What are lap joint flanges?

What are lap joint flanges?

Lap Joint Flanges (LJ Flanges) or Loose flanges (LF flanges) called are used on piping fitted with lapped pipe or with lap joint stub ends the combined initial cost of the two items being approximately one-third higher than that of comparable welding neck flanges. Their pressure-holding ability is little, if any, better than that of slip-on flanges and the fatigue life of the assembly is only one-tenth that of welding neck flanges. The lap joint flange with the stub end assembly are normally used in systems requiring frequent dismantling for inspection and cleaning and where the ability to swivel flanges and to align bolt holes materially eases the erection of large diameter or unusually stiff piping. Lap Joint flanges have certain special advantages:Freedom to swivel around the pipe facilitates the lining up of opposing flange bolt holes.Lack of contact with the fluid in the pipe often permits the use of inexpensive carbon steel flanges with corrosion resistant pipe. In systems which erode or corrode quickly, the flanges may be salvaged for re-use.

Lap Joint Flanges have all the same common dimensions as any other flange named on this page however it does not have a raised face, they used in conjunction with a "Lap Joint Stub End".

Lap Joint Flanges are nearly identical to a Slip On flange with the exception of a radius at the intersection of the flange face and the bore to accommodate the flanged portion of the Stub End.

Their pressure-holding ability is little, if any, better than that of Slip On flanges and the fatigue life for the assembly is only one tenth that of Welding Neck flanges.

They may be used at all pressures and are available in a full size range. These flanges slip over the pipe, and are not welded or otherwise fastened to it. Bolting pressure is transmitted to the gasket by the pressure of the flange against the back of the pipe lap (Stub End).

Lap Joint flanges have certain special advantages:

• Freedom to swivel around the pipe facilitates the lining up of opposing flange bolt holes.
• Lack of contact with the fluid in the pipe often permits the use of inexpensive carbon steel flanges with corrosion resistant pipe.
• In systems which erode or corrode quickly, the flanges may be salvaged for re-use.

Lap Joint Flanges are always used with either a stub end or taft which is butt welded to the pipe with the flange loose behind it. This means the stub end or taft always makes the face. The lap joint is favoured in low pressure applications because it is easily assembled and aligned.

Size

Lap Joint Flanges (Loose Flanges): 3/8″-80″

                                                DN10-DN2000

Pressure

America Series:Class 150 ,Class 300, Class 600, Class 900A ,Class 1500,Class 2500.

Europe Series:PN2.5,PN6,PN10,PN16,PN25,PN40,PN63,PN100,PN160,PN250,PN320,PN400.

 

Flange Facing Types

America Series:Flat face(FF),Raised face(RF),Tongue(T),Groove(G),Female(F),Male(M),Ring type joints face(RJ/RTJ)

Europe Series:Type A(Flat Face),Type B(Raised Face),Type C(Tongue),Type D(Groove),Type E(Spigot),Type F(Recess),Type G(O-Ring Spigot),Type H(O-Ring Groove)

 

Material

Carbon steel: ASTM A105,ASTM A105N,GB 20,C22.8.

Alloy steel: ASTM/ASME A234 WP 1-WP 12-WP 11-WP 22-WP 5-WP 91-WP 911

Stainless steel: ASTM/ASME A403 WP 304-304L-304H-304LN-304N

ASTM/ASME A403 WP 316-316L-316H-316LN-316N-316Ti

ASTM/ASME A403 WP 321-321H ASTM/ASME A403 WP 347-347H

Low temperature steel: ASTM/ASME A402 WPL 3-WPL 6

High performance steel: ASTM/ASME A860 WPHY 42-46-52-60-65-70

 

Standards

ASME ANSI B16.5,ASME ANSI B16.47.

API 605,API 6L.

MSS SP 44

CSA Z245.12

EN1092-1,EN1759-1.

DIN2642,DIN2655,DIN2656.

BS1560,BS 4504,BS 10.

AFNOR NF E29-200-1

ISO7005-1

AS2129

JIS B2220

UNI 2276. UNI 2277.UNI 2278 .UNI 6089 .UNI 6090

Industrial Processes

Die forging,Machining.

Application for Lap Joint flange(LJ flange) /Loose flanges

Natural gas,chemical,petroleum,ship building,marine,paper making, metallurgy, electric, power, boiler , etc.

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