HFW welded steel pipe is always accompanied with the competition and continue to develop a seamless steel pipe. Seamless steel tubes welded steel pipe in order to gradually replace the key is to have high product quality and lower production costs. In order to play HFW pipe wall thickness, geometry regular and low production cost advantages, but also to overcome the mechanical properties of the weld due to inconsistencies arising from corrosion problems and grooves into the traditional high-grade seamless occupied oil and gas pipelines and OCTG and other fields. Recently there has been the idea of seamless pipe.
Seamless is the application of heat treatment process, so that the weld heat affected zone (HAZ) of the microstructure and mechanical properties of the base material tends to be consistent. Currently used mainly three kinds of ways seamless pipe processing: one weld line heat treatment; the second is the overall heating pipe tension-reducing rolling; three is the overall heat pipe.
A weld heat treatment line
1) weld line simulation normalizing (N) heat
Using induction heating weld rapidly heated to austenitizing temperature, usually AC3 reheating temperature 30-50 ℃, but not less than 1010 ℃, making the weld fully converted into austenite martensite, welding slit air cooling to below 700 ℃, to avoid re-formation of martensite, when air cooling to below 370 ℃, cooled with water. The main equipment for induction heating equipment. Select the frequency according to the wall thickness of the pipe, usually 1-3kHZ.
2) weld line quenching and tempering (Q + T) heat
After the weld is heated to a normalizing temperature, water quenching, very fine martensite structure can be formed, and then the weld is heated to tempering temperature, generally 540-700 ℃, air cooled, complete quenching Press Fire (Q + T) heat treatment process. The main equipment for the two sets of induction heating equipment, water spray equipment, production lines longer, larger investments.
2, tension reducing heat rolling
Hot stretch reducing process is actually carried out on the pipe normalizing + thermomechanical treatment. After the base material as a whole is heated to 920-950 ℃, the weld and pipe fully austenitic microstructure, and then reducing mill by tension, rolling sorties large deformation, usually finishing temperature is not low at 850 ℃, to meet the end of the pipe rolling, formed inside the fine uniform grain structure. After a phase transition weld simultaneously with another base metal thermomechanical treatment, and complete the recrystallization process under the same conditions, the microstructure and grain state is bound to converge with the base material, while completely eliminating the pipe forming the internal stress caused. This process is now being taken seriously, is gradually promote the use, for the production of advanced HFW pipe.
3, the overall heat pipe
The whole pipe is heated to normalizing temperature, after all organizations fully austenitic, then cooled. This will basically eliminate the differences between the microstructure of the weld pipe and pipe due to the complete elimination of internal stress generated by forming and welding, but the grain state weld and pipe there are still differences, will bring mechanics inadequate performance and corrosion resistance aspects. The process to use more off-line mode, the use of protective gas to the overall heat pipe heat treatment furnace, another air cooling will take a long time, so production efficiency is low.
Three kinds of seamless technology, currently HFW pipe seamless multi-use online weld heat treatment technology, but comprehensive in terms of the overall heating pipe reducing tension would be an ideal seamless pipe technology, while the overall heat pipe technology Few applications.
Post time: Sep-25-2019