Water & air lines: Slip-on versus weld neck flanges ? 1

[MBOT]

Greetings all
Our plants currently utilize a line class specification for utility water and air applications that specifies the use of 150# FF slip-on flanges for pipe sizes 2-24".
Given that this is an old line spec (up for review), catering for non-lethal services, i was wondering whether anybody has any experiences which would justify NOT converting from slip-on to weld neck flanges (apart from the cost of ocassionally maching raised faces off)?

 

[bvi]

Slip on flanges are perfectly suitable for the service. If you are using the spec for new or replacement flanges, you should consider changing to raised face flanges if these are steel, not cast iron flanges. The flat face flanges are typically for use with full face gaskets, and for bolting to cast iron flanges (e.g. at pumps). On the other hand, perhaps the spec calls for flat face flanges because it has cast iron valves with flat faces.

 

[saxon]

MBOT, It sounds as if the original piping spec. was set up using the rational of material cost (slip-ons or Weld necks will work in this service). From an item cost, slip-ons are less expensive, but when one considers the "as installed" cost the weld necks are cheaper. The weld neck has only one circumfrential weld that needs to be made, whereas the the slip-on has two. Doubling the welding cost. In the larger sizes, say 10-24" you may want to use slip-ons, in this size range, weld necks can get a bit expensive. You'll need to make a cost analysis to get the best economic break point.

Hope this helps.
saxon