slip on (so)
slip on (so)

Slip-On (SO)

Description

The Slip-On flange is designed to have an internal diameter slightly larger than the outer diameter of the pipe.

  • The Bore: Unlike a Weld Neck flange that matches the pipe’s internal diameter, the SO flange bore is slightly oversized so it can slide onto the pipe like a ring.

  • Low Profile: It typically has a shorter hub than a Weld Neck flange, making it more compact.

  • Welding Method: It requires two fillet welds—one on the outside (at the hub) and one on the inside (at the pipe end).

  • Face Types: Most commonly found with a Raised Face (RF) or Flat Face (FF).

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1. Working Principle

The working principle of a Slip-On flange is based on Double Fillet Welding:

  • Positioning: The pipe is inserted into the flange. Crucially, the pipe end is usually set back from the flange face by a distance equal to the pipe wall thickness plus 3mm. This prevents the weld bead from damaging the flange face.

  • Securing: A welder applies a fillet weld to the back of the flange (where it meets the pipe) and another fillet weld on the inside of the flange near the face.

  • Alignment: Because the flange can slide back and forth before welding, it is much easier to align with bolt holes on mating equipment than a butt-welded flange.

2. Primary Use

The primary use of a Slip-On flange is for Low-Pressure, Non-Critical Applications.

It is preferred over other flanges when:

  • Cost Savings are a priority (the flange itself is cheaper to manufacture than a Weld Neck).

  • Ease of Assembly is needed (less precision is required when cutting the pipe to length).

  • Space is limited (the shorter hub allows for tighter piping configurations).

3. Common Applications

Slip-On flanges are the “standard” for utility and light industrial piping:

Industry Application
Water Works Municipal water lines and low-pressure cooling water systems.
HVAC Chilled water and hot water circulation in commercial buildings.
Pneumatics Low-pressure compressed air lines in factories.
Oil & Gas Secondary “utility” lines (firewater, lubrication oil) where pressure is low.
Food & Beverage Low-pressure transfer lines for non-hazardous ingredients.

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