The underlying logic of flange selection is actually to correctly place the five points of diameter,pressure,temperature,medium and standard in sequence,and the model will naturally be locked.

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First,confirm DN.The nominal diameter is just a size code,which is neither equal to the outer diameter nor the inner diameter of the pipe.Its function is to unify the flange outer circle,the number and aperture of bolt holes,and the sealing surface size.For example,a pipe marked"Φ108×4.5"generally corresponds to DN100;it is more straightforward on equipment drawings,which will clearly state"DN150 nozzle".If the nominal diameter cannot be determined,the subsequent pressure level and sealing form cannot be advanced.

Second,check the pressure level.China uses the PN series(PN6,PN10,PN16...),and the American standard uses the Class series(Class150,300,600...).When selecting the pressure level,you cannot only look at the design pressure marked on the pipe—the operating temperature must be taken into account together.As the temperature rises,the allowable stress of the flange material will decrease.In occasions where PN16 can withstand 1.6MPa originally,it may be necessary to switch to PN25 for safety at high temperatures.When involving flammable,explosive or toxic media,it is recommended to proactively upgrade one pressure level.

Third,consider the temperature condition.Normal temperature working conditions are the most lenient,and carbon steel can handle them;in low temperature environments,carbon steel is prone to brittle fracture,so it is necessary to switch to low temperature carbon steel or stainless steel;once entering the continuous high temperature zone,the strength of carbon steel drops sharply,and only alloy steel or even nickel-based alloy can be used.

Fourth,look at the medium.What fluid is being transported directly determines the flange material and sealing surface form.Non-corrosive water,air and steam are most economical with carbon steel matched with RF raised face;for slightly corrosive seawater and weak acids,304 or 316L stainless steel can be used;for strongly corrosive media,2205 duplex steel and Hastelloy must be used,and the sealing surface should be changed to TG tongue and groove face or RJ ring joint face.In working conditions containing chloride ions,304 stainless steel has a great risk of pitting corrosion,so 316L or duplex steel is preferred.If it meets the cleanliness requirements of the food and pharmaceutical industry,or the pipeline system matched with the rotor pump,the material must also take into account the sanitary standard.

Fifth,align the connection form and standard.For low pressure and normal temperature,plate flat welding flange is cost-effective;for medium pressure and medium temperature,neck flat welding flange is selected,which balances strength and cost performance;for high pressure,high temperature and high-risk media,neck butt welding flange must be used.For small-diameter pipelines that are frequently disassembled,threaded flanges are used,and blind flanges are used for isolation at the end of pipelines.Regarding the standard system—for domestic trade,use the national standard GB/T or the Ministry of Chemical Industry standard HG/T;for foreign trade,switch to ASME,JIS or DIN according to the customer's region.Even if the DN and pressure level values are the same for flanges of different standards,the bolt hole distribution and thickness may be completely different.Forced mixed installation may make it impossible to assemble at all.

Bonve pump always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.  

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We look forward to working with you to drive efficiency and innovation in industrial fluid transmission with precision technology.