Main technological process of steel pipe fittings:
> shaping (welding) > heat treatment > surface treatment > cutting processing > non-destructive testing > surface protection > logo
The material used for pipe fittings is mainly pipe, sheet and rod, and the method is selected according to the material characteristics and the shape of the blank of the product. The shape, size and other requirements of the blank are carried out according to the process requirements of different products.
For the pipe, the commonly used feeding method has a sawing machine, cutting, gas cutting, and plasma cutting.
For plank, the commonly used method is gas cutting, plasma cutting, punching and cutting.
For rod, the commonly used method is to cut with sawing machine or bow sawing machine.
Forming is an indispensable process for the manufacturing process of all pipes. Due to different forming process of different products, the length of the required length will be described in section 15.2.4. Here, a brief introduction to the heating and welding of some of the forming processes.
In order to meet the requirement of deformation of material in forming process, heating of billet is needed to meet the requirement of forming process. The heating temperature is usually determined by the material and process.
The method of using medium or high frequency induction heating is usually adopted when the hot bending or hot bending pipe is formed, and the method of flame heating is also adopted. This heating method is continuous heating with the bend or pipe forming process. The tube billet is heated in the movement and completed the forming process.
The method of heating of the reverberatory furnace, the method of flame heating, the method of induction heating, or the method of heating of the furnace are usually used when the hot-pressing bend, the hot pressing tee or forging is formed. This heating is the first to heat the tube to the desired temperature, then put it into the mould to press or forge.
B. the welding
Weld pipe fittings including two cases, one is made of welded pipe fitting, for pipe fittings manufacturer, using the forming process of welded pipe forming process of using seamless tube of basic same, pipe forming process does not include the welding process; Another is done by fitting factory the welded pipe forming need process, such as single chip to suppress again after assembling welding elbow, use steel drum welding into the pipe and then to suppress the tee, etc.
The welding methods of pipe fittings are used in manual arc welding, gas shielded welding and automatic welding.
Manufacturer shall prepare the welding procedure specification to guide the welding work, and should be in accordance with codes for the corresponding welding procedure qualification, to verify the correctness of the welding procedure specification and assess of welding the weld ability.
Welders engaged in pipe welding operations shall be determined by the quality and technical supervision departments of examination and obtain a corresponding qualification certificate shall not engage in relevant steel welding work (according to the regulation of some industries, used for welding pipe fittings to get industry rules in some sectors of welder and welding procedure qualification examination, such as Marine welding pipe fittings to obtain corresponding class welder test and welding procedure qualification).
(3) heat treatment
Heat treatment process is an important part of pipe fitting. By heating, heat preservation and cooling of the heat treatment step, eliminate the forming process of work hardening, residual stress, the metal deformation defects, etc., make the pipe after forming metal organization, performance, change, return to the front of the deformation processing of status, or make it improved and improve performance.
The commonly used heat treatment equipment is the reverberatory furnace, electric furnace and so on; The usual control mode is for the thermocouple in the furnace to connect to the temperature – time recorder control device through the sensor.
There are different rules for heat treatment of different pipe fittings. Not all through the deformation of the pipe fittings are to be heat treatment, usually, for low carbon steel material pipe fitting its final forming temperature is not lower than 723 ℃(recrystallization temperature), can be heat treatment, not because of the temperature under the condition of its ultimate state of organizations is basically normalizing state, or lower than the temperature higher than 980 ℃ heat treatment should be; The pipe fittings of alloy steel or stainless steel shall be heat treated regardless of cold forming or hot forming.
The general test of heat treatment is usually accomplished by hardness test.
Pipe surface treatment usually adopt sand blasting, shot blasting, polishing, pickling, such as method, to remove rust on the surface of the product, such as scratches, make products to achieve smooth surface, to meet the requirements of the subsequent processing and inspection.
The surface hardness of the surface treated with shot blasting is increased slightly.
Cutting machining is the process of finishing the welding end, structure dimension and shape tolerances of pipe fittings. The machining of some pipe pieces is also included in the process of internal and external diameter. The cutting process is mainly done by special machine tool or universal machine tool. When the existing machine tool capacity cannot meet the processing requirements, the processing can be completed in other ways. For example, the method of the burnishing of the large diameter elbow is used.
The appearance and dimension of pipe fittings are usually carried out after machining.
Nondestructive testing is an important process for inspection of defects in the machining process of materials and fittings. The requirements for nondestructive testing are stipulated in most pipe product standards, but the requirements are not consistent. In addition to meet the requirements of product standards and order for nondestructive testing, some of the more stringent quality control of the factory is according to the material, processing technology and quality of internal control regulation on nondestructive testing requirements, in order to guarantee the quality of products.
In the actual work, the determination of the non-destructive testing of the pipe piece shall be specified in accordance with the requirements or criteria of the order. For fitting surface basically is the original state of pipe, plate, or forging, the surface quality of pipe nondestructive testing (MT, PT), if there is no clear requirement according to Ⅱ level grade, but no matter how qualified level regulation, for sandwich and this is not easy to determine the depth of crack defect shall be considered not qualified. Internal quality of pipe nondestructive testing (RT, UT,), radiographic testing if there is no clear grading standards should pressⅡ level (such as weld testing), ultrasonic testing should press Ⅰ level.
In order to prevent the possible defects of the product during heat treatment, the final nondestructive testing of the pipe shall be carried out after heat treatment.
The JB/T 4730 specification is usually used for nondestructive testing of pipe parts in China. Personnel engaged in nondestructive testing shall be entitled to the relevant provisions.
On the surface of carbon steel, alloy steel pipe protection usually adopt the method of painting, after the adoption stainless steel pickling passivation methods (for all surface machining of stainless steel pipe fittings, can need not passivation treatment). The main purpose of surface protection of pipe fittings is anticorrosion, as well as the effect of cosmetic appearance. Normally, the ordering party makes specific requirements on the surface protection, and the manufacturer shall complete the protection of the surface of the fittings according to the requirements of the ordering party.
The hallmark is an integral part of the product, which is the basis for achieving traceability requirements. In general, product standards define the content and method of the logo. The contents of a pipe will generally include the manufacturer’s trademark or name, material grade, specification and other contents of the order. The method of marking includes permanent mark, such as steel seal, engraving, etching, etc. Non-permanent marker, such as print, label, etc.
In addition to the above normal manufacturing processes, the manufacturer shall complete the inspection of raw materials and ensure the correct materials used in order to control the quality of raw materials. In order to meet the special requirements of orders or materials, it should also carry out inspection and testing such as metallographic structure, intercrystalline corrosion, ferrite, etc., to ensure that the supplied products meet the requirements of customers.
Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)