Butt Welded Pipe Fittings

What are Butt Weld Fittings?

Butt weld fittings are pipe fittings with beveled ends that connect to pipelines via full penetration welding. This connection method offers high strength and excellent sealing, making it the most common connection method in industrial piping systems.

Butt weld fittings can be manufactured using seamless or welded steel pipes, primarily made of carbon steel, stainless steel, alloy steel, and duplex steel. Compared to threaded or socket weld connections, butt weld connections are suitable for higher pressure and temperature conditions.

Classification of Butt Weld Fittings:

Butt weld fittings are classified by function as follows:

1. Elbow: Used to change the direction of a pipe. Classified by bending radius:
● Long radius elbow (LR, R=1.5D): Low flow resistance, most commonly used.
● Short radius elbow (SR, R=1.0D): Compact structure, used when space is limited.
Classified by angle: 45°, 90°, 180° elbows.

2. Tee: Used for branch pipe connections. Classified by diameter:
● Equal diameter tee: Three tees of the same diameter.
● Reducing tee: Main and branch pipes have different diameters.
Classified by shape: Straight tee, Y-tee.

3. Reducer: Used to connect pipes of different diameters. Classified by structure:
● Concentric reducer: Centerline is on the same straight line, suitable for vertical pipes.
● Eccentric reducer: Bottom or top flush, suitable for horizontal liquid pipes (flat bottom) or gas pipes (flat top).

4. Cap: Used to seal the end of a pipe. According to shape, they are divided into:
● Elliptical caps: The generatrix is semi-elliptical, with a major axis:minor axis ratio of 2:1. They have strong pressure-bearing capacity and are the most widely used.
● Flat-bottomed caps: Simple to manufacture and low in cost, suitable for applications with DN≤100 and pressure below 1.0MPa.

Common Specifications for Butt-welded Pipe Fittings:

a. Size range: 

Parameter	Range
Nominal Diameter (DN)	DN15 — DN2000
Imperial Size (NPS)	1/2 inch — 80 inch

b. Wall thickness grade (Sch):

● Thin-walled series: Sch10s, Sch20, Sch30
● Standard series: STD, Sch40, Sch40s
● Thick-walled series: XS, Sch80, Sch80s
● Extra-thick-walled series: Sch160, XXS

△The two most commonly used grades are STD (standard wall thickness) and XS (thick-walled).

Common Materials and Standards for Butt-welded Pipe Fittings:

Material type	Common Steel Grades
Carbon Steel	ASTM A234 WPB
High-Strength Carbon Steel	ASTM A860 WPHY42, 52, 60, 65, 70
Low-Temperature Carbon Steel	ASTM A420 WPL3, WPL6, WPL9
Stainless Steel	ASTM A403 WP304, WP316, WP321, WP347 ASTM A403
Alloy Steel	ASTM A234 WP1, WP5, WP9, WP11, WP12, WP22, WP91
Duplex Stainless Steel	ASTM A815 S31803, S32205, S32550, S32750, S32760

Common Standards for Butt-Welded Pipe Fittings:

American Standards (ASME/ANSI):

Standard Number	Name
ASME B16.9	Factory-Made Steel Butt-Welded Pipe Fittings
ASME B16.28	Steel Butt-Welded Short Radius Elbows and Back Bends
MSS SP-43	Forged Stainless Steel Butt-Welded Pipe Fittings (Thin Wall)

Standards for Socket Welding and Threaded Pipe Fittings (Small Diameter):

Standard Number	Name
ASME B16.11	Socket Welding and Threaded Forged Pipe Fittings
MSS SP-83	Socket Welding and Threaded Unions
MSS SP-97	Integral Reinforced Pipe Seats

Chinese Standards (GB):

GB/T 12459-2017: Types and Parameters of Steel Butt-Welded Pipe Fittings (General for Seamless and Welded Fittings)
GB/T 13401-2017: Steel Plate Butt-Welded Pipe Fittings (For Welded Fittings Only)

SH 3408: Steel Butt-Welded Seamless Pipe Fittings (Petrochemical Industry Standard)
SH 3409: Steel Plate Butt-Welded Pipe Fittings (Petrochemical Industry Standard)
DL/T 695: Steel Butt-Welded Pipe Fittings for Power Plants (Power Industry Standard)

Butt-welded Pipe Fittings vs. Seamless Pipe Fittings:

Butt-welded pipe fittings refer to the connection method (butt welding with beveled ends), while seamless pipe fittings refer to the manufacturing process (no weld seam). They are different categories. Butt-welded pipe fittings can be seamless or welded.

Butt-welded Pipe Fittings vs. Socket-welded Pipe Fittings: How to Choose?

The main difference between butt-welded pipe fittings (ASME B16.9) and socket-welded pipe fittings (ASME B16.11) lies in the connection method and applicable scenarios. The following factors should be considered when selecting fittings:

1. Selection by Diameter:
Butt-welded fittings: Suitable for any diameter, from DN15 to DN2000.
Socket-welded fittings: Only suitable for small diameters, typically below DN100, with DN50 and below being the most common.

2. Selection by Pressure:
Butt-welded fittings: Suitable for various working conditions, including high, medium, and low pressure; high strength with full penetration welds.
Socket-welded fittings: Suitable for medium and high pressure conditions, but fillet weld strength is lower than butt-welded fittings.

3. Selection by Temperature and Medium:
Butt-welded fittings: Suitable for high-temperature, low-temperature, and corrosive media; weld strength can be equal to that of the base material.
Socket-welded fittings: Suitable for general working conditions; not recommended for applications with severe temperature cycling.

4. Selection by Installation Space:
Butt-welded fittings: Require a larger welding operation space.
Socket-welded fittings: Compact installation, suitable for space-constrained applications.

Selection Recommendation: Prioritize butt-welded fittings due to their higher connection strength and wider applicability. Only consider socket-welded fittings for diameters below DN50, in space-constrained situations, or for rapid installation. 

What is the Difference between Sch40 and Sch40s?

Sch40: Used for carbon steel elbows (e.g., ASTM A234 WPB)
Sch40s: The "s" stands for Stainless Steel, used for stainless steel elbows (e.g., ASTM A403 WP304/316)

Read more: Stainless steel fittings vs. Carbon steel fittings or Class 3000 vs. Class 6000 Socket Weld Fittings