Process flow of steel pipe fittings manufacturing

- Feb 27, 2019-

I. Tools/raw materials: pipes, plates and rods

II. Steps / Methods

1.The lower feed  
      pipe materials used for the main pipes, plates and bars, according to the method of feeding the material properties and shape of the selected product with the blank. Blank shape, dimensions and other requirements for different products in accordance with a predetermined process. For tubes, there is a method commonly used cutting band saws or bow Saw cutting, gas cutting, plasma cutting. 
      For plates, cutting methods are commonly used gas cutting, plasma cutting, press punching. 
For the bar, there is a method commonly used cutting band saws cutting or sawing machine bow, punching cut.

2. Forming (welding) 
      For the manufacturing process of all pipe fittings, forming is an indispensable process. Because the forming process of different products varies.

A. Heating

      In order to meet the requirement of material deformation in the forming process, the billet needs to be heated during the forming process. Heating temperature is usually determined according to material and process requirements. -

      When forming a hot push elbow or a hot bend pipe, the method of medium or high frequency induction heating is usually used, and the method of flame heating is also used. This heating method is continuous heating synchronously with elbow or elbow forming process. The billet is heated in motion and the forming process is completed.

      When hot-pressing elbows, hot-pressing tees or forgings are formed, the methods of reverberatory furnace heating, flame heating, induction heating or electric furnace heating are usually used. This kind of heating is to first heat the billet to the required temperature, then put it into the die to press or forge.

B. welding

      Pipe fittings with weld include two cases. One is pipe fittings made of welded pipe. For pipe fittings factory, the forming process of welded pipe is basically the same as that of seamless tube forming process. Tube forming process does not include welding procedure, and the other is the welding procedure needed by pipe fitting manufacturer to complete tube forming. The three links are welded into steel billets and then pressed by steel rolls.  

      Pipe fittings are usually welded by manual arc welding, gas shielded arc welding and automatic welding.  

The manufacturer shall compile welding procedure rules to guide welding work, and shall carry out welding procedure qualification according to corresponding specifications, so as to verify the correctness of the welding procedure and assess the welder's welding ability.  

      Welders who are engaged in pipe welding work should pass the examination of the quality and technical supervision department and obtain the corresponding qualification certificates before they can engage in the welding work of the relevant steels. (according to the regulations of some industries, the welds examination and welding qualification assessment for the industries shall be obtained in the welding pipes of some industries, for example, the welds examination and welding technology evaluation of the corresponding classification societies should be made for the welding of ship fittings. Fixed).

3. heat treatment

      Heat treatment process is an important part of pipe manufacturing. Through heat treatment, heat preservation and cooling process, the work hardening, residual stress and metal deformation defects formed during the forming process are eliminated, so that the metal structure and properties of the formed pipe are changed, and the state of the tube is restored to the pre deformation state or the performance is improved and raised.  

      The commonly used heat treatment equipment is reverberatory furnace and electric furnace. The usual control mode is that the thermocouple in the furnace is connected to the control device of the temperature time automatic recorder through the sensor.  

      There are different regulations for heat treatment in different product standards. Not all deformed pipes are subjected to heat treatment. Generally, the final forming temperature of the tubes of low carbon steel is not less than 723 C (recrystallization temperature) without heat treatment, because the final microstructure state is basically normalizing under this temperature condition, and the heat treatment should be carried out below this temperature or above 980 C; alloy steel or stainless steel material. Heat treatment should be carried out whether the tube is cold formed or hot formed. The conventional inspection of heat treatment is usually done by hardness test.

4. Surface treatment

     Surface treatment of pipe fittings is usually carried out by sand blasting, shot blasting, grinding and pickling to remove rust and scratches on the surface of the product, so that the product can reach a smooth surface and meet the requirements of subsequent processing and inspection.  

The surface hardness of the tube treated by shot blasting will increase slightly.  

5. Cutting

      Cutting is a process to complete the welding end, structural dimension, shape and position tolerance of pipe fittings. The cutting of some pipe fittings also includes the processing of inner and outer diameters. Cutting is mainly accomplished by special machine tools or general machine tools. For large-sized pipe fittings, when the existing machine tools can not meet the processing requirements, other methods can also be used to complete the processing, such as gas cutting and grinding method for large-caliber elbows.  

The inspection of appearance and dimension of pipe fittings is usually carried out after cutting.

6. nondestructive testing

      Nondestructive testing is an important procedure for testing defects that may occur in the process of material and pipe fittings. The requirements of NDT for most pipe fittings standards are specified, but the requirements are not consistent. In addition to meeting the requirements of product standards and ordering requirements, non-destructive testing is being carried out in some factories which are relatively strict in quality control. According to the requirements of materials, processing technology and internal quality control, NDT requirements are formulated to ensure the quality of the products manufactured.  

       In actual work, the determination of qualified grade of pipe nondestructive testing should be specified according to the order requirements or standards. As the surface of the pipe is basically the state of the original pipe, plate or forgings, for non-destructive testing (MT, PT) of the surface quality of the pipe parts, if there is no definite grade requirement, it can be classified as grade II, but no matter how the qualification level is specified, the defect that is not easy to judge the depth of the sandwich and crack shall be regarded as unqualified. For non-destructive testing (RT, UT) of pipe internal quality, if there is no clear requirement, the level of radiographic examination should be classified according to grade II (for example, weld seam detection), and ultrasonic testing should be classified as grade I.  

To prevent possible defects in the process of heat treatment, the final NDT of pipes should be carried out after heat treatment.  

7. surface protection

      The surface protection of carbon steel and alloy steel pipe is usually done by painting, passivation of stainless steel after pickling. The main purpose of pipe surface protection is anticorrosion, and at the same time, the appearance of the product is beautiful. Usually, the ordering party makes specific requirements for the surface protection. The manufacturer completes the protection of the pipe surface according to the requirements of the ordering party.

8. mark

      Logo is an integral part of products and a basis for achieving traceability requirements. Usually, the content and method of the logo are stipulated in the product standard. The contents of the pipe mark generally include manufacturer's trademark or name, material grade, specification and other contents of the order. The methods of marking include permanent marks, such as steel engraving, engraving, electrical erosion, and so on. Non permanent marks, such as inkjet printing, labels and so on.

9. points for attention

     In addition to the above conventional manufacturing processes, in order to control the quality of raw materials, the manufacturer should also complete the inspection of raw and auxiliary materials to ensure the correctness of the materials used. In order to meet the special requirements of orders or materials, inspection and testing such as metallographic structure, intergranular corrosion and ferrite should be carried out to ensure that the products provided satisfy the requirements of customers.

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