E-mail: authentic013@steelpipes-fitting.com
WhatsApp: +86 13668807131
E-mail: authentic013@steelpipes-fitting.com
WhatsApp: +86 13668807131
Jul. 11, 2025
Weld Neck Flange (WN) and Slip-On Flange (SO) are two commonly used flange connection methods in industrial pipeline systems. They have obvious differences in structure, welding method, applicable working conditions and performance characteristics.
1. Structural differences
Weld Neck Flange: With a tapered high neck, the flange and the pipe are butt welded (Butt Weld), and a groove needs to be opened during welding to ensure penetration. The neck design can effectively disperse stress and improve the connection strength.
Slip-On Flange: There is no neck structure. The flange is directly sleeved on the outside of the pipe and welded on both sides of the inside and outside through the fillet weld (Fillet Weld). The installation is simple, but the weld strength is relatively low.
2. Welding method
Weld Neck Flange: Butt welding is adopted, and the weld is of equal strength to the pipe. After welding, non-destructive testing (such as X-ray RT or ultrasonic UT) is required to ensure the welding quality.
Slip-On Flange: Fillet welding is adopted, and no groove is required during welding. The installation speed is fast, but the weld strength is not as good as butt welding. It is suitable for low-pressure and non-critical occasions.
3. Applicable working conditions
Butt welding flange: suitable for high pressure, high temperature, large vibration or stress concentration, such as petrochemical, high temperature steam pipeline, flammable and explosive medium transportation, etc.
Slip welding flange: mainly used for low pressure, normal temperature, no severe vibration working conditions, such as ordinary water treatment, low pressure air or inert gas pipeline, etc.
4. Performance characteristics
Butt welding flange:
High strength, strong weld and pipeline, good fatigue resistance.
Good sealing, suitable for harsh working conditions.
Strong deformation resistance, can withstand large thermal expansion and contraction and mechanical stress.
High installation requirements, precise alignment, high welding and testing costs.
Slip welding flange:
Low cost, less material consumption, quick installation.
Applicable to space-constrained occasions, no need to reserve long neck space.
Weak deformation resistance, long-term vibration or temperature changes may cause weld cracking.
5. Selection recommendations
Preferably use butt-weld flanges for high pressure (PN40/Class 600 or above), high temperature, toxic/flammable media, frequent thermal cycles or high vibration pipeline systems.
Preferably use flat-weld flanges for low pressure (PN16/Class 150 or below), normal temperature, non-critical pipelines or projects with limited budgets.
6. Precautions
The welding quality of butt-weld flanges directly affects safety and must be strictly tested in accordance with standards (such as ASME B31.3).
Flat-weld flanges are not suitable for pipelines with pulsating loads or frequent temperature changes, otherwise they are prone to weld fatigue failure.
In summary, butt-weld flanges are superior in strength and reliability, but the cost is higher; flat-weld flanges are economical, but have a limited scope of application. When choosing, you need to consider pressure, temperature, medium characteristics and cost factors.
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