FERRITE-AUSTENITE ALLOY AND METHOD OF MANUFACTURING PIPES THEREFROM Russian patent published in 2005 - IPC

FIELD: flexible pipe manufacture.

SUBSTANCE: invention relates to using stainless steel for manufacturing pipes for developing offshore oil and gas fields and claims using ferrite-austenite alloy containing, wt %: carbon up to 0.05, silicon up to 0.8, manganese 0.30-1,5, chromium 28.0-30.0, nickel 5.80-7.40, molybdenum 2.00-2.50, nitrogen 0.30-0.40, copper up to 1.0, tungsten up to 2.0, sulfur up to 0.010, and iron - the rest. 30 to 70% of the alloy is constituted by ferrite and the rest by austenite. Alloy is used for manufacturing flexible cable pipes to be laid on the marine bottom in the course of development of oil and gas fields. Yield point of the alloy on stretching is at least 750-850 MPa and relative elongation at least 25%. Manufacture of seamless pipes is accomplished by extrusion followed by hot rolling and annealing for 3-10 min at 1040-1080°C. Pipes are welded line-on-line and coiled on drum.

EFFECT: decreased weight of cable due to decreased thickness of its walls enabled because of higher strength of steel and higher corrosion resistance thereof.

5 cl, 2 dwg, 8 tbl, 2 ex