In the past 30 years, my country’s stainless steel pipes have achieved rapid development and have been widely used in energy industries such as oil and gas drilling, petrochemical, and thermal nuclear power plants, as well as manufacturing and construction industries. The process technology, equipment, variety, quality, market demand, etc. of stainless steel pipes have developed by leaps and bounds, and different stainless steel pipe production technologies and process equipment have been formed. The following is a brief review of the development of stainless steel pipe process technology and equipment.
Development of process technology and equipment
Current status and development of seamless pipe technology and equipment
Since the 1980s, the implementation of the country’s reform and opening up policy has promoted rapid economic development and led to the progress of the seamless steel pipe industry. The production of seamless stainless steel pipes has also grown rapidly, and advanced technology and equipment have been introduced. For example, Jiuli first introduced a 3,500t extruder, which has not only enabled Jiuli’s industrial stainless steel seamless pipe production technology and equipment to enter the world. First, and as a pathfinder of extrusion production technology, it promoted the transformation of my country’s stainless steel seamless pipe technology, and it was listed as one of the 10 major events in China’s stainless steel industry that year. For some important-purpose stainless steel pipes, such as nuclear power plant pipes (special specifications), users mostly use extrusion technology to produce and supply materials, and the production of high-end stainless steel pipes is gradually normalizing; cold-rolled and cold-drawn pipe production equipment is introduced or The localization is even more numerous. The introduction and commissioning of these seamless pipe units has brought my country’s seamless stainless steel pipe technology and equipment to the contemporary international level.
At present, the application field of stainless steel pipes in my country is “cold-rolled and cold-drawn instead of hot-rolled” products. The stainless pipes produced by hot-rolled pipe mills mainly provide pipe blanks for cold processing.
In terms of process technology, most of the seamless steel pipe production lines with advanced equipment in my country were built after 1990. Advanced technologies such as computer control of the production process, tapered piercing machine, full hydraulic roll reduction technology, centralized variable roll design, single roll transmission, limited mandrel rolling, and step mandrel rolling have been widely used. With the continuous advancement of technology and equipment in the seamless steel pipe industry in my country, the production methods of stainless steel pipes (including large diameters and thick walls) have also shown diversified development, mainly including extrusion units, periodic pipe rolling units, pipe jacking units, and Various production methods such as rolling (piercing + cold rolling, cold drawing), hot rolling + cold rolling, and cold drawing. In addition, a small amount is produced by other methods, such as forging and boring.
Hot extrusion process
The hot extrusion process is one of the production processes of hot-processed seamless stainless steel pipes abroad. Compared with the rolling production method, the feature of the extrusion method is that the metal is subjected to three-way compressive stress during the deformation process. In this optimal state, the high-end stainless steel pipe with large deformation resistance and poor thermoplasticity can obtain better internal and external Surface quality and metallographic structure are suitable for the production of small batches and multi-specification stainless steel pipes, especially suitable for the production of high-alloy pipes that are difficult to process by cross-rolling piercing machines.
Although the production of stainless steel pipes in my country adopts the process of “piercing + cold drawing, cold rolling”, the advantage of using the extrusion method to produce stainless steel pipes is that the continuous casting billet can be used directly as the raw material, the product quality is relatively stable, and the variety of replacement is flexible. Directly produce hot-extruded finished pipes, and can also produce various special-shaped section stainless steel pipes. The production of large-diameter (thick-wall) stainless steel pipes basically adopts the hot extrusion process, except for a small amount of “piercing + Pilger rolling” process (including the pipe jacking unit).
With the application of high-speed, automation, and large-tonnage extrusion presses, and the development of high-strength, high-toughness hot-working molds and other related technologies, the use of extrusion methods to produce stainless steel pipes or provide waste pipes for cold processing is the current hot-processed stainless steel pipe A better and economical method. In particular, the production of difficult-to-deform stainless steel pipes, high-alloy steel pipes, and thick-walled pipes has developed rapidly. Figure 1 is the main process flow of a company’s stainless steel extrusion pipe production.
Hot rolling process
In China, stainless steel tube billets are often pierced by cross-rolling. Not only the commonly used austenitic stainless steel, but also the difficult-to-deform duplex stainless steel can also be produced on the cross-rolling piercing machine, which passes through various pipe rolling mills (longitudinal rolling or cross rolling). The tube wall can be rolled thinner. When providing raw materials for cold rolling and cold drawing, the number of cold drawing (rolling) passes can be reduced, which can increase productivity and yield, reduce costs and increase benefits.
The more common devices include Ф50, Ф90, Ф250 series hot rolling piercing units. Another TZC200 tapered roller piercing unit adopts a combined frame, tapered roller piercing, full hydraulic quick roll change and digital display numerical control feeding angle adjustment technology, which is at the leading level and has reached the contemporary international level. It is in some large domestic stainless steel Plants have applications.
Cold rolling and cold drawing process
In the pipe forming process, cold drawing and cold rolling have the same effect in actual production, and the seamless pipes produced have their own advantages. At present, among the stainless steel pipe manufacturing equipment in my country, the series of high-precision cold drawing units such as YLB100t, YLB150t, YLB250t, YLB550t are more common and have a good reputation; among the cold rolling pipe units, LG30-H, LG60-H, LG110-H , LG250-H series units are the most widely used models.
More than 65% of stainless steel pipes are manufactured by cold working, and there are basically three cold working processes: cold drawing process, cold rolling process, and cold rolling + cold drawing process. Cold-worked stainless steel pipes mostly use cold-rolled + cold-drawn production processes, with cold-rolled as the main and cold-drawn as a supplement.