Lap Joint Flange

Lap Joint Flange

The shape of a lap joint flange is similar to a slip on flange; it has a curved radius at the bore that can connect with a stub end fitting and slide over the pipe. The pipe is usually welded to the stub end so that it can freely rotate around the stub end. Lap joint flange and stub end assembly are primarily used in piping systems that must be dismantled frequently for inspection or routine maintenance. To reduce the overall cost of the connection, a stub end will often be made of a special material grade (nickel alloy), with the lap joint made of basic carbon or commodity stainless. Naturally, for uniformity, we recommend that both items be of the same grade. However, your application will determine what is best and/or necessary.

Advantages and Disadvantages 

The composite two-piece construction gives the lap joint flange two clear benefits when in operation. Imagine a lapped joint piping connection where all “wetted” sections must be made of a costly alloy (such as nickel, zirconium, tantalum, or titanium, etc.) to resist corrosion. The pricey, corrosion-resistant alloy can be used to create the stub end. Besides that, common carbon steels can be used to create the flange that serves as the backing flange. Therefore, it is less expensive than an entire alloy flange. On the other hand, it is not physically welded to the pipe. Hence, it may rotate easily to align bolt holes, making assembly and disassembly much simpler. Also, this make it easier to operate a piping system that must frequently be disassembled for inspection or standard maintenance. 

However, the use of the flange has several drawbacks. The flange bore’s internal surface and the stub ends’ external surface have produced fissures that can easily become contaminated. Moreover, the accumulated contaminants might be problematic and cause crevice corrosion. At the design temperature specified by ASME B31.3, the longitudinal strains brought on by pressure, weight, and thermal expansion may build up and surpass the fundamental allowed stress. As a result, it is often utilized in moderate service, where the strains placed on the flange connection by the pipe are minimal. It is because the material of the flange may differ from that of the stub end, galvanic corrosion may occur in some circumstances. 

Usage of Lap Joint Flange 

Typically, low pressure applications require for the usage of the flanges. Hence, it is not appropriate when the flange pair must support heavy weights, Moreover, it may be necessary for some pipes, such as a metal pipe that has previously been lined with plastic. 

Stub End – Key Fittings for Lap Joint Flange

A backing flange for a lap joint is always utilized with a stub end. Stub ends come in three main types: Type A, Type B, and Type C. 

Type A:

The typical lap joint support flange can be machined to accommodate the Type A stub end.

Type B:

The standard slip on flange is intended to be used with Type B stub ends. 

Type C:

The type C stub end can be utilized as either a slip on flange or a lap joint flange. 

Furthermore, stub end patterns can be extensive or short in length. Long pattern ends are also referred to as ASA Stub Ends. The shorter end is used with ANSI 300 and 600’s bigger flanges. They are frequently utilized in sizes ANSI 900 and higher. 

Lap Joint Flange

Differences Between Lap Joint flange and Slip On Flange 

In essence, a slip on flange is a ring that fitted over the pipe end. Additionally, the flange face must be far enough from the pipe’s end to allow for the application of a weld to the inner diameter. Moreover, the slip on flanges outside diameter can be welded to the backside of the flange. Slip on flanges cost less to make and are simpler to align than weld neck flanges. 

Besides that, slip on flange and lap joint flange are quite similar. Also, it almost seems identical from the outside which is the holes and sides of the lap joint flange. However, it has a curved radius on the reverse side to allow the lap joint stub end. On the other hand, the slip on flange can serve as the lap joint flange when type B or type C stub ends are utilized. 

Slip On Flange
Lap Joint Flange

Product Tags

Carbon steel flanges Stainless steel flanges Blind flanges Threaded flanges Socket-weld flange Slip-on flange Lap joint flange Weld neck flange Specialty flange Orifice Flange 1/2″ flange 48″ flange 15mm flange 1200 mm flange 150# flange 300# flange 600# flange 900# flange 1500# flange 2500# flange Raised Face RF Ring Type Joint RTJ Flat Face FF Male &amp Female M&amp F Tongue Groove T&amp G flanges supplier malaysia SCH 10 flange SCH 20 flange SCH 30 flange SCH 40 flange SCH 60 flange SCH 80 flange SCH 100 flange SCH 120 flange SCH 140 flange SCH 160 flange SCH STD SCH XS SCH XXS SCH 10s SCH 40s SCH 80s ASME B16.1 ASME B16.5 ASME B16.20 ASME B16.21 ASME B16.24 ASME B16.34 ASME B16.36 ASME B16.42 ASME B16.47 MSS SP-6 MSS SP-9 MSS SP-25 MSS SP-44 MSS SP-53 MSS SP-54 MSS SP-55 MSS SP-75 MSS SP-106 API 605 API 6A API 6B ASME SA/A105N ASTM ASTM A694 F42 ASTM A694 F46 ASTM A694 F52 ASTM A694 F60 ASTM A694 F65 ASTM A694 F70 ASTM A707 L1 ASTM A707 L2 ASTM A707 L3 ASTM A707 L4 ASTM A707 L5 ASTM A707 L6 ASTM A707 L7 ASTM A707 L8 ASME/ASTM SA/A350 LF1 ASME/ASTM SA/A350 LF2 ASME/ASTM SA/A350 LF3 ASME/ASTM SA/A350 LF6 ASME/ASTM SA/A182F2 ASME/ASTM SA/A182F5 ASME/ASTM SA/A182F9 ASME/ASTM SA/A182F11 ASME/ASTM SA/A182F12 ASME/ASTM SA/A182F22 ASME/ASTM SA/A182F91 ASME/ASTM SA/A182F304/304L


Blind Flange, Slip on Flange, Welding Neck Flange, Socket Weld Flange, Threaded Flange, Lap Joint Flange, Anchor Flange, Orifice Flange

Size Range

1/2" (15mm) - 48" (1200mm)


150#, 300#, 600#, 900#, 1500#, 2500#

Type Available

Raised Face RF, Ring Type Joint RTJ, Flat Face FF, Male & Female M&F, Tongue Groove T&G


SCH 10, SCH 20, SCH 30, SCH 40, SCH 60, SCH 80, SCH 100, SCH 120, SCH 140, SCH 160


SCH 10s, SCH 40s, SCH 80s


ASME B16.1, ASME B16.5, ASME B16.20, ASME B16.21, ASME B16.24,

ASME B16.34, ASME B16.36, ASME B16.42, ASME B16.47

MSS SP-6, MSS SP-9, MSS SP-25, MSS SP-44, MSS SP-53, MSS SP-54, 

MSS SP-55, MSS SP-75, MSS SP-106

API 605, API 6A, API 6B


Carbon Steel


High Yield Carbon Steel

ASTM A694 F42/ 46/ 52/ 60/ 65/ 70

ASTM A707 L1~ L8

Low Temp Carbon Steel

ASME/ASTM SA/A350 LF1/ 2/ 3/ 6

Chrome Moly

ASME/ASTM SA/A182F2, F5 ,F9, F11, F12, F22, F91

Stainless Steel

ASME/ASTM SA/A182F304/304L, 316/316L, 309, 310, 304H, 310H, 317/317L, 321, 321H, 347, 347H, 904L

Duplex/ Super Duplex

UNS S31803, S32205, S32750, S32760
ASME/ASTM SA/A182F51, 53, 55, 60

Nickel Alloy

UNS N02200 (Nickel 200), UNS N02201 (Nickel 201)
UNS N04400 (Monel 400), ), UNS N06600 (Inconel 600)
UNS N06601 (Inconel 601), UNS N06625 (Inconel 625)
UNS N08810 (Incoloy 800H), UNS N08811 (Incoloy 800HT)
UNS N08825 (Inconel 825), UNS N010276 (Hastelloy C276)


HIC, PED 2014/68/EU, NACE MR0175, NORSOK, Weld Overlay available

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