Why are the pipe flanges on containers always designed as WN type, and why are pipe fittings with imperial wall thicknesses expressed as decimals used?
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I would like to ask the experts here: why are the pipe flanges on containers always designed as WN type, and why are pipe fittings with imperial wall thicknesses expressed as decimals used? We work with equipment, and it’s very difficult to find pipes with decimal precision in terms of thickness or in imperial units; such pipes have to be manufactured by machining cast pipes. WN-type pipe flanges are also made from cast materials, and we are unable to produce them ourselves – we have to outsource this work. The price is too high. It’s really hard to understand why this type is also chosen when the design pressure is very low (0.1–1.6 MPa). Why can’t these flanges be changed to PL or SO type? Under the condition of maintaining the allowable operating pressure, this could help our manufacturing units reduce costs significantly. But the design institute just refuses to meet our requests; I don’t know why. Could someone experienced from the design institute help explain this? Thank you!
In applications where there is a risk of fire and explosion, as well as in situations involving high or extreme hazards, it is not recommended to use PL and SO type flanges; instead, WN type or integral flanges (IF) should be chosen. Check what the medium is.
There are requirements specified in the code, so WN flanges are commonly used; however, for some low-pressure applications, SO flanges can be used as well. But due to convention or higher performance requirements (WN flanges offer better performance than PL and SO flanges), WN flanges are usually preferred. You can discuss this with the client – it’s not necessary to use WN flanges for low-pressure applications; SO flanges are an option.
It’s not necessary to use the WN format; if the user insists on using it, that’s fine as well, but it comes down to cost – if they’re willing to pay, they can do whatever they want. But in most cases, American standard flanges use SO or WN types, while in China, the PL type is mostly used. Regarding the wall thickness issue you mentioned, it’s simply based on imperial units, which is why there are decimals involved; you can also just buy pipes in imperial units! 8\" SCH40. It can also be purchased directly, which makes things more convenient! !
Are you sure you’re using \"cast\" flanges for the connections on the pressure vessel equipment? Under normal circumstances, castings are not allowed to be used in pressure vessel equipment. Pipe flanges under 24" generally use standard ANSI flanges, ASME B16.47, with forgings being the preferred material. As far as I know, the price of standard ANSI flanges isn’t too high, and the connections can be welded by the equipment manufacturer using steel plates, or with standard schedule tubes welded to the flanges.
All these flanges and nozzles are standard items that should be easily available on the market. Our company used to produce few devices that met US standards as well; we were not familiar with all the aspects involved at first, so procurement could not keep up. Things improved once we started producing more of such devices