Sanitary Valve production nine key steps
Cutting Forming (welding) Heat treatment Surface treatment Cutting Nondestructive testing Surface protection Marking

① Cutting

The materials used for pipe fittings are mainly pipes, plates and bars. The cutting method is selected according to the material properties and the shape of the blank used for the product. The shape, size and other requirements of the blank are carried out according to the process regulations of different products.

For pipes, the commonly used cutting methods are band sawing or bow sawing, gas cutting, and plasma cutting.

For plates, the commonly used cutting methods are gas cutting, plasma cutting, and punching.

For bars, the commonly used cutting methods are band sawing or bow sawing, punching and shearing.

② Forming (welding)

For all pipe fittings manufacturing processes, forming is an indispensable process. Because the forming process of different products is different, the required space is longer and will be described separately in Section 15.2.4. Here, a brief introduction to the heating and welding included in some forming processes is given.

a.. Heating

For the manufacture of pipe fittings by hot forming method, in order to meet the requirements of material deformation in the forming process, the blank needs to be heated during forming. The heating temperature is usually determined according to the material and process requirements.

When hot-pushing elbows or hot-bending pipes are formed, medium-frequency or high-frequency induction heating methods are usually used, and flame heating methods are also used. This heating method is a continuous heating method that is synchronized with the elbow or pipe forming process. The pipe blank is heated during movement and the forming process is completed.

When hot-pressing elbows, hot-pressing tees or forgings are formed, reverberatory furnace heating methods, flame heating methods, induction heating methods or electric furnace heating methods are usually used. This heating is to heat the pipe blank to the required temperature first, and then put it into the mold for pressing or forging.

b. Welding

There are two types of pipe fittings with welds. One is the pipe fittings made of welded pipes. For pipe fitting manufacturers, the forming process of welded pipes is basically the same as that of seamless pipes, and the pipe fitting forming process does not include welding. The other is the welding process required for pipe fitting forming is completed by the pipe fitting manufacturer, such as elbows formed by single-piece pressing and then assembly welding, and tees formed by rolling steel plates into pipe blanks and then pressing.

Commonly used welding methods for pipe fittings include manual arc welding, gas shielded welding, and automatic welding.

The manufacturer should prepare welding process specifications to guide welding work, and should conduct welding process assessment according to the requirements of relevant specifications to verify the correctness of the welding process specifications and assess the welding ability of welders.

Welders engaged in pipe welding operations should pass the examination of the quality and technical supervision department and obtain the corresponding qualification certificate before they can engage in welding work of relevant steel grades (according to the regulations of some industries, welding pipes used in some industries must obtain the welder examination and welding process assessment stipulated by the industry, such as the welding of marine pipes must obtain the welder examination and welding process assessment of the corresponding classification society).

③ Heat treatment

The heat treatment process is an important part of pipe manufacturing. Through the heat treatment steps of heating, insulation and cooling, the work hardening, residual stress, metal deformation defects, etc. generated during the forming process are eliminated, so that the metal structure and properties of the formed pipes change, restore to the state before deformation processing or improve and enhance their performance.

Commonly used heat treatment equipment is reverberatory furnace, electric furnace, etc.; the usual control method is to connect the thermocouple in the furnace to the control device of the temperature-time automatic recorder through a sensor.

The regulations on heat treatment in different pipe product standards are not the same. Not all deformed pipe fittings need to be heat treated. Generally, for low-carbon steel pipe fittings, when the final forming temperature is not less than 723℃ (recrystallization temperature), heat treatment is not required, because the final organizational state is basically normalized under this temperature condition. Heat treatment should be carried out when the temperature is lower than this temperature or higher than 980℃; pipe fittings made of alloy steel or stainless steel should be heat treated regardless of whether they are cold formed or hot formed.

Routine inspection of heat treatment is generally completed through hardness test.

④ Surface treatment

The surface treatment of pipe fittings is usually carried out by sandblasting, shot blasting, grinding, pickling and other methods to remove rust and scratches on the surface of the product, so that the product has a smooth surface and meets the requirements of subsequent processing and inspection.

For pipe fittings treated by shot blasting, the surface hardness will increase slightly.

⑤ Cutting

Cutting is the process of completing the welding end, structural dimensions, and geometric tolerance processing of pipe fittings. For some pipe fittings, cutting processing also includes the processing of inner and outer diameters. Cutting is mainly done by special machine tools or general machine tools; for oversized pipes, when the existing machine tool capacity cannot meet the processing requirements, other methods can be used to complete the processing, such as the method of grinding after gas cutting for large-diameter elbows.

The appearance and size inspection of pipe fittings are usually carried out after cutting.

⑥ Non-destructive testing

Non-destructive testing is an important process for inspecting materials and defects that may occur during the processing of pipe fittings. Most pipe fittings product standards have stipulated the requirements for non-destructive testing, but the requirements are not consistent. In addition to meeting the product standards and ordering requirements for non-destructive testing, some manufacturers with strict quality control also formulate non-destructive testing requirements based on materials, processing technology and internal quality control regulations to ensure the quality of factory products.

In actual work, the determination of the qualified level of non-destructive testing of pipe fittings should be based on the clear provisions of the ordering requirements or standards. Since the surface of the pipe fittings is basically in the state of original pipes, plates or forgings, for the non-destructive testing (MT, PT) of the surface quality of the pipe fittings, if there is no clear grade requirement, it can be graded as II. However, no matter how the qualified grade is stipulated, defects such as interlayers and cracks whose depth is difficult to determine should be considered unqualified. For the non-destructive testing (RT, UT,) of the internal quality of the pipe fittings, if there is no clear grade requirement, the radiographic testing should be graded as II (such as the testing of welds), and the ultrasonic testing should be graded as I.

In order to prevent the defects that may appear in the product during the heat treatment process, the final non-destructive testing of the pipe fittings should be carried out after the heat treatment.

The non-destructive testing of pipe fittings manufacturers in my country usually uses the JB/T 4730 specification. Personnel engaged in non-destructive testing should obtain the corresponding qualifications in accordance with relevant regulations.

⑦ Surface protection

The surface protection of carbon steel and alloy steel pipe fittings usually adopts the method of painting, and the method of passivation after pickling is adopted for stainless steel (for stainless steel pipe fittings with all surface cutting, passivation treatment is not required). The main purpose of the surface protection of pipe fittings is corrosion prevention, and it also achieves the effect of beautiful appearance of the product. Usually, the ordering party makes specific requirements for surface protection, and the manufacturer completes the surface protection of the pipe fittings according to the ordering party's requirements.

⑧ Marking

The marking is an indispensable part of the product and is the basis for achieving traceability requirements. Usually, the product standards stipulate the content and method of marking. The marking content of pipe fittings generally includes the manufacturer's trademark or name, material grade, specification and other content required by the order. The marking methods include permanent marking, such as steel stamping, engraving, electro-etching, etc.; non-permanent marking, such as spray printing, labels, etc.

⑨ Others

In addition to the above-mentioned conventional manufacturing process, 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 the order or material, it should also conduct inspections and tests such as metallographic structure, intergranular corrosion, ferrite, etc. to ensure that the products provided meet the customer's use requirements.