Types of Tempering of ASTM A53 Line Pipe

The ASTM A53 line pipe is a line pipe that belongs to the American petroleum standard. The line pipe transports the oil, gas, and water extracted from the ground through the line pipe to the oil and natural gas industrial enterprises. Line pipes include seamless pipes and welded steel pipes. The pipe ends have flat ends, threaded ends and socket ends; the connection methods are end welding, coupling connection, socket connection, etc.

API SPEC 5L-2011 (line pipe specification), compiled and issued by the American Petroleum Institute, is commonly used all over the world. The main materials of line pipes are steel grades such as L245, L290, L360, L415, L480, GR.B, X42, X46, X56, X65, X70, X80, X100. Line pipe specification: 10.3-2032×1.7-39.7mm.

With the development of pipeline steel plate technology and the advancement of welded pipe forming and welding technology, the application range of pipeline welded pipe is gradually expanding. Especially in the range of large-diameter group spacing, the advantage of welded pipe is more clear and wet. In addition to the cost factor, welded pipe has Occupying a leading position in the field of line pipes has restricted the development of stainless steel seamless line pipes. In 2004, the output of seamless line pipes was about 400,000 tons, the steel grades included X42-70, and there were onshore line pipes and subsea line pipes.

The production of high-grade steel-grade line pipes currently uses a microalloying heating treatment process. The production cost of stainless steel seamless pipes is significantly higher than that of welded pipes, and with the improvement of steel grades, such as the limit of carbon equivalent for steel-grade line pipes above X80, The conventional technology of seamless steel pipes is difficult to meet user requirements; at present, all 12Cr1moV alloy pipe manufacturers are carrying out scientific research to improve the corrosion resistance of their line pipes and the stable performance in low temperature and high temperature environments.

According to the different performance requirements of GB/T9711.1 pipeline steel pipe, and according to the different tempering temperature, tempering can be divided into the following types:
1. Low temperature tempering (150-250 degrees)
The structure obtained by low temperature tempering is tempered martensite. Its purpose is to reduce the internal stress and brittleness of quenched steel under the premise of maintaining high hardness and high wear resistance, so as to avoid cracking or premature damage during use. It is mainly used for various high-carbon cutting tools, measuring tools, GB/T9711.1 pipeline steel pipes, rolling bearings and carburized parts, etc. The hardness after tempering is generally HRC58-64.

2. Medium temperature tempering (250-500 degrees)
The structure obtained by tempering at medium temperature is tempered troostite. Its purpose is to obtain high yield strength, elastic limit and high toughness. Therefore, it is mainly used for the treatment of various GB/T9711.1 pipeline steel pipes and hot work molds, and the hardness after tempering is generally HRC35-50.

3. High temperature tempering (500-650 degrees)
The structure obtained by high temperature tempering is tempered sorbite. Traditionally, the heat treatment combining quenching and high temperature tempering is called quenching and tempering treatment, and its purpose is to obtain comprehensive mechanical properties with good strength, hardness, plasticity and toughness. Therefore, it is widely used in important structural parts such as connecting rods, bolts, gears and shafts in automobiles, GB/T9711.1 pipeline steel pipes, and machine tools. The hardness after tempering is generally HB200-330.