ASME B16.5 Slip on Flange

Slip-on flanges are installed on pipes by slipping on the flange bore over the outside diameter of pipe and securing it to the pipe by fillet welds. There is no full penetration weld between the pipe and slip-on flanges, hence the joint cannot be subject to radiography. A slip-on flange can have a single filled weld or double fillet weld. As per para 328.5.2 of ASME B31.3, if slip-on flanges are single welded the weld is required to be made at the hub. Where two welds are required, one fillet weld is made at the hub of the slip-on flange and the second fillet weld is made at the inside diameter of the flange close to the flange face. The position of pipe inside the slip-on flange should be such that the fillet weld can be carried out without damaging the flange face.The size of fillet weld on the inside of flange is equal to the lesser of pipe wall thickness or 6mm.
ASME B31.3 provides three options of weld details for double-welded slip-on flanges. A slip-on flange shall be double-welded as shown in Fig. 328.5.2B of ASME B31.3 when the service is

• subject to severe erosion, crevice corrosion, or cyclic loading
• flammable, toxic, or damaging to human tissue
• under severe cyclic conditions
• at temperatures below −101°C (−150°F)

• lower procurement cost
• less skill required for installing due to use of fillet welds instead of full penetration butt weld
• weld end preparation not required on pipe ends
• reduced accuracy in the cut length of pipe

• flange installation requires the use of two fillet welds
• non-destructive examination is required on two welds which makes the installation cost approximately the same as weld neck flange
• slip-on flanges are unsuitable for cyclic loading as mentioned above
• slip-on flanges are not available in sizes 2½ inches and over in class 1500 rating and not available in any size for class 2500 rating
• the strength of a slip-on flange is less than that of a weld neck flange due its design (less reinforcement in the hub) and installation method (fillet weld instead of butt-weld)