The different standards for flanges mainly involve differences in **system classification** (such as European Standard PN, American Class, Chinese Standard GB, and Ministry of Chemical Industry HG), **pressure rating**, **size marking**, and **applicable industries**.
The following are the core differences between the main standards:
### 1. Internationally Applicable System This is the most fundamental classification in industry, directly determining the compatibility of flanges.
* **European Standard**:
* **Code**: **PN** (Pressure Nominal)
* **Characteristics**: Pressure rating is marked in MPa (e.g., PN16). The larger the pressure rating number, the larger the flange size.
* **Compatibility**: **PN** series flanges can only be paired with flanges of the **same PN series**, and the number of holes, bolt spacing, outer diameter, etc., must be exactly the same. They cannot be interchanged with Class or Chinese Standard flanges.
* **Applications**: Widely used in the petroleum, chemical, and power industries in Asia, Europe, and the Middle East. * **American Standard (ABS):**
* **Code:** Class (Class 150, Class 300, Class 600, etc.)
* **Features:** Pressure rating is indicated in psi (but MPa is commonly used in the Chinese market). Class 150 is equivalent to PN10/PN16.
* **Compatibility:** Class series flanges can only be paired with flanges of the same Class series. They cannot be used interchangeably with PN or national standards.
* **Applications:** North America and some international projects requiring ABS certification.
### 2. Chinese Domestic Standards Domestic standards are mainly divided into **National Standards (GB)** and **Industry Standards (HG/SH)**, which differ significantly in marking methods and scope of application.
* **National Standards (GB):**
* **Full Name:** Such as GB/T 9112 (General Flanges), GB/T 9116 (Socket Welding Flanges), etc. * **Marking Method**: Typically uses the format "DN-Pressure Rating-Sealing Surface", such as `DN125-10A` (indicating a nominal diameter of 125mm, pressure rating of 10MPa, and a flat-faced sealing surface).
* **Characteristics**: The design is relatively conservative, suitable for machinery, construction, and general industrial fields, emphasizing mechanical strength and versatility .
* **Chemical Industry Standard (HG)**:
* **Full Name**: Such as **HG/T 20592** (chemical pipe flange), **HG/T 20615** (large valve flange), etc.
* **Marking Method**: The marking is more complex, including special types of sealing surfaces. For example, `SO300(A)-16` (indicating a ring-welded flange, Class 300, material A, pressure rating 16MPa), or `RF150(A)-4.0` (flat-faced flange, Class 150, material A, pressure rating 4MPa). * **Features**: Designed specifically for the chemical, petroleum, and petrochemical industries, compatible with European (PN) and American (Class) standards. More sealing surface types are available (e.g., RF, RJ, SO, TG, etc.), meeting the zero-leakage requirements for toxic and corrosive media.
### 3. Other Specific Standards
* **Vacuum Flanges**: Such as CF (ConFlat), KF (Klein Flange), etc., typically follow GB/T 6070/6071 standards, used in high vacuum or ultra-high vacuum environments, with sealing methods completely different from ordinary industrial flanges.
* **Ministry of Machinery Standards (JB)**: Such as JB/T 81-94, mainly used for mechanical equipment manufacturing, with marking methods similar to national standards, but material and pressure rating requirements may differ from national standards.
### Key Distinguishing Tips
* **Check "PN" or "Class":** If it's PN16, buy a PN series flange; if it's Class150, buy an American standard flange.
* **Check "GB" or "HG":** GB standard flanges are suitable for general machinery and boilers; HG standard flanges are suitable for chemical equipment handling high pressure, high temperature, or corrosive media.