Types and Dimension of SS316 Butt Weld Fittings

In the working environment of pipeline systems with high requirements for the corrosion resistance of pipeline materials, SS316 butt weld fittings have become an important accessory to ensure the safe operation of pipeline systems due to their excellent corrosion resistance, stable performance, and reliable connection effect.

Definition of Stainless Steel Butt Weld Fittings

Stainless steel butt weld fittings are made of high-quality stainless steel materials and manufactured through specific production processes. It is connected to the pipeline through butt welding, achieving functions such as turning, branching, reducing, and sealing of the pipeline system.

Compared with ordinary carbon steel butt weld fittings, the most significant advantage of SS316 butt weld fittings is their excellent corrosion resistance. At the same time, stainless steel material has good toughness and fatigue resistance.

In terms of connection performance, stainless steel butt weld fittings have good sealing performance at the interface formed by welding.

Types and Dimension of SS316 Butt Weld Fittings

Stainless steel butt weld fittings can be divided into various types based on their usage and appearance, such as butt welded elbows, tees, tees, reducers, pipe caps, etc.

The dimensions of SS316 butt weld fittings follow international mainstream standards (such as ASME B16.9, EN10253-4, etc.), and the dimensional parameters mainly include the following key elements. The nominal diameter range is from DN15 (1/2”) to DN2000 (80”), covering the needs of small diameter pipes for household use to large diameter pipes for industrial use; Common wall thickness grades include SCH10, SCH20, SCH40, SCH80, SCH160, etc.

Stainless Steel Butt Weld Elbow

Used for pipeline turning, it can be divided into three angles: 90 deg, 45 deg, and 180 deg. 

90 deg elbow is suitable for vertical turning of pipelines; 

45 deg elbows are commonly used for small angle turning, which can reduce the flow resistance of the medium; 

180 deg elbow is used for pipeline backflow and other purposes.

Dimension of ASME B16.9 Elbow

SS316 Butt Weld Tee

According to the port diameter of the main and branch pipes, they can be divided into equal diameter tees and reducing tees . 

Equal tees are suitable for uniform flow distribution scenarios; 

Reducing tees are suitable for conveying media from main pipelines to small-diameter branch pipelines.

Dimension of BW Tee

ASTM A403 WP316 Butt Weld Reducer

Used to connect pipes of different diameters, divided into concentric reducer and eccentric reducer.

Conc reducer shape is conical, used to increase or decrease the diameter of the center line. It is easy to transport mud and grinding fluid, suitable for corrosive operations, and also beneficial for use in places where different ratings and wear protection are required for transportation between flanges or pipelines.

Ecc reducers are widely used because they can ensure that the pipeline has a same height elevation before and after diameter changes, making it easy to support.

Dimension of Conc and Ecc Reducer

BW End Cap

Used for pipeline end closure, it is divided into flat cap, elliptical cap, and hemispherical cap, which can be selected according to pressure requirements. Flat cap caps are commonly used in low-pressure scenarios, while elliptical or hemispherical caps are preferred in high-pressure scenarios.

Dimension of End Cap

Tolerance of Butt Weld Fittings

The tolerance of welded pipe fittings is a key factor in ensuring the correct installation, alignment, and safe operation of the pipeline system. The tolerance range of ASTM A403 stainless steel butt welded pipe fittings shall comply with the ASME B16.9 standard specification.

TOLERANCES  FOR  BW FITTINGS
Nominal  Size		All Fittings		45 Deg&90 Deg Elbows & Tees, Crosses	3D Radius Elbows	180 Deg Returns			Caps	Reducers & Lap Joint Stub Ends	Lap Joint  Stub Ends
DN	NPS	OD 3) 4)	ID 3)	A   B   C   M	A   B	O	K	U	E,  E1	H   F	G	R	t
15-65	1/2 -21/2	+1.6 -0.8	± 0.8	± 2	± 3	± 6	± 6	±  1	± 3	± 2	0    -1	0    -1	+1.6 0
80-90	3-31/2	± 1.6	± 1.6	± 2	± 3	± 6	± 6	±  1	± 3	± 2	0    -1	0    -1	+1.6 0
100	4	± 1.6	± 1.6	± 2	± 3	± 6	± 6	±  1	± 3	± 2	0    -1	0    -2	+1.6 0
125-200	5-8	+2.4 -1.6	± 1.6	± 2	± 3	± 6	± 6	±  1	± 6	± 2	0    -1	0    -2	+1.6 0
250-450	10-18	+4.0 -3.2	± 3.2	± 2	± 3	± 10	± 6	± 2	± 6	± 2	0    -2	0    -2	+3.2 0
500-600	20-24	+6.4 -4.8	± 4.8	± 2	± 3	± 10	± 6	± 2	± 6	± 2	0    -2	0    -2	+3.2 0
650-750	26-30	+6.4 -4.8	± 4.8	± 3	± 6	---	---	---	± 10	± 5	---	---	---
800-1200	32-48	+6.4 -4.8	± 4.8	± 5	± 6	---	---	---	± 10	± 5	---	---	---
1300-1500	52-60	+6.4 -4.8	± 4.8	± 5	---	---	---	---	---	---	---	---	---
1600-1700	64-68	+6.4 -4.8	± 4.8	± 5	---	---	---	---	---	---	---	---	---
1800-2000	72-80	+6.4 -4.8	± 4.8	± 5	---	---	---	---	---	---	---	---	---

Material Standard for Stainless Steel Butt weld fittings

The material of stainless steel butt welded pipe fittings must comply with strict international standards, and different standards correspond to different stainless steel grades. Common standards include:

ASTM A403: American Society for Testing and Materials standard, covering austenitic stainless steel butt welded fittings, commonly used grades include WP304, WP316, WP316L, etc. It is the most widely used standard in the global industrial field;

EN 10253: EU standard for stainless steel butt welded pipe fittings, divided into EN 10253-2 (carbon steel butt welded pipe fittings) and EN 10253-4 (stainless steel and duplex steel butt welded pipe fittings), suitable for European industrial pipeline systems.

Among them, SS316 welded pipe fittings mainly follow the ASTM A403 WP316 standard, which specifies the chemical composition (such as chromium content of 16% -18%, nickel content of 10% -14%, molybdenum content of 2% -3%), mechanical properties (tensile strength ≥ 515MPa, yield strength ≥ 205MPa), and non-destructive testing requirements of SS316 material, ensuring uniform quality and stable performance of pipe fittings.

Chemical Composition

Mechanical Properties

Advantages of S316 Butt weld fittings

SS316, as a representative grade of austenitic stainless steel, has significantly improved performance compared to ordinary 304 stainless steel. Its core advantages are reflected in the following aspects:

Strong corrosion resistance: SS316 contains 2% -3% molybdenum element, which can significantly enhance its corrosion resistance to chloride ions and withstand the erosion of chloride containing media such as seawater, saltwater, hydrochloric acid, sulfuric acid, etc. In marine engineering, the service life of SS316 butt weld fittings is 2-3 times that of 304 pipe fittings; In the chemical industry, it can be used for long-term transportation of chlorine containing chemical raw materials (such as sodium chloride solution) to avoid damage to pipe fittings due to pitting and crevice corrosion.

Excellent high temperature resistance: SS316 can maintain stable mechanical properties even in high temperature environments (up to 800 ℃), and its strength will not decrease due to high temperature oxidation. It is suitable for high temperature conditions (such as boiler steam pipelines and heat treatment equipment pipelines).

Good low-temperature toughness: Even in a low-temperature environment of -196 ℃, SS316 still has good toughness and no risk of brittle fracture. It can be used in pipeline systems for low-temperature storage and refrigeration equipment (such as liquefied natural gas transmission pipelines).

Strong adaptability: SS316 material has low impurity content (such as sulfur and phosphorus content ≤ 0.03%), smooth and easy to clean surface, will not contaminate the conveying medium, and meets the hygiene standards of the pharmaceutical and food industries (such as drug delivery pipelines in pharmaceutical factories and raw material pipelines in dairy processing factories).

High cost-effectiveness: SS316 can be processed into various types of pipe fittings through forging, stamping, welding and other processes. After welding, the interface strength is high and there is no need for complex post-processing, reducing production and installation costs.

Manufacturing Process

The manufacturing of SS316 butt weld fittings requires multiple precision processes to ensure product accuracy and performance. The core process is as follows:

Raw materials: Stainless steel round bars or steel plates that meet ASTM A403 WP316 standards are selected, and the chemical composition is detected by spectral analysis to ensure that the molybdenum, chromium, and nickel contents meet the standards.

Forming processing: Different forming methods are selected according to the type of pipe fittings - elbows are often made using the "hot pushing" process (stainless steel pipes are heated and pushed into shape through molds to ensure uniform wall thickness); The three-way joint adopts "hydraulic bulging" or "forging forming" (hydraulic bulging forms branches of the pipe blank through high-pressure liquid, while forging forming enhances strength through forging); The reducing pipe adopts "reducing/expanding forming" (reducing or expanding one end of the steel pipe through a mold to achieve the effect of reducing diameter).

Welding treatment: For large-diameter pipe fittings that cannot be seamlessly formed, the "welding forming" process should be used (stainless steel plates are rolled and formed before welding, and argon arc welding is used during welding to reduce oxidation and ensure weld quality). After welding, X-ray inspection should be carried out to check for internal defects in the weld.

Surface treatment: After forming, the pipe fittings need to undergo surface polishing (roughness Ra ≤ 0.8 μ m), acid pickling and passivation (removal of surface oxide skin, formation of passivation film, and enhancement of corrosion resistance). In the pharmaceutical and food industries, pipe fittings also need to undergo electrolytic polishing to further improve surface smoothness.

Quality inspection: After passing the "hydrostatic test" (testing the pressure resistance of pipe fittings to ensure no leakage), "size inspection" (using calipers and micrometers to check diameter and wall thickness tolerances), and "mechanical performance testing" (tensile and impact tests to verify strength and toughness), all inspections must be qualified before leaving the factory.

ASTM A403 Heat Treatment Methods for SS Butt Weld Fittings

Heat treatment is a key step in improving the performance of SS316 butt weld fittings, which can eliminate processing stress and optimize the microstructure. The commonly used heat treatment methods are as follows:

Solution treatment: Heat the pipe fittings to 1050 ℃ -1150 ℃, hold for a period of time, and then quickly cool them with water.

Stabilization treatment: For SS316 variants containing titanium and niobium (such as SS316Ti), stabilization treatment (heating to 850 ℃ -900 ℃, insulation and slow cooling) is required.

Stress relief annealing: After welding, the pipe fittings need to undergo stress relief annealing (heating to 600 ℃ -700 ℃, slow cooling after insulation) to reduce residual stress in the welding area and prevent cracking of the pipe fittings due to stress concentration during use.

Application

With excellent performance, SS316 butt weld fittings have been widely used in the following fields:

Ocean Engineering

chemical industry

medical food

energy industry

Municipal Engineering