When to use slip on flanges?

What are slip on flanges?

Slip On Flanges are preferred by some contractors, over the Weld-neck, because of the lower initial cost. However, this may be offset by the added cost of the two fillet welds required for proper installation. The strength of the slip-on flange is ample for it’s rating, but its life under fatigue conditions is considered to be only one-third that of the weld-neck flange.

The slip on flange may be attached to the end of a piece of pipe or to one or more ends of a pipe fitting. The slip-on flange is positioned so the inserted end of the pipe or fitting is set back or short of the flange face by the thickness of the pipe wall plus 1/8 of an inch. This allows for a fillet weld inside the SO flange equal to the thickness of the pipe wall without doing any damage to the flange face. The back or outside of the flange is also welded with a fillet weld.

A variation of the Slip On flange also exists. This is the Slip-On Reducing Flange. This is simply a larger (say a 14″) Slip-On flange blank that, instead of the Center (pipe) hole being cut out (or drilled out) for 14″ pipe it is cut out for a 6″ (or some other size) pipe. The SO Reducing flange is basically used for reducing the line size where space limitations will not allow the length of a weld neck flange and reducer combination. The use of the Slip-On Reducing Flange should only be used where the flow direction is from the smaller size into the larger size.

Slip On flanges or SO flanges are commonly lower in price than weld-neck flanges, and to this effect are a popular choice for our customers.

It is welded both inside and out to provide suffcient strength and prevent leakage.

Slip-on flanges are all bored slightly larger than the O.D. of the pipe. They are preferred over welding neck flanges bu many users due to their lower intial cost, but final intallation cost is probably not much less than that of the welding neck flange because of the additional welding involved.

Advantages of slip on flanges:

Low cost installation
Less time needed to spent on ensuring the accuracy of the cut pipe
They are somewhat easier to align
The slip-on flanges have low hub because the pipe slips into the flange before welding
The flange is welded both inside and outside to provide sufficient strength
They prevent leakage

Standards, Dimensions & Weight

Slip-on flange is slipped over the pipe and then fillet welded. Slip-on flanges are easy to use in fabricated applications.

  • ASME/ANSI B16.5 Class 150 SO
  • ASME/ANSI B16.5 Class 300 SO
  • ASME/ANSI B16.5 Class 600 SO
  • ASME/ANSI B16.5 Class 900 SO
  • BS 3293 Class 150 SO
  • BS 3293 Class 300 SO
  • BS 3293 Class 600 SO
  • DIN 86029 PN 10
Details of Slip On flange

A combination of flange and elbow or flange and tee is not possible, because named fittings have not a straight end, that complete slid in the Slip On flange.

20171215144729 94968 - When to use slip on flanges?
1. Slip On flange 2. Filled weld outside 3. Filled weld inside 4. Pipe


Size: 1/2” to 60”, DN 12mm to DN 1500mm .
Pressure class: Class 150 to Class 2,500, PN 2.5 to PN 250
Facing: RF / RTJ

Material of Slip on flange:

Slip on pipe flanges in stock include AWWA slip on pipe flanges, ANSI slip on pipe flanges, Pressure Vessel slip on pipe flanges and slip on pipe flanges that match the OD and drilling of ASME flanges.

Cabon steel: A105, A350 LF2
Stainless steel: A182 F304/F304L/F316/F316L/F321
Alloy steel: F11, F12

Why use the lap joint flange?

1. Lap joing flange can swivel around the stub end and pipe lining. When the piping system is assembe and disassemble frequently,  it is better to use a Lap joint flange. It means the flange can work even the two flanges bolt holes are misalignment .

2. In a corrosive situation,  the flange joints need to be exchange very soon. To a lap joint flange, only the stub end is touch with the pipe and fluid , the backing flange no need to touch it .  It means you could only replace the stub end , no need to replace the backing flange , so the lap joint flange can decrease the cost of the piping systems.

3. The backing flange and the stub end is seperated , so we can use two different materials for the two pieces.  it can work for  more complicated application.  

Source: China Flanges Manufacturer – Yaang Pipe Industry (www.ugsteelmill.com)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

Please notice that you might be interested in the other technical articles we’ve published:

  • What are orifice flanges

  • What is a Blind Flange

  • What are reducing flanges

  • How to get high quality flanges

Related News

العربيةБългарски简体中文繁體中文DanskNederlandsEnglishFrançaisDeutschBahasa IndonesiaItaliano日本語한국어LatinPortuguêsРусскийEspañolதமிழ்ไทยTürkçe