Tee pipe fittings of material selection
Using hot drawing skill produces in the process of tee, the original data of metallographic arrangement, impact strength, patience and weldability of parameters will be the base attack a repeat of the heat change. Selected for this demand information is not as long as excellent high temperature plasticity, easy to deformation processing; Together on the premise of meet the weldability, it is necessary to have good hardenability, to ensure that the tee after proper heat treatment, can make its connected with the main pipe with fundamental equal strong patience and excellent weldability, this is the basic demand for hot drawing tee selection. Excellent weldability, suitable hardenability, high temperature plastic, after hot working with high strong patience is the basic principle of hot drawing tee data selection, reasonable disposal of the several aspects of necessary.
1. The large-diameter molding and high temperature plasticity
Tee pipe fittings production process essence is the high temperature hot working again for data process, data in high temperature conditions should have excellent plasticity, easy to deformation processing; Its formability, besides is conditioned by the mold material of high temperature plastic deformation of tee pipe fittings processing has a great influence, it was to hot tee deformation processing temperature pull the skills of the root, also avoid tee pipe fittings in the process of forming crack controlled according to the shortcomings. Data of high temperature plastic stand or fall reflects this kind of material at high temperature of plastic bump, shorten the section of steel rate one temperature curve is an important physical parameter of paint materials high temperature delay plastic. Containing niobium (Nb) steel in the austenite of low temperature zone and high temperature low temperature zone + ferrite austenite have plastic drop in appearance, the former with niobium compound in austenite in low temperature zone along the austenite grain boundary to separate, the latter with the high low temperature zone + ferrite austenite occur along austenite grain boundary proeutectoid ferrite.
2. Hardenability and low carbon content
Tee from both at home and abroad indicate that natural gas transport pipeline with WPHY70 produce high strength, large diameter tee skill is not very sophisticated, thus complete the X60 tee pipe fittings to WPHY70 tee pipe fittings production skills to break has important practical significance. The strength of the hot drawing tee is done through quenching + back to fiery disposition skills, both the original data after quenching cooling quenching arrangement, the amount of satisfied by fiery disposition, tee intensity reached WPHY70 grade of steel demand. The higher the data hardenability and the higher the strength after quenching, improve the hardenability, it needs to add endowment guess C, Mn, Cr, Ni, Mo, Nb, V and affect the hardenability of alloying elements. But, although the increase of the content of alloy elements, improve the hardenability, but together can make the data of carbon equivalent, weldable function. Therefore, hardenability, appropriate low carbon equivalent is the first question of WPHY70 tee selection. Under the condition of the goods, to satisfied outdoor harsh welding skill requirements, line pipe carbon equivalent control in C.. 0.40 or less, fittings, commodities carbon equivalent control in G. Below 0.44 or less. Far low carbon equivalent of parent metal contained in C, Mn, Cr, Ni, Mo, Nb, V, etc on the hardenability dedication larger alloy element content is very low, small data hardenability coefficient, obviously, in this case, the weak hardenability steel just relying on the progress hardenability high strength is relatively difficult to ensure that the tee. Metallographic arrangement is the main factor resolution steel mechanics performance, metallographic arrange varieties and amount of different, led to the difference between its mechanical performance. Weak hardenability steel can use quenching after many subtle quenching intensity of arrangement for progress. Change of quenching medium, add phase change super-cooling degree, in order to obtain more martensite and bainite is arranged, and then advances the 3-way intensity.
Domestic tee pipe fittings of traditional material thinking is based on the bag yesterday of energy such as electricity, chemical industry pipeline and equipped with the special needs of the warp and woof of above, mostly in alloy steel, heat-resistant steel, high manganese steel and general carbon steel is given priority to, such as power plant main steam control path using tee pipe fitting material for 12 crlnovp22 heat-resisting steel, general pipe tee pipe material selection for the 20, 209, Q345 steel, corrosive environment with 306 l, etc.
The connotation of the traditional material tensile strength, bending strength, patience and other mechanical performance index and weldability and oil and gas pipeline with control steel has bigger distance, three general steel 20, 209, general pipeline Q345 steel not only data such as strong patience is low, its weldability cannot compared with pipeline steel with high strength control, pressure vessel with 14 15 mnmonbg mnmovg, steel, strength can be satisfied with the demand, but a 30. C charpy impact patience can not meet the demand planning parameters. Line with control steel although have high strength, high tolerance and good weldability strengths, but because of its low alloy content, low hardenability and defects, is not suitable for directly chosen for hot drawing tee pipe fittings production data, tee pipe fittings used in domestic natural gas pipeline data needs to be studied.
To sum up, think about C, Mn, Nb, V and alloy element content on the strength of X70 grade three special plate strong patience and weldability, the effect of Nb, V, Mo alloy element content on the influence of carbon equivalent and ambitions hardenability, and the content of micro alloying elements on the influence of molding temperature, choose low carbon alloy steel composition planning road, give full play to the Nb, V and intense form carbide elements separated reinforcement and hallooing grain growth effect, study American standard MSS SP75-1998 rules WPHY series of pipe steel, put forward the “west-east gas pipeline project of X70 tee pipe fittings for steel order skill conditions”.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)