S31803 Threaded Elbow, Tee and Cross Specifications

S31803, a premium Duplex stainless steel. When machined into threaded fittings like elbows, tees, and crosses. Under the ASTM A182 material specification and manufactured to the dimensional and pressure standards of ASME B16.11, S31803 threaded fittings deliver a superior combination of strength and corrosion resistance.

S31803 Threaded Elbow Tee and Cross Specifications

This guide details the specifications, key dimensions, and proper selection criteria for threaded elbows, tees, and crosses made from this robust alloy.

S31803 is a ferritic-austenitic stainless steel. It features a balanced microstructure of approximately 50% ferrite and 50% austenite, which provides significant advantages over conventional stainless steels:

High Strength: Its yield strength is roughly double that of standard 316 austenitic stainless steel.

Excellent Corrosion Resistance: It offers superior resistance to stress corrosion cracking, pitting, and crevice corrosion, particularly in chloride-containing environments.

The ASME B16.11 standard covers ratings, dimensions, tolerances, marking, and material requirements for forged fittings. For threaded S31803 fittings, the focus is on two primary pressure classes: Class 2000, 3000, and 6000.

Scope of ASME B1611 for Threaded Fittings

1. S31803 Threaded Elbows (45° and 90°)

Elbows are used to change the direction of the pipeline.

Dimensions: Available in nominal pipe sizes (NPS) from 1/8" to 4".

Precision: The threading (usually NPT) must be cut with high precision to ensure a leak-proof seal. The "Center-to-End" dimension is the critical specification here to ensure the piping layout aligns perfectly.

2. S31803 Threaded Tees and Crosses

Tees (3-way) and Crosses (4-way) are used for branching the flow within a system.

Geometry: These fittings must maintain a consistent wall thickness throughout the body to handle the turbulence and pressure changes that occur at junctions.

Symmetry: ASME B16.11 dictates strict tolerances on the "Center-to-End" dimensions for all outlets to ensure the grid remains square and true during assembly.

Elbows change the direction of a piping run. Key dimensions include Center-to-End (Dimension A for 90°, C for 45°) and the Outside Diameter of the Band (D).

Table 1: Dimensions for S31803 Threaded 90° Elbows (Selected Sizes)

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Nominal size		Center to end						Outside diameter to band			Wall thickness			Length of thread
DN	NPS	A						H			G_min			L5_min	L2_min
		90° Elbows			45° Elbows			H			G_min
		2000	3000	6000	2000	3000	6000	2000	3000	6000	2000	3000	6000
6	1/8	21	21	25	17	17	19	22	22	25	3.18	3.18	6.35	6.4	6.7
8	1/4	21	25	28	17	19	22	22	25	33	3.18	3.30	6.60	8.1	10.2
10	3/8	25	28	33	19	22	25	25	33	38	3.18	3.51	6.98	9.1	10.4
15	1/2	28	33	38	22	25	28	33	38	46	3.18	4.09	8.15	10.9	13.6
20	3/4	33	38	44	25	28	33	38	46	56	3.18	4.32	8.53	12.7	13.9
25	1	38	44	51	28	33	35	46	56	62	3.68	4.98	9.93	14.7	17.3
32	1_1/4	44	51	60	33	35	43	56	62	75	3.89	5.28	10.59	17.0	18.0
40	1_1/2	51	60	64	35	43	44	62	75	84	4.01	5.56	11.07	17.8	18.4
50	2	60	64	83	43	44	52	75	84	102	4.27	7.14	12.09	19.0	19.2
65	2_1/2	76	83	95	52	52	64	92	102	121	5.61	7.65	15.29	23.6	28.9
80	3	86	95	106	64	64	79	109	121	146	5.99	8.84	16.64	25.9	30.5
100	4	106	114	114	79	79	79	146	152	152	6.55	11.18	18.67	27.7	33.0

Tees allow for branch connections. The primary dimension is the Center-to-End (A) length, measured from the centerline of the run to the end of the branch outlet.

Crosses provide a four-way connection. Like tees, they are measured Center-to-End (A) and are available in equal (all outlets same size) and unequal configurations.

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Nominal size		Center to end			Outside diameter to band			Wall thickness			Length of thread
DN	NPS	A			H			G_min			L5_min	L2_min
		Tees and Crosses			H			G_min
		2000	3000	6000	2000	3000	6000	2000	3000	6000
6	1/8	21	21	25	22	22	25	3.18	3.18	6.35	6.4	6.7
8	1/4	21	25	28	22	25	33	3.18	3.3	6.6	8.1	10.2
10	3/8	25	28	33	25	33	38	3.18	3.51	6.98	9.1	10.4
15	1/2	28	33	38	33	38	46	3.18	4.09	8.15	10.9	13.6
20	3/4	33	38	44	38	46	56	3.18	4.32	8.53	12.7	13.9
25	1	38	44	51	46	56	62	3.68	4.98	9.93	14.7	17.3
32	1 ₁_/₄	44	51	60	56	62	75	3.89	5.28	10.59	17	18
40	1₁_/₂	51	60	64	62	75	84	4.01	5.56	11.07	17.8	18.4
50	2	60	64	83	75	84	102	4.27	7.14	12.09	19	19.2
65	2 ₂_/₁	76	83	95	92	102	121	5.61	7.65	15.29	23.6	28.9
80	3	86	95	106	109	121	146	5.99	8.84	16.64	25.9	30.5
100	4	106	114	114	146	152	152	6.55	11.18	18.67	27.7	33

Selecting the correct fitting involves more than just matching pipe sizes. Consider these factors:

Pressure Class: This must be selected to meet or exceed the maximum operating pressure of your system. Higher classes (6000 LBS) have thicker walls and larger outside diameters.

Thread Type: Ensure compatibility with your piping. The most common is NPT (National Pipe Tapered), but BSP (British Standard Pipe) threads are also widely available.

Size Range: S31803 threaded fittings are typically available from NPS 1/8" up to 4", with availability across all pressure classes within that range.

Standards Compliance: Confirm fittings meet ASTM A182 for material and ASME B16.11 for dimensions. Complementary standards like MSS SP-79 and BS 3799 may also apply.

At our facility, we ensure that every S31803 fitting adheres to ASME B1.20.1 for pipe threads. Because Duplex stainless steel is harder to machine than standard grades, we use specialized tooling to prevent "galling". This ensures that when your team installs these fittings on-site, the connection is smooth, tight, and reliable.

Would you like me to provide a detailed quote for specific sizes, or would you prefer a technical data sheet comparing S31803 to Super Duplex S32750?