Standard Pipe Flange Selection Principles - Wholesale Supplier of 2/4-inch Pipe Flanges

Pipe flanges, gaskets, and fasteners find extensive use in chemical engineering design. They constitute vital components of piping systems, pipe fittings, valves, and various equipment parts such as manholes, hand holes, liquid-level gauge mirrors, and more. Moreover, they have broad applications in thermal engineering, water supply and drainage, heating and ventilation, and instrumentation. Therefore, how can we ensure their correct selection?

Selection principle 

Hg/t 20592, Hg/t 20606 to 20607, and Hg/t 20611 to 20614 (European system) are commonly recommended standards for selecting pipe flanges, gaskets, and fasteners. Similarly, Hg/t 20615, Hg/t 20623, Hg/t 20627 to 20628, and Hg/t 20630 to 20635 (American system) are preferred options.

The nominal pressure of a standard pipe flange is determined by dividing the pressure carried by the pipe into several standard levels, as specified by the standard's guidelines. Each grade (PN) signifies the maximum allowable working pressure of the flange under specific material and operating temperature conditions. The pipe flange's nominal pressure (PN) is derived from the designated material yield strength of 225MPa to calculate the maximum allowable working pressure (P) at varying operating temperatures. When there are discrepancies in flange material and working temperature, the maximum allowable working pressure may either decrease or increase. The calculation method for determining the maximum allowable working pressure (P) at different operating temperatures is as follows:

p=PN × (design strength /225)

The minimum values considered for design strength are as follows:

• When the working temperature is lower than the material's creep temperature, the material's yield strength is used.

• At the creep temperature, the maximum allowable stress of the material should be multiplied by 1.5.

• If the material's design strength exceeds 225MPa, the value of 225MPa should still be used.

The selection principles for pipe flanges in pressure vessels are as follows:

50. Threaded flanges, plate flat welding flanges, flat welding ring loose flanges, neck flat welding flanges, and lined flange covers are not recommended for use with flammable, explosive, or highly hazardous media.
50. For explosive or moderately toxic media, the nominal pressure of the pipe flange should not be less than 1MPa. For highly toxic and extremely or strongly permeable media, the nominal pressure of the connecting flange should not be less than 16MPa.
50. When the vacuum degree of the vacuum vessel is less than 600mmHg, the nominal pressure of the pipe flange should not be less than 0.6MPa. When the vacuum degree is between 600~700mmHg, the nominal pressure of the pipe flange should not be less than 1MPa.
50. Highly hazardous and extremely hazardous media, as well as Class III pressure vessels, should use neck butt welding flanges.
50. Flange forgings' grade and technical specifications must adhere to the standards' stipulations.
50. Service conditions for standard-grade hexagon bolts: 

PN is less than or equal to 1.6MPa; non-aggressive circulation environments; Equipped with non-metallic gaskets; The medium is non-flammable, non-explosive, and non-toxic.

50. Service conditions for commodity-grade stud bolts and nuts:

PN≤4.0MPa; Non-violent circulation occasions.

50. When using austenitic stainless steel flanges, the following provisions shall be met:

1. Austenitic stainless steel flange fasteners should be made of materials with similar linear expansion coefficients.

2. Ordinary austenitic stainless steel flange fasteners, such as A2-50, are suitable for use with non-metallic flat gaskets, PTFE-coated gaskets, and flexible graphite composite gaskets without undergoing cold work hardening.

3. When the working temperature does not exceed 230°C, ferritic steel (carbon steel or alloy structural steel) fasteners can be utilized.

4. Cold-work-hardened austenitic stainless steel flange fasteners, like A2-70 and A4-70, can be used with semi-metallic gaskets such as spiral wound gaskets, metal clad gaskets, and tooth-shaped composite gaskets, among others.

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