How to inspect flanges? Flange inspection standards and methods

Flange inspection mainly covers appearance inspection, dimension inspection, material identification inspection, quality certificate review and acceptance standard confirmation.

Standard system

Internationally accepted pipe flange standards can be divided into two major systems: one is the European pipe flange system represented by the German DIN standard; the other is the American pipe flange system represented by the American ANSI pipe flange. In addition, Japan's JIS pipe flange standard is also used to a certain extent, but its international influence is relatively limited. Therefore, international flange standards can be specifically divided into:

1. European system pipe flange standards represented by Germany and the former Soviet Union.

2. American pipe flange standards represented by ANSI B16.5 and ANSI B 16.47.

3. The United Kingdom and France each have two independent sets of flange standards.

At the same time, in China, the production and inspection of flanges must also comply with the following national standards and specifications:

• HG/T 20592-2009 Steel Pipe Flanges (PN Series)

• HG/T 20615-2009 Steel Pipe Flanges (Class Series)

Inspection methods

1. Appearance inspection

   • The surface of the cast flange should be smooth and free of forging marks, cracks and other defects. The surface sand and oxide scale must be cleaned up, and any defects that may damage the performance of the casting, such as cracks, shrinkage holes, slag inclusions, etc., are not allowed.

   • The machined surface shall be free from burrs, harmful scratches and other defects that may reduce the structural strength of the flange and the reliability of the connection seal.

   • For the ring-joint flange, the sealing surface must be inspected piece by piece, and the two sides of the sealing groove must not have surface defects such as cracks, scratches, and bumps caused by machining.

2. Material identification inspection

   • The materials selected for steel pipe flanges must comply with the relevant standards.

   • Pipe flanges should generally be made from forgings or castings. Direct fabrication from steel plates is not recommended. Steel plates are only permitted for certain flange types, including flange covers, lined flange covers, plate-type slip-on flanges, butt-weld ring lap joint flanges, and slip-on ring lap joint flanges.

3. Flange dimension inspection

   • All critical dimensions must be strictly checked to ensure they meet tolerance requirements according to the corresponding product specifications or standards.

4. Quality certificate review

   • The quality certification documents provided by the factory must be strictly checked in accordance with the specifications to ensure that key indicators such as chemical composition, mechanical properties, heat treatment status, etc. are consistent with the standard requirements, and the authenticity and correctness of the certificate itself must be verified.