Selection of flange type
Thread Content
I’ve recently reviewed several sets of drawings from design institutes, and for the equipment connection flanges, either necked slip-on flanges or necked butt-weld flanges are used. In my opinion, plate-type slip-on flanges are more than sufficient to meet the requirements; using necked flanges is rather wasteful； I’m wondering whether this approach adopted by design institutes is meant to align with international standards? But it really isn’t necessary, there might be other reasons as well; please give me your advice! Thank you!
Plate butt welding is commonly used for atmospheric pressure vessels and Class 1 vessels, as the pressure is not high and the calculations show it to be sufficient
For large joints, using plate fusion welding results in relatively large welding deformation; necked fusion welding is a more reliable option. For small joints, plate fusion welding is still preferred to save costs.
Design institutes mainly consider safety aspects; they focus on the medium as well as on pressure. Considering these two aspects, plate butt welding cannot be used in many cases, as well as due to the requirements of the overall process piping.
The design of large-scale devices often uses SO or WN. Sealing surface in MFM or TG format. PL+RF is rarely used
I agree with the opinion from the 4th floor; it’s mainly a matter of safety considerations. In some cases, plate-type butt weld flanges are completely sufficient, but for safety reasons, it’s better to use necked weld flanges or necked butt weld flanges. I used to have the same doubts as well. Actually, SO is more commonly used abroad. . . . There’s nothing at all
The design of large devices often uses SO or WN. It is mainly for safety reasons.
But we also need to consider saving money; cut back on things that are unnecessary.
From a safety perspective and considering the process medium.
Generally, for materials that are highly flammable or toxic, cladding flanges are used to ensure safety
When the pressure is too high, or when the medium is toxic or highly corrosive, it is necessary to use neck welding or butt welding, for safety reasons.
The materials for both types of flanges (SO, WN) are forgings. Using sheet metal for flanges is not as good as using forgings.
Flanges and gaskets are selected based on the properties of the medium, taking safety into consideration
I think flat flanges need to be further processed to ensure reliable sealing; otherwise, flanges with a neck are more reliable.
PL flanges are generally not used for flammable and explosive media; if the pressure is not high, SO+RF is chosen instead
It should be determined based on the pressure rating!
I don’t know what your medium is; if it is extremely or highly hazardous, plate flat welding flanges cannot be used.
When selecting flanges, factors such as pressure rating, temperature, and material need to be taken into account. Generally, design firms choose flat-welded flanges for low-pressure applications of 150 lbs (primarily used in circulating water systems); for 300 lbs, welded neck flanges are used, with the sealing surface can be convex. For pressures above 600 lbs, welded neck flanges are definitely chosen, and the sealing surface options include convex-concave and serrated surfaces. For process gases, welded neck flanges are more commonly used
Various flange types have their applicable ranges, and the same applies to seal face types as well. The selection of flange type and sealing surface requires comprehensive consideration of various process conditions such as temperature, pressure, and the type of medium
The sealing issue is a primary concern; since the SO,WN type has higher stiffness, it is necessary to ensure good sealing performance.