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Weld Neck Flange

Weld Neck Flange

Weld neck flange is a kind of disc part in pipe fitting, it is most common in pipeline engineering. Weld neck flange construction is convenient, high flange strength, good bearing conditions. Weld neck flange suitable for high temperature and high pressure and low temperature process pipeline can be the most widely used flange, weld neck flange is used in pairs.In pipeline engineering, weld neck flange is mainly used for the connection of pipes. Install one flange for each pipes that need to be connected.The low pressure pipe  use a wire flange ,use weld neck flange for over 4KG pressure, two pieces of flange with a sealing point ,and then bolt fastening . Flanges of different pressures have different thicknesses and use different bolts.

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Application

Weld neck flange are  not easy to deform,well sealed, widely used,with the corresponding rigidity and elasticity requirements and a reasonable butt welding thinning transition, large distance between weld joint and joint surface ,the joint surface is deformed from welding temperature.Weld neck flanges are suitable the pipeline with a wide range of temperature and pressure fluctuations ,and  high-temperature,high-pressure and low-temperature pipelines.It is generally used for connecting pipes and valves with PN greater than 2.5mpaand for pipes conveying expensive, flammable and explosive media.

Manufacturing technique

Forging ,casting,cutting,rolling.

Forged flange:the forging process is generally composed of the following processes: selecting high quality billet blanking, heating, forming and cooling after forging.Forging processes include free forging, die forging and membrane forging. In production,different forging methods are chosen according to the quality of forgings and the number of production batches.

Casted flange:the flange shape size is accurate , small processing, low cost, but has  casting defects (the hole ,the crack,the inclusion); poor streamline shape of inner structure of castings (even worse in case of cutting parts).

Forging and custting are the common manufacturing method of flange.Generally speaking, forging flange quality is better, generally through die forging production, crystal structure, high strength, of course the price is more expensive.

Cutted flange:cut out the disc of the inner and outer diameter and thickness of the flange directly on the center plate, and then process the bolt hole and the water line. The flange produced in this way is called a cutting flange, the maximum diameter of this flange plate width limit.

Rolled flange:the process of making a circle by cutting a strip from a medium plate is called coiling. It is often used in the production of large flanges. After the coiling is successful, it is welded, then flattened, and then the waterline and the bolt hole are machined.

Technical requirements

The grade and technical requirements of the weld neck flange shall comply with the  requirements of JB4726-4728.

1   PN  0.25 MP~ 1.0 MPa carbon steel and austenitic stainless steel forgings allowed the use of level Ⅰ forgings.

2  PN  1.6 MPa to 6.3 MPa forgings shall conform to Ⅱ level or above level Ⅱ forgings levels.

3  In one of the following should accord with the requirement of level Ⅲ  forgings level: (1)  PN≥10.0MPa flange forging; (2) PN>4.0MPa chromium molybdenum steel forgings ;  (3) PN>1.6MPa and temperature ≤-20°c  ferritic steel forgings .

 

Welding flange is generally made by forging or  forging-rolling process. When made of steel plates or sections, the following requirements must be met:

1. The weld neck flange shall undergo ultrasonic inspection without delamination defect.

2. The steel shall be cut into strips along the rolling direction of the steel, and welded into a ring by bending, and the steel surface shall form a cylinder of the ring. The steel plate shall not be directly machined into a butt welding flange with neck.

3. Full penetration welding shall be adopted for the butt welding of the ring.

4. The welding  of the ring shall be subjected to post-weld heat treatment and 100% radiation or ultrasonic inspection, and the X-ray inspection shall meet the requirements of grade II of JB4730 and the ultrasonic inspection shall meet the requirements of grade I of JB4730.

The lateral gradient of neck of weld neck  flange shall not be greater than 7o. The technology parameters of weld neck flange are strictly controlled during production and welding to ensure that it can fully play its role and value in production and use.

Material

WCB , LCB,LC3,WC5,WC9,C5,C12,CA6NM,CA15,CF8M,CF8C,CF8,CF3,CF3M,CN7M,M35-1,N7M,CW6M,CY40.

Manufacture standard

 chemical industry standards :HG/T20592-2009、HG/T20615-2009、

national standards:GB/T9115.1-2000、GB/T9115.2-2000、GB/T9115.3-2000、GB/T9115.4-2000、

Mechanical standard :JB/T86.2-94

Marine standard :CB/T47-1999

 

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