UNS S32205 duplex stainless steel has been successfully applied in large quantity in the development of high-pressure natural gas fields, including steel pipes, composite steel plates, forgings, etc.
In Chinese oil and gas fields, duplex stainless steel was first used in the KL2 gas field in large-scale, with a single well output at 300×104 m3 / d. The gas field features extremely high pressure, high yield, high temperature, CO2 and high salt content. The KL2 gas field pipeline-gathering network plays a significant role and has the following features: a) the medium to be transported is high-pressure, compressible, combustible natural gas; b) the medium to be transported has strong Cl- and CO2 corrosive tendency; c) the gas field requires high safety and reliability of the pipe network system; d) it requires convenient maintenance and management of the pipe network system; e) it requires materials with good on-site welding performance; f) the project pursues lowest total cost during the entire mining period of the gas field, rather than the minimum one-time input .
Considering these features of the gas field, 2205 duplex stainless steel was selected as the materials for 1) the pipeline-gathering system exposed to the wet natural gas, 2) the seamless steel pipe for the station yard and the treatment plant, and 3) the stainless steel plate for the 120 composite steel plate equipment, for its high mechanical properties, excellent resistance to Cl- and CO2 corrosion and good weldability performance. The composite steel plates of non-standard equipment, the heat exchange tubes and forgings of high-pressure pre-coolers were all made in China.
Due to the special nature of the oil and gas field, like the exceedingly high pressure and corrosion, the supplementary technical requirements were proposed separately along with the basic technical standards.
The supplementary technical requirements are as follows:
- 1) The steel pipe can only have a longitudinal weld with a filler metal. The weld coefficient should be 1.0, and the manufacturer must do whole solid solution annealing treatment to the steel pipe.
- 2) Pitting index PREN is calculated as follows:
PREN = Cr % + 3.3 × Mo % +16 × N % - 3) The ratio of parent metal ferrite needs to fall within 40% to 60%.
- 5) 100% UT and 100% RT inspection on all butt welds of pipe fittings is required. The pipe body of the fitting product should be subjected to 100% surface non-destructive testing;
- 6) The chemical composition must confirm with the requirements of ASTM815 UNSS32205 standard as below, with N % ≥ 0.155 %, PREN ≥ 35 %.
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