How To Decide A Flange: Slip On or Weld Neck

1. The application which requires a flange.

Recently a Saudi Arabian client asked for advice on the selection of slip on flange and weld neck flange. In his case, the flange will be applied to a crude oil pipeline in which the working pressure is 10.0 MPa at ambient temperature(21°C ~ 25°C).The flange is designed to connect an ASTM A106 Gr.B 16" SCH100 seamless pipe to a RTJ connection trunnion mounted ball valve(600LB). The client wants us to help him to decide whether a slip on or weld neck flange should be chosen.

2. How to decide to use a slip on or weld neck flange?

As a rule of thumb, slip on flanges are mainly used in utility service such as water supply, irrigation and residential drainage piping, etc. They should never be used in either high pressure, high temperature, nor corrosive services. In this case, although the temperature is not high, crude oil is a hydrogen carrying fluid which is corrosive while the 10.0 MPa and the wall thickness SCH 100 suggest that this is a high pressure service. It is obvious that we must choose a weld neck flange with RTJ face which has a drastically longer fatigue life. The full penetration weld can be achieved by using a WN flange. Besides, on site radiographic(X-ray) inspection on the weld can be conducted easily.

The final choice is: Weld Neck Flange, 600LB ASME B16.5, 16" RTJ SCH100, ASTM A105 material.

Views: Author：hbmetals Date:15/11/18