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Flange knowledge
Feb 28, 2017

Flange knowledge

    Any type of connection parts that are closed using bolts at the same time are gerenally referred to flange . The flanges are mainly usded for pipe connections in piping system.According to the type of flange connection,the flange is divided into:Weld neck flange,Slip on flange,blind flange,Lap Joint flange,plate flange,socket flange,threaded flange and so on .

Welding Neck Flanges:

Weld neck flange is different from the other flange because of high neck flange.therefore The welding neck flange is normally known as  the "high hub" Flange.  It is designed to transfer stresses to the pipe, thereby reducing high stress concentrations at the base of the Flange. The welding neck flange is the best designed butt-welded flange of those currently available because of its inherent structural value. The weld neck flange is mainly used in the harsh conditions of the situation,such as pipe thermal expansion or other load leaving the flange stress,or stress changes repeated occasions,pressure,temperature fluctuations in the pipeline and high remperature ,high pressure and below zero temperture of pipeline.

stainless steel welding Neck flange

Threaded (Screwed) Flanges:

The threaded flange is a non-welded flange,and the bore and the hole is threaded.Compared with the weld neck flange,it has the characteristics of installation and maintenance,and it can be used in some occasions,where welding is not allowed. But the threaded flange is not use in the condition whose temperature is above 260℃ or below -45℃ to avoid leakage. 

ASMEB16.5 Thread flange

Slip-On Flanges:

Slip on flange is the same as plate flange,which is also connected with pipes or butt welding fittings through welding.but the pipe or butt welding fittings slips into the flange prior to welding therefore ,the slip on flange has a low hub. It is welded both inside and out to provide sufficient strength and prevent leakage.

stainless steel slip on flange

Lap joint Flanges:  

 The connection of lap joint flange is achieved by welding.The advantage of the lap joint flange is that the flange can be rotated,easily centered on the bold holes ,easy to install on large diameter pipes,and also easy to clean.The lap joint flange is usually identical to a slip-on flange except it has a radius at the intersection of the bore and flange race. This radius is necessary to have the flange accommodate a lap joint stub end. Normally, lap joint flanges and lap joint stub ends are mated together in an assembly system. 

stainlee steel lap joint flanges

Blind Flanges:

The blind flange is a flange which is the middle of flange without a hole. It is used to seal the ends of a piping system and/or a pressure vessel opening. It also permits easy access to the interior of a line or vessel once it has been sealed and must be reopened.The sealing face of blind flange includes raise face ,flat face,ring joint face and so on 

600LB Blind flanges

Socket Welding Flanges:

The socket welding flange is a flange which is connected pipe with bolted,therefore the socket weld flange is always used for pipe or butt welding fittings whose size is less than DN40.The sealing face of socket weld flange includes raise face ,flat face,ring joint face and so on.

304/304L socket welded flanges

 International Standards of steel flange

(1) American Standard

ASME/ANSI B 16.5, ASME B 16.47 SERIES A(MSS SP 44), ASME B 16.47 SERIES B(API 605), ASME B 16.36

(2) British Standard

BS 3293, BS 1560, BS 4504, BS 10

(3) German Standard

DIN2630, DIN2631, DIN2632, DIN2633, DIN2634, DIN2635, DIN2636, DIN2637, DIN2627, DIN2628, DIN2629

(4) Italian Standard

UNI 2280, UNI 2281, UNI 2282, UNI 2283, UNI 2284

(5) Russian, Australian, Japanese & Norwegian Standard

GOST 12821-80, AS2129, JIS B2220 / KS B1503, NOSOK L-005

(6)EN Standard


(7)API Standard


(8)AWWA Standard


(9)China Standard


Material Specification:

Stainless Steel:ASTM A182 F304/304L,F316/316L, ,F321/321H,F347/347H

Carbon Steel:20#,10#,A105,A350LF2,LF3

Super Stainless Steel:ASTM A182 F904L,F317 ,F317L
Low Alloy Steel:ASTM A182F11, F22,F91,F5,F9
Pipeline steel: ASTM A694 F42,F46,F48,F50,F52,F56,F60,F65,F70,F80
Duplex steel:A182 F51(S31803/2205),F53(32750/2507),F44(31254/254MO)

Pressure Ratings:

75LB, 125LB, 150LB, 300LB, 400LB, 600LB, 900LB, 1500LB, 2500LB; 5K, 10K, 16K, 20K, 30K

PN2.5, PN6, PN10, PN16, PN25, PN40, PN64, PN80, PN100, PN250, PN320, PN400