SO neck flat welded flange (Slip-On Hubbed Flange) is a reinforced design of flat welded flange (SO flange). It is characterized by adding a short neck (Hubbed) to the inner hole of the flange and the welding part of the pipe. It is welded to the pipe through the neck, which has the advantages of easy installation of flat welded flange and high strength of butt-welded flange.
Core function: used for connection of pipelines, valves or equipment, suitable for medium and high pressure working conditions (such as PN16~PN40/Class 150~Class 300), it has stronger pressure bearing capacity than ordinary flat welding flanges, and at the same time reduces welding stress concentration.
Typical applications: petrochemical, electrical, pharmaceutical and other systems that require high sealing and strength.
Model and standard
Common criteria:
National standard (GB/T 9116): with neck flat solder flange (SO series, such as PN16, PN25).
American Standard (ANSI B16.5): Class 150, Class 300 with neck flat welding flange.
European Standard (EN 1092-1): Type 01 (with neck flat welding flange).
Model example:
SO-Hub PN40 DN200: represents the national standard flat-welded flange with neck, nominal pressure PN40, diameter DN200.
Core features
Structural optimization
Neck reinforcement design: Add a short neck (Hubbed) to the welded flange and pipe, improving resistance to bending and deformation, and is suitable for pipes with large vibration or temperature fluctuations.
High welding strength: Single-sided corner welds (external welding) are used on the neck and pipeline to reduce the heat-affected zone of welding and reduce leakage risk.
Improved pressure bearing capacity
Compared with ordinary flat-welded flanges (SO), the neck design can withstand higher pressures (PN16~PN40), which is close to butt-welded flanges (WN) performance, but has lower cost.
Easy to install
The installation advantages of retaining flat welded flanges: The pipe is welded directly after being inserted into the flanges, without the need for bevel processing, saving labor time.
Reliable seal
The sealing surface has various forms: protruding surface (RF), concave and convex surface (MFM), tongue and groove surface (TG), and is suitable for high-precision sealing materials such as metal winding pads and graphite pads.
Variety of materials
Common materials: carbon steel (Q235, 20#), stainless steel (304/316L), alloy steel (16Mn, Cr5Mo).
For special working conditions, double-phase steel, Hastelloy and other corrosion-resistant materials can be selected.
Technical parameters
Project Parameter Description
Nominal diameter DN15~DN600 (can be customized to DN2000)
Nominal pressure PN16~PN40 / Class150~Class300
Applicable temperature -29℃ ~ +450℃ (stainless steel material can reach 600℃)
Sealing surface Protruding surface (RF), concave and convex surface (MFM), full plane (FF)
Connection standards GB, ANSI, EN, JIS, DIN, etc.
Application areas
Oil and natural gas: oil pipelines, LNG low-temperature systems.
Chemical equipment: Inlet and outlet of reactor, high-pressure corrosive medium pipeline.
Power industry: high-temperature steam pipelines, boiler water supply systems.
Pharmaceutical food: Clean grade stainless steel neck flange (mirror polished, EP treatment).
Selection and installation suggestions
Key points for selection:
It is preferred for working conditions with pressure above PN16 or temperature >200℃.
Corrosive media are designed with stainless steel (316L) or corrosive anti-corrosion layer.
Installation specifications:
Before welding, the contact surface between the pipe and the flange must be cleaned to ensure that there is no oil stain or rust.
Symmetrical segmented welding is used to avoid deformation caused by local overheating.
After welding, radiation flaw detection (RT) or permeation detection (PT) is required to ensure that the weld is defect-free.
Maintenance requirements:
Regularly check the flange sealing surface and bolt preloading force to prevent leakage due to thermal expansion and contraction.
When discontinued for a long time, anti-corrosion coating is required for the flange neck and welds.
