New martensitic stainless steel for HFW steel pipe

Oil and gas pipeline developed into mid later period, the content of CO2 increased significantly, martensitic stainless steel for oil well pipe can be used in the environment. However, due to the poor weledability of martensitic stainless steel, it was not used widely. In recent years, some new stainless steel improve its welding and are put into use, but there is still no martensite stainless steel used in HFW steel pipe.A good weldability and moisture resistance CO2 corrosion of stainless steel of HFW steel pipe is under development. 

The martensitic stainless steel w (Cr) =11%~13%, and Ni and a small amount of Mo, C and N. Control of chemical composition equips the steel with good corrosion resistance and weldability. Welding using inert gas protection, prevent produced in the welding process of Cr in the form of oxide, welding quality is good, the welded pipe has very good appearance and dimension.1, the material design conceptThe service environment of martensitic stainless steel line pipeTable 1: target properties of a new type  martensitic stainless steel alloy

Yield strength/MPa

tensile strength/MPa

corrosion rate of CO2/mm/a

toughness/J

HardnessHV

Welding

��≥550

��≥620

0.1100 1MPa

��≥40

��-20 full size, horizontal

��≤350

No cold crack�(without preheat and post weld heat treatment)

Note: * including the weld and heat affected zone.

2, The basic concept of  new martensitic stainless steel developmentThe basic idea of this design is to equip the martensitic stainless steel line pipe with good weld strength,good resistance and corrosion resistance welding. In order to get the CO2 corrosion resistant performance is good, w (Cr) must be greater than or equal to 11%; low C and N content to reduce the hardness of the weld heat affected zone; adding Ni to prevent δ-ferrite forming and strength lower of weld heat affected zone; adding Mo to improve the anti SSC ability in the H2S wet CO2 environment.