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Pipe Fittings Dimensions and Materials

Mar. 31, 2026

Fitting dimensions are always consistent with the connecting pipe dimensions.

Fitting dimensions are related to pipe dimensions and are expressed as nominal pipe size (NPS) and nominal diameter (DN).

Thickness is indicated by the appendix number. Fittings are typically thicker than the pipe to avoid scrap due to thickness reduction during manufacturing. To prevent mismatch between the fitting's inner diameter and the pipe's inner diameter, the manufacturer will bevele the inner edge of the fitting.

Fittings are classified according to their pressure and temperature ratings: Socket weld and threaded joint sizes range from NPS 1/8” to 4”. Weld-to-button fittings are available in the following pressure-temperature ratings:

2000 (threaded fittings only)

3000 and 6000 (two types)

9000 (socket weld joints only)

Standards for checking fitting dimensions:

For pipe fitting products (WP), the following sizes are covered:

ASME B16.9 - Standard for factory-manufactured weld-to-button fittings in NPS 1/₂ to NPS 48” sizes;

ASME B16.28 - Standard for forged steel weld-to-button short-radius elbows and return pipes in NPS 1/₂ to NPS 24” sizes.

For weld-to-button fittings, the following size is covered:

ASME B16.11 - Standard for forged steel fittings, covering both socket weld and threaded fittings.

What should be checked during fitting dimension inspection?

When inspecting pipe fitting dimensions, the following should be confirmed:

Diameter

Length

Thickness chart number

Straightness and perpendicularity of fitting ends

Degree of elbows and bends

Gearbox concentricity

Fit dimensional inspection

Fit material

Fits are always connected to pipes; therefore, the chemical and mechanical properties of these materials must be matched to the pipe materials.

Fits are available in different grades to match pipe materials such as carbon steel, alloy steel, and stainless steel, as well as special materials such as titanium and copper alloys.

ASME B16.9 & 16.28 provide a list of materials used in the manufacture of butt-welded pipe fittings.

ASME B16.34 provides a list of materials used in the manufacture of butt-welded pipe fittings according to ASME B16.11.

ASME B16.9 is the standard for factory-manufactured butt-welded pipe fittings; ASME B16.28 is the standard for butt-welded short-radius elbows and bends;

ASME B16.11 is the standard for forged steel socket weld and threaded fittings. It refers to another ASME material standard, ASME B16.34, for flanges, threads, and welded-end valves.

If fittings are manufactured according to ASME B16.9 and B16.28, the material grade should be prefixed with WP.

This section lists commonly used material grades for pipe fittings:

For carbon steel: - ASTM A234 Gr.WPA/B, ASTM A420 Gr.WPL6

For alloy steel: - ASTM A234 WP1 / WP5 / WP7 / WP9 / WP11 / WP12 / WP22

For stainless steel: - ASTM A403 WP304 / WP304L / WP304H / WP316 / WP316L / WP321 / WP347

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Industry News

Mar. 31, 2026

Pipe Fittings Dimensions and Materials

Fitting dimensions are always consistent with the connecting pipe dimensions. Fitting dimensions are related to pipe dimensions and are expressed as nominal pipe size (NPS) and nominal diameter (DN).
Industry News

Mar. 25, 2026

Are seamless steel pipe production subject to policy restrictions?

In recent years, an increasing number of customers and industry practitioners have asked: Is seamless steel pipe production subject to policy restrictions?

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