and a separate Sour Service Line Pipe specification. As I remember, the difference between the two was the sour service line pipe had much tighter limits on the steel chemistry and allowable processing (ie achieving strength by controlling the cooling rate was preferred to cold working the steel by rolling it and so on). MnS inclusions are very ductile and can form large'pancake' shaped inclusions in a rolled steel, which then act as nucelation site for atomic hydrogen fromteh H2S to form hydrogen molecules inside the steel matrix, leading to hydrogen blistering, step wise cracking etc.
My guess is that "NACE Plus" isn't an official specification and is proabaly a client specific shorthand for restricting the hardness as per NACE MR 0175 (to pretect against SSCS) and also reducing the amount of Mn & S and adding micro alloying elements to the steel chemistry (to protect against the other H2S failure mechanisms). Changing the steel chemistry radically means you might have to move to Pce rather than CE for your weldability considerations, too.
RE: High Partial Pressure H2S Pipelines
The usual Shell specification for linepipe kills the SSC/HIC birds with the same stone - seems strange to have 2 specs. ISO 3183-3 does a better job than API 5L in this respect too.
Personally, I hope never to have to refer to NACE MR0175 again as, to me, it is ISO 15156. ISO 15156-2 also deals with HIC, SOHIC, SZC, and SWC although it does not give the chemistry restrictions that have become the norm.
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: High Partial Pressure H2S Pipelines
RE: High Partial Pressure H2S Pipelines
My understanding is that ISO 15156-1,2,3 are supposed to be identical to NACE MR0175 and that the latter designation is only maintained because US laws explicitly refer to MR0175. I have not seen a copy of the "equivalent" version of MR0175 but am concerned when people refer to clause numbers in it that do not appear to match with ISO 15156 which suggests that, editorially, they may not be identical.
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: High Partial Pressure H2S Pipelines
Thanks.
Best regards
Morten