ASME B16.5 Flange General Introduction

ASME B16.5 is the most commonly used international standard for pipe flanges and flanged fittings. It defines dimensions, pressure ratings, materials, tolerances, and testing requirements for flanges used in pressure piping systems. ASME B16.5 flanges provide high compatibility and reliability for various industrial applications.

ASME B16.5 Lap Joint Flange

The ASME B16.5 lap joint flange is a loose-type flange that is not directly welded to the pipe. It can rotate freely, making bolt hole alignment much easier during installation. ASME B16.5 lap joint flange is usually used together with lap joint stub end to form a complete and practical flanged connection.

Class 150 Dimension of ASME B16.5 Lap Joint Flange

Class 150 is the most popular pressure class for ASME B16.5 lap joint flange. All Class 150 dimensions strictly comply with ASME B16.5 standard. Unified dimensions ensure good interchangeability between different manufacturers.

Sealing faces of Lap Joint Flange

Sealing faces directly affect the sealing performance of lap joint flanges. ASME B16.5 lap joint flanges provide three main types of sealing faces:

• Raised Face (RF)
• Flat Face (FF)
• Ring Type Joint (RTJ)

Raised Face (RF) is the most widely used for Class 150 and Class 300 lap joint flanges, providing strong and reliable sealing for most general industrial piping systems.

Flat Face (FF) is mainly used in low-pressure Class 150 systems, often matched with cast iron equipment or non-metallic flanges.

Ring Type Joint (RTJ) is designed for high-pressure classes Class 600 and higher, using metal ring gaskets for high-temperature and high-pressure service conditions.

ASME B16.5 LAPJ Flange Weight Reference

Weight information is important for transportation, installation, and structural design. The weight of ASME B16.5 lap joint flange changes with nominal pipe size, material, and pressure class. Accurate weight data helps users estimate logistics cost and project load.

ASME B16.9 Standard

ASME B16.9 is the standard for factory-made wrought steel butt-welding fittings. It covers dimensions, manufacturing requirements, and inspection rules for butt-welding fittings such as elbows, tees, reducers, and lap joint stub ends. ASME B16.9 ensures stable fitting quality and good matching with pipes.

ASME B16.9 Lap Joint Stub End

ASME B16.9 lap joint stub end is a special butt-welding fitting designed for lap joint flanges. It has a straight pipe body and a flared end that forms the sealing surface. The stub end is welded to the pipe, while the lap joint flange remains rotatable.

How Lap Joint Flange Works with Stub End?

Understanding how lap joint flange works with stub end helps ensure correct installation.

The lap joint flange is first slipped onto the pipe. The stub end is then welded to the pipe end. The flange can rotate freely for easy bolt alignment. When tightened, the flange holds the stub end to create a strong and tight connection.

Material Selection for Lap Joint Flange and Stub End

Material is key to the service life and safety of lap joint flange and stub end. Common materials include:

• Carbon steel
• Stainless steel 304/304L
• Stainless steel 316/316L
• Alloy steel

Materials are chosen based on pressure, temperature, medium, and corrosion resistance needs. The stub end is often made of the same material as the pipeline.

Typical Applications

Lap joint flange and stub end connections are widely used in many industries due to easy installation and maintenance. Typical applications include:

• Chemical and petrochemical plants
• Water treatment systems
• Food and beverage processing
• Pharmaceutical equipment
• Marine and offshore piping
• Stainless steel piping systems

They are especially suitable for systems that require frequent disassembly and cleaning.

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ASME B16.9 defines the technical requirements for butt weld pipe fittings made from carbon steel, alloy steel, and stainless steel, covering dimensions, tolerances, marking, testing, and material properties. In particular, the dimensional accuracy of Lap Joint Stub Ends—including carbon steel stub ends and stainless steel stub ends—directly affects the sealing integrity, pressure-bearing capacity, and overall adaptability of the piping system. Therefore, these parameters are closely monitored by engineers, procurement teams, and construction personnel alike.

In addition to ASME B16.9, the MSS SP-43 standard also applies to Stub Ends and other wrought stainless steel butt weld fittings, particularly for lightweight and corrosion-resistant applications. While ASME B16.9 primarily covers fittings designed for higher pressure and heavier wall thicknesses, MSS SP-43 specifies dimensions for fittings with schedule 5S, 10S, and 40S wall thicknesses, commonly used in low-pressure or non-critical stainless steel piping systems.

By understanding the relationship between ASME B16.9 and MSS SP-43, industry professionals can accurately select the proper Stub End type based on pressure rating, material grade, and installation requirements—ensuring both performance and cost-effectiveness in pipeline design and construction.

Butt Weld Stub End Specification

ASME B16.9 Standard

This Standard covers overall dimensions, tolerances, ratings, testing, and markings for wrought factory-made buttwelding fittings in sizes NPS 1;2 through 48 (DN 15 through 1200).

Generally speaking, the maximum size of a stub end is 24 inches. This is because it is often used with a lap joint flange. According to the ASME B16.5 standard, the maximum size range of a lap joint flange is only 24 inches. Therefore, the size of the stub end is also limited to this range.

A Stub End is a common butt weld pipe fitting typically used with Lap Joint Flanges. One end is designed for butt welding to steel pipes, while the other features a flanged structure for mating with lap joint flanges.

Stub Ends are categorized into Short Pattern and Long Pattern based on length, with dimensions specified by the ASME B16.9 standard.

Long Pattern Stub End Dimensions

Short Pattern Stub End Dimensions

Stainless Steel Lap Joint Stub End Tolerance as per ASME B16.9

MSS SP-43 Standard

MSS SP-43 standard lap joint stub ends are available in sizes ranging from NPS ½ to NPS 24. Manufactured from stainless steel, MSS SP-43 stub ends are suitable for use with Schedule 5S and Schedule 10S pipes, while stub ends are compatible with Schedule 40S pipes. MSS Type A stub ends conform to industry specifications for use with standard flat lap flanges.

MSS SP-43 Stub End Dimensions

Lap Joint Stub End Weights

Stub End Material

Stainless Steel Buttweld Long Stub End :
ASTM A403 WP316/316L, ASTM A403 SA / A 774 WP-S, WP-W, WP-WX 304/304L, ASTM A182 F316L, 304L, DIN 1.4301, DIN1.4306, DIN 1.4401, DIN 1.4404

Duplex & Super Duplex Steel Buttweld Long Stub End :
ASTM A 815, ASME SA 815 UNS NO S31803, S32205. UNS S32750, S32950. Werkstoff No. 1.4462

Carbon Steel Buttweld Long Stub End :
ASTM A234, ASME SA234 WPB , WPBW, WPHY 42, WPHY 46, WPHY 52, WPH 60, WPHY 65 & WPHY 70.

Low Temperature Carbon Steel Buttweld Long Stub End : 

ASTM A420 WPL3/WPL6

Alloy Steel Buttweld Long Stub End :
ASTM / ASME A/SA 234 Gr. WP 1, WP 5, WP 9, WP 11, WP 12, WP 22, WP 91

Nickel Alloy Buttweld Long Stub End :
ASTM B336, ASME SB336, Nickel 200 (UNS No. No2200), Nickel 201 (UNS No. N02201), Monel 400 (UNS No. N04400), Monel 500 (UNS No. N05500), Inconel 800 (UNS No. N08800), Inconel 825 (UNS No. N08825), Inconel 600 (UNS No. N06600), Inconel 625 (UNS No. N06625), Inconel 601 (UNS No. N06601), Hastelloy C 276 (UNS No. N10276), Alloy 20 (UNS No. N08020), Titanium (Grade I & II), Cupro-Nickel 70/30, CuNi10Fe1Mn, CuNi30Mn1Fe.

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Lap Joint Stub End Specification

Performance Characteristics:

Convenient Connection: by cooperating with loose-set flange and adopting bolt connection, it is convenient to install and dismantle, which facilitates the maintenance and replacement of pipeline.

Good sealing: Utilizing the flange sealing structure, it can effectively prevent medium leakage and guarantee the safe operation of the pipeline system.

Strong adaptability: it can be applied to pipeline systems with a variety of media and temperature conditions, and can be used under different working conditions in petroleum, chemical, natural gas and other industries.

Types of Lap Joint Stub End

Type A

Type A stub ends are used for standard lap joint flanges. The lap thickness at the stub end is greater than or equal to the nominal thickness of the pipe wall. In addition, Type A has an outside corner radius to accept lap flanges. The inside corners are square. The lap usually has a machined serrated face.

Type B

Type B short ends are used as lap joint flanges for standard slip on flanges. The lap thickness of these short ends is greater than or equal to the nominal thickness of the pipe wall. In addition, the outside corner radius of Type B is small enough to accommodate a slip-on flange that can be used as a backup flange. The inside corners are square. The lap usually has a machined serrated face.

Type C

Type C stumps are available for standard lap joint flanges and slip-on flanges. It is flared with a rounded edge at the lap ID. If necessary, the radius can be squared. The lap thickness is 75% of the pipe wall. type C pipe is short enough to accommodate any spare flanges. type C laps are smooth and do not require machining.

You can view the exact specifications on our [Stub End Type A] product detail page.

Long Pattern Stub End and Short Pattern Stub End

1. Long Pattern Stub End

The Long Pattern Stub End usually has a long straight section, which makes it excellent in applications where a long connection length is required or where there are special requirements for pipe support. It provides better stability and reduces the effects of pipe vibration or displacement.

Advantage:

Smoother Fluid Paths: Longer straight sections of pipe help reduce turbulence in the transition to the flanged connection, providing a smoother fluid flow. This is especially important for systems with stringent requirements for fluid resistance or pressure loss.

Better welding conditions: Longer lengths provide more maneuvering space for welding, especially when welding in the field.

2. Short Pattern Stub End

Short Pattern Stub Ends are relatively compact, with short straight sections that are advantageous in space-constrained installations, allowing greater flexibility in adapting to pipe connections in confined spaces.

Advantage:

Space-saving: Due to their compact construction, short flanged short sections are very popular in piping layouts where space is limited.

Lighter weight: Shorter lengths mean less material is used, reducing weight and costs.

Wider applicability: In applications with less demanding hydrodynamic requirements, the Short Flap is a more economical and practical choice.

Material & Grades of Buttweld Lap Joint Stub End :

Stainless Steel Buttweld Lap Joint Stub End :
A403 WP304/304L/304H – WP316/316L – WP317 – WP310S – WP321 – WP347 – WP904L  

Duplex & Super Duplex Steel Buttweld Lap Joint Stub End :
A815 WPS32205/32750/31803/32760

Carbon Steel Buttweld Lap Joint Stub End :
ASTM A234 WPB / WPC, ASTM 420 WPL 3 / 6 / 9, A860 WPHY 42 / 46 / 52 / 56 / 65 / 70   

Alloy Steel Buttweld Lap Joint Stub End :
A234 WP5 / WP9 / WP11 / WP12 / WP22 /WP 91 / WP92

Nickel Alloy Buttweld Lap Joint Stub End :
ASTM B336, ASME SB336, Nickel 200 (UNS No. No2200), Nickel 201 (UNS No. N02201), Monel 400 (UNS No.N04400), Monel 500 (UNS No. N05500), Inconel 800 (UNS No. N08800), Inconel 825 (UNS No. N08825), Inconel600 (UNS No. N06600), Inconel 625 (UNS No. N06625), Inconel 601 (UNS No. N06601), Hastelloy C 276 (UNS No.N10276), Alloy 20 (UNS No. N08020), Titanium (Grade I & II), Cupro-Nickel 70/30, CuNi10Fe1Mn, CuNi30Mn1Fe.

Dimensions of ASME B16.9 Lap Joint Stub End

Advantages of Stub Ends

Cost-effective: Where expensive, corrosion-resistant materials (e.g. stainless steel, nickel alloys) are used in the piping system, they can be used only in the part of the stub end that comes into contact with the fluid, whereas the more economical carbon steel can be used for the loose-fitting flange. This significantly reduces the cost of the overall flanged connection.

Ease of installation and maintenance: The free rotation of the flanged stub makes alignment of the bolt holes extremely simple, greatly simplifying the installation process. It is also easier to disassemble and reassemble when equipment needs to be inspected or replaced, eliminating the need for cutting or rewelding.

Adaptable: It is easy to connect pipes made of different materials. For example, corrosion-resistant flanged short sections are used for corrosive fluids, while ordinary carbon steel pipes are used for other sections.

Stress Reduction: The flexibility of the loose flange helps to relieve stresses in the piping system due to thermal expansion or vibration, thereby extending the life of the piping system.

Applications

Equipment connections that require frequent disassembly: heat exchangers, vessels, pumps, valves

Corrosive media piping systems: in pipelines handling corrosive fluids such as acids, alkalis, brines, etc.

Oil and gas industry: oil and gas transportation, refinery equipment.

Chemical industry: various chemical production lines.

Power industry: especially in nuclear power plants and other occasions with strict material requirements.

Food and pharmaceutical industry: piping systems with high requirements for hygiene and cleanliness.

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