Because the offshore oil platform riser has long suffered the wave scour, it is necessary to have high strength and excellent resistance to point corrosion material. In all kinds of alternative materials, because super duplex stainless steel possesses austenite and ferrite structure at the same time, it has many advantages such as high corrosion resistance, good mechanical properties and good corrosion resistance to chlorine ion, so it is an ideal offshore platform material.
However, the super duplex stainless steel is sensitive to the third phase precipitation of intermetallic compounds. How to control the production process in the welding and heat treatment process is a difficult point.
First talk about perfect super duplex stainless steel welded pipe manufacturing process, the order including the inspection of raw materials, stainless steel plate, ultrasonic flaw detection, edge planing, shaping, welding, the whole round, cutting, welding, sizing and heat treatment, weld seam detection, pipe end penetrant inspection and hydraulic test, pickling and passivation and finished products after the detection of marker packing.
The next is formed, in the production of welded pipe, the production difficulty is on stainless steel strip edge bending moment applied to ensure effective, more difficult to solve using traditional molding technology; but the yield strength of duplex stainless steel is about two times the ordinary austenitic stainless steel molding, it is also more difficult.
The use of flexible forming technology stick tension effect when bending, the maximum bending moment applied to the edge of the stainless steel belt; favorable conditions and also the use of electrodeless roll used, according to the strength and thickness of the stainless steel belt, adjustable bending forming degree so as to achieve the optimal welding conditions.
The third step is welding, using plasma arc welding and tungsten arc argon arc welding complex welding process. First, plasma arc welding is used to do penetration fusion, so that it has the effect of one-sided welding and double-sided molding. Then TIG welding is used to make filler and cover surface, and pure argon protection is used for welding. In order to reduce the Precipitation Tendency of harmful phase, low line energy is used as far as possible in welding process, and the line energy is better than 16kJ/cm. In addition, the interlayer temperature is very important for the welding of duplex stainless steel. It must be controlled below 100 degrees. The high interlayer temperature will increase the tendency of harmful phase precipitation and ultimately affect the performance of products.
The last is heat treatment. After heat treatment, the whole welding pipe is treated by induction furnace. The heat treatment temperature reaches 1050-1120 degrees, and then water spray is cooled to 40 degrees below.
Source: China Super Duplex Stainless Steel Welded Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)