Product Overview
Slip-On Flange (SO flange for short) is one of the most widely used flange types in pipeline systems, mainly used for the connection between medium and low pressure pipelines and equipment, valves or pipe fittings. Its characteristic is that the inner hole of the flange is slightly larger than the outer diameter of the pipe. When installed, the pipe is directly inserted into the inner hole of the flange and fixed by welding the inner and outer double-sided corner welds. Flat welded flanges have the advantages of simple structure, low cost and convenient installation, and are suitable for conventional piping systems in non-extreme working conditions.
Model and standard
International common standards:
National Standard (GB/T 9119): According to the pressure level, it is divided into PN6, PN10, PN16, PN25, etc.
American Standard (ANSI B16.5): Class 150, Class 300, etc.
European standard (EN 1092-1): PN series (such as PN6~PN40).
Model example:
SO PN16 DN100: A flat solder flange representing the nominal pressure PN16 and the diameter DN100.
Core features
Economical and practical
The material consumption is low and the processing technology is simple. The cost is only 60% to 70% of the butt-welded flange (WN), which is suitable for small and medium-sized projects with limited budgets.
Easy to install
The pipe does not require bevel processing, and it is directly inserted into the inner hole of the flange for welding. The inner and outer double-sided corner welds can be fixed, which is highly efficient in construction.
Low flow resistance design
The inner diameter of the flange hole is basically the same as the inner diameter of the pipe, and the medium flow resistance is small, which is suitable for low viscosity fluids such as water, air, and oil.
Material diversity
Conventional materials: carbon steel (Q235, 20#), stainless steel (304/316L).
Special materials: low-temperature steel (used below -20℃), aluminum alloy (lightweight requirement).
Reliable seal
The sealing surface forms include protruding surfaces (RF), flat surfaces (FF), concave and convex surfaces (MFM), and are suitable for non-metal gaskets such as rubber pads and polytetrafluoroethylene pads.
Technical parameters
Project Parameter Description
Nominal diameter DN15~DN2000 (supports non-standard customization)
Nominal pressure PN6~PN25 / Class150~Class300
Applicable temperature -20℃ ~ +300℃ (carbon steel)
-196℃ ~ +500℃ (stainless steel)
Sealing surface form: protruding surface (RF), full plane (FF), concave and convex surface (MFM)
Connection standards GB, ANSI, EN, JIS, DIN, etc.
Application areas
Building water supply and drainage: fire pipes, air conditioning hot and cold water systems.
Industrial pipelines: compressed air, low-pressure steam, circulating water systems.
Food and Medicine: Sanitary grade stainless steel flat welded flange (surface electrolytic polishing).
Ship manufacturing: ventilation ducts, low-pressure fuel ducts.
Agricultural irrigation: PVC or galvanized steel pipe flange connection.
Comparison with other flanges
SO:Comparative term flat welding flange (SO)
Structure without neck, direct welding of pipes
Pressure bearing capacity PN6~PN25
Applicable to low pressure, static load, non-corrosive media in scenarios
SO-Hub:Flat-welded flange with neck (SO-Hub)
Structure with short neck, enhances welding zone strength
Pressure bearing capacity PN16~PN40
Applicable to medium pressure and slight vibration environments in scenarios
WN:Butt-welded flange (WN)
Structural long neck butt welding, high strength transition
Pressure bearing capacity PN10~PN160 (first choice for high voltage)
Applicable to high pressure, high temperature, strong vibration and corrosive media in scenarios
Selection and usage suggestions
Selection principles:
Pressure limit: Only for medium and low pressure systems (≤PN25). High pressure scenarios require a neck or butt-welded flange.
Media compatibility: It is recommended to use stainless steel (316L) or plastic-lined flat-welded flanges for strong acid and alkali media.
Temperature range: The long-term use temperature of carbon steel flange is ≤300℃, and the stainless steel flange can be expanded to 500℃.
Installation precautions:
Welding specifications: The inner and outer welds must be uniform and full to avoid leakage caused by incomplete welding or false welding.
Bolt tightening: Tighten evenly in 2 to 3 times in diagonal order to ensure that the gasket is subjected to uniform stress.
Thermal deformation control: Cool naturally after welding to avoid forced cooling to cause deformation of the flange sealing surface.
limitation:
Not applicable to the following scenarios:
Frequent disassembly (welded structure is prone to fatigue).
High-pressure pulse or violent vibration of pipes (prone to weld cracks).
Contains solid particulate medium (may flush the sealed surface).
Maintenance and troubleshooting
Daily maintenance:
Check the bolt pretension regularly to prevent loosening due to thermal expansion and contraction.
Sealing surface cleaning: Remove rust stains and residual gaskets, and keep the contact surface flat.
Common faults:
Leakage: Replace the gasket or re-tighten the bolts evenly.
Cracked welds: Welding needs to be polished and repaired, and replace the flange in severe cases.
