Seamless Pipe For Sour Service
There is a clear boundary between the application of these seamless pipe. This is generally done by reducing the amount of stress applied to the material (including residual stresses) or by only using alloys that are inherently resistant to stress corrosion cracking. In the case of stress...
There is a clear boundary between the application of these seamless pipe. This is generally done by reducing the amount of stress applied to the material (including residual stresses) or by only using alloys that are inherently resistant to stress corrosion cracking.
In the case of stress corrosion cracking (SSC), H2S near the surface of the steel breaks down during the corrosion reaction into iron sulphides (FeS) and atomic hydrogen (H). This little hydrogen atom is so small that it can easily navigate into the iron crystals in the steel. When it finds a voids, welding porosity, slag inclusion, inclusions from dirty steel-making, etc. the hydrogen atom will prefer to stay there (since there is a little more room). When another hydrogen atom comes along, they prefer to hang out together and form hydrogen gas (H2). With enough exposure to H2S and more and more hydrogen atoms entering the steel, the hydrogen gas pressure increases in the voids in the steel until the steel cracks from the inside out (this is called HIC) or the stress on the steel combines with the stress from inside the steel to cause SSC.
The MR0175 spec wants to prevent SSC in downhole environments, storage batteries, desulphurization systems, piping systems, etc. which take the product up to the fence of the refinery. Beyond that, MR0175 doesn’t apply. For the years between 1975 and 2003, many engineers extrapolated the MR0175 concepts and applied them to the refinery situation
Earlier editions of NACE MR0175 referred only to sour service applications, which lead to the common use of “this pipe meets NACE” without much need for further clarification.
Annex A, Clause A.2.1 lists several requirements including the familiar hardness maximums of 22 HRC (248 HV max in weld zones), nickel content at a maximum of 1%, restrictions on the use of free-machining steels, and requiring heat treatments that would not result in high hardness. There are also restrictions on the use of proper welding procedures, surface treatments and cold work.
This workstation is the hot forming process, and increases the pipe diameter by several inches and refines the wall thickness to the specification requirements. The pipe is heated by induction heating, which is considered a “environmentally-friendly process”, which consumes only electricity, and which does so very efficiently. The heating and expansion occurs through-thickness within minutes, and results in a microstructure and mechanical properties that are consistent with a furnace normalizing heat treatment.