Flange inspection refers to the systematic technical evaluation of flanges, mainly focusing on testing their dimensional accuracy, material mechanical properties, surface quality, and sealing performance. Key inspection items include dimensional deviations of outer diameter, inner diameter, and thickness, as well as tensile strength, hardness, surface flatness, and finish. In addition, non-destructive testing can be used to detect surface cracks.
A flange, also known as a flange plate or rim, is a component used in pipeline systems to connect parts such as pipes and valves. It is commonly found in water supply, drainage, energy transmission, and industrial pipeline systems. Its materials include cast iron, carbon steel, stainless steel, and plastics (such as PVC and PP). Plastic flanges are mostly used in corrosion-resistant environments, while metal materials are suitable for high-temperature and high-pressure working conditions.
This component fastens two flanges together through bolt holes with bolts, and achieves pipeline connection by combining gaskets such as asbestos-rubber and metal wound gaskets. It can withstand a pressure range of 0.6 Mpa to 10.0 Mpa. Connection methods are divided into threaded connection, welding (socket welding and butt welding), and loose flange connection. Among them, butt-welded flanges are mostly used in high-pressure systems, and loose flanges are convenient for disassembly and maintenance. According to standards, flanges are classified into chemical industry (HG), petrochemical industry (SH), machinery (JB), and national standard (GB) categories, with nominal diameters ranging from DN10 to DN3000. Forged flanges are often used in high-pressure environments due to process advantages, while cast flanges are suitable for conventional working conditions.
According to material classification, common types include cast iron/carbon steel flanges, stainless steel flanges, PVC/PPR flanges, etc. According to connection methods, they can be roughly divided into threaded (screwed) flanges and welded flanges. Welded flanges can be further divided into socket-welded flanges, butt-welded flanges, blind flanges, and other varieties. According to pressure resistance levels, common ones are 0.6 Mpa, 1.0 Mpa, 1.6 Mpa, 2.5 Mpa, 4.0 Mpa, 6.4 Mpa, 10.0 Mpa, etc.
As for flanges, although most people are unfamiliar with this concept, in fact, every urban resident cannot live without them. Because flanges are widely used for connecting various high, medium, and low-pressure pipelines. For example, urban tap water supply pipe networks, sewage drainage pipe networks, winter boiler heating circulation pipelines, oil and natural gas energy pipelines, etc., all rely on flanges. Their role in pipelines is similar to the connection part between rails on railways, which we are familiar with.
From small to large, common specifications are in sequence: DN 10, DN15, DN20, DN32, DN40, DN50, DN65, DN80, DN100, DN125, DN150, DN 175, DN200, DN225, DN250, DN300, DN350, DN400, DN450, DN500, DN600, DN700, DN800, DN900, DN1000, DN1200, DN1400, DN1600, DN1800, DN2000, DN2200, DN2400, DN2600, DN2800, DN3000, etc.
According to manufacturing materials, flanges can be divided into: WCB (carbon steel), LCB (low-temperature carbon steel), LC3 (3.5% nickel steel), WC5 (1.25% chromium 0.5% molybdenum steel), WC9 (2.25% chromium steel), C5 (5% chromium molybdenum steel), C12 (9% chromium 1% molybdenum steel), CA6NM (4 (12% chromium steel)), CA15 (4) (12% chromium steel), CF8M (316 stainless steel), CF8C (347 stainless steel), CF8 (304 stainless steel), CF3 (304L stainless steel), CF3M (316L stainless steel), CN7M (alloy steel), M35-1 (Monel), N7M (Hastelloy B), CW6M (Hastelloy C), CY40 (Inconel).
