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Fluid conduction · Pipe fittings
TECHNICAL DATA SHEET
FT-TC-ACC-BW-001
Issue date: July 28, 2026 · Rev. 001

ASME B16.9 butt weld fittings — ASTM A234 WPB carbon steel and ASTM A403 WP304/WP316 stainless (elbows, 45s, tees, reducers and caps)

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A butt weld fitting is a wrought fitting with dimensions standardized by ASME B16.9, welded to the pipe with a beveled butt joint per ASME B16.25. Its wall is that of the schedule it is ordered with (ASME B36.10M for carbon steel, B36.19M for stainless) and its allowable pressure is, by rule of the standard itself (B16.9-2018, para. 2.1), the one computed for seamless pipe of equivalent material and that same schedule. This sheet consolidates the center-to-face in millimeters and inches of every figure in the catalog — 90-deg long and short radius elbows, 45-deg elbows, 180-deg returns, tees, concentric and eccentric reducers and caps — from 1/2 to 12 in, in ASTM A234 WPB carbon steel (schedules 40 and 80) and ASTM A403 WP304/WP316 stainless (schedules 10S and 40S): 17 catalog references covered by a single data sheet.

Center-to-face, 4″ long radius 90-deg elbow
152 mm
6.00 in — rule A = 1.5 × NPS from 1″ up (ASME B16.9-2018, Table 6.1-1)
Fitting allowable pressure
= that of the pipe
Rated as seamless pipe of its schedule and material (B16.9-2018, para. 2.1) — e.g. 4″ sch 40 A234 WPB: 127 bar at ≤38 °C (FT-TC-TUB-SCH40-001)
Family materials
A234 WPB · A403 WP304/316
Minimum yield 240 MPa (WPB) and 205 MPa (WP304/WP316); tensile 415–585 and ≥515 MPa
Dimensional and end-prep standard
ASME B16.9 + B16.25
B16.9 covers NPS 1/2–48 in; published catalog 1/2–12 in · 37.5 deg +2.5/−0 bevel with 1.6 ± 0.8 mm root face

Important: Before using these data in engineering, design or installation decisions on systems exposed to mechanical, pressure, rupture, fatigue, impact or water-hammer risk, it is essential to read the technical notice and limitation of liability at the end of this sheet.

SKU VT-58731 (90-deg long radius carbon steel butt weld elbow, sch 40) · family of 17 references: carbon steel sch 40/80 (90-deg elbow, 45-deg elbow, tee, concentric and eccentric reducer, cap) and stainless sch 10/40 (90-deg elbow, 45-deg elbow, tee, concentric reducer, cap) · 90-deg sch 40 elbow from COP $2,100 + VAT per unit (Jul 2026, confirmed on quotation)

1. ASME B16.9 butt weld fitting dimensions (mm and inches)

ASME B16.9 fixes the position of the welding ends with respect to the fitting centerline: the center-to-face is the distance from the geometric center to the beveled face, and it is the figure that defines how much room the fitting takes on the isometric. The tables below reproduce the ASME B16.9-2018 values (Tables 6.1-1, 6.1-3, 6.1-4, 6.1-7, 6.1-10 and 6.1-11) from 1/2 to 12 in — the TECTUL catalog range. In this catalog, «codo» is the 90-deg long radius elbow and «semicodo» is the 45-deg elbow (column B).

Elbows and returns — center-to-face per size

NPSOutside Ø at bevel90-deg LR elbow, A45-deg elbow, B90-deg SR elbow, A180-deg LR return
mminmminmminmminO (mm)K (mm)
1/2″21.30.84381.50160.627648
3/4″26.71.05381.50190.757651
1″33.41.32381.50220.88251.007656
1-1/4″42.21.66481.88251.00321.259570
1-1/2″48.31.90572.25291.12381.5011483
2″60.32.38763.00351.38512.00152106
2-1/2″73.02.88953.75441.75642.50190132
3″88.93.501144.50512.00763.00229159
4″114.34.501526.00642.501024.00305210
5″141.35.561907.50793.121275.00381262
6″168.36.622299.00953.751526.00457313
8″219.18.6230512.001275.002038.00610414
10″273.010.7538115.001596.2525410.00762518
12″323.812.7545718.001907.5030512.00914619

Values from ASME B16.9-2018, Tables 6.1-1 (90-deg LR and 45-deg elbows), 6.1-4 (short radius: the standard tabulates it from NPS 1″ up) and 6.1-3 (180-deg long radius returns: O is center-to-center and K is back-to-face; return A = O/2, Note 2 to Table 6.1-3). The 180-deg short radius return exists from NPS 1″ with O = 2 × the 90-deg SR elbow (Table 6.1-5).

Tees, reducers and caps — per size

NPSStraight tee, C = M (center-to-face, run and outlet)Conc./ecc. reducer, H (face-to-face, by large end)Cap, E (length)Heavy-wall cap, E1 (mm)Limiting wall for E (mm)
mminmminmmin
1/2″251.00251.00254.57
3/4″291.12381.50251.00253.81
1″381.50512.00381.50384.57
1-1/4″481.88512.00381.50384.83
1-1/2″572.25642.50381.50385.08
2″642.50763.00381.50445.59
2-1/2″763.00893.50381.50517.11
3″863.38893.50512.00647.62
4″1054.121024.00642.50768.64
5″1244.881275.00763.00899.65
6″1435.621405.50893.5010210.92
8″1787.001526.001024.0012712.70
10″2168.501787.001275.0015212.70
12″25410.002038.001526.0017812.70

Values from ASME B16.9-2018, Tables 6.1-7 (straight tee: C = M over the whole published range; on reducing tees M changes with the outlet, Table 6.1-8), 6.1-11 (reducers: length H depends only on the large end and is identical for concentric and eccentric) and 6.1-10 (caps: ellipsoidal shape per ASME BPVC; length E applies up to the limiting wall thickness in the last column and E1 governs for heavier wall). A reducer with a 1/2″ large end does not exist in B16.9 (the smallest tabulated combination is 3/4″ × 1/2″).

Materials: A234 WPB versus A403 WP304/WP316

RequirementASTM A234 WPB (carbon steel)ASTM A403 WP304 (stainless)ASTM A403 WP316 (Mo-bearing stainless)
Chemical composition (%, max unless range)C ≤0.30 · Mn 0.29–1.06 · P ≤0.050 · S ≤0.058 · Si ≥0.10 · Cr ≤0.40 · Mo ≤0.15 · Ni ≤0.40 · Cu ≤0.40 · V ≤0.08C ≤0.08 · Mn ≤2.00 · P ≤0.045 · S ≤0.030 · Si ≤1.00 · Cr 18.0–20.0 · Ni 8.0–11.0C ≤0.08 · Mn ≤2.00 · P ≤0.045 · S ≤0.030 · Si ≤1.00 · Cr 16.0–18.0 · Ni 10.0–14.0 · Mo 2.00–3.00
Tensile strength415–585 MPa (60–85 ksi)≥515 MPa (75 ksi)≥515 MPa (75 ksi)
Minimum yield strength240 MPa (35 ksi)205 MPa (30 ksi)205 MPa (30 ksi)
L grades (low carbon)WP304L: C ≤0.030; tensile ≥485 MPa (70 ksi), yield ≥170 MPa (25 ksi)WP316L: C ≤0.030; tensile ≥485 MPa (70 ksi), yield ≥170 MPa (25 ksi)
Construction classesMade from pipe, plate or forgings (A234)A403: class S = seamless; class W = welded with filler metal and radiography; class WX = welded with radiography of all welds; class WU = welded with ultrasonic examination (A403, para. 5.15). The certified class is stated in the lot MTC.
Fitting markingManufacturer + grade (the «WP» prefix certifies full dimensional conformance with B16.9, para. 4.4.1) + schedule or nominal wall + NPS (B16.9-2018, section 4)

Wall thickness: the pipe schedule

A B16.9 fitting has no wall of its own: it is ordered with the schedule of the pipe it will be welded to, and its nominal wall is that of the schedule per ASME B36.10M (carbon steel: sch 40, sch 80) or ASME B36.19M (stainless: sch 10S, sch 40S). The minimum wall at any point is 87.5% of nominal — the same −12.5% tolerance as pipe (B16.9-2018, Table 11-1, Note 2). The wall tables per size are published in the catalog's pipe data sheets (FT-TC-TUB-SCH40-001, FT-TC-TUB-SCH80-001 and FT-TC-TUB-INOX-001) and are not repeated here.

General specifications

ProductButt weld fittings: 90-deg long radius elbow, 45-deg elbow, straight tee, concentric and eccentric reducer and cap, in carbon steel (sch 40 and sch 80) and stainless (sch 10S and sch 40S)
Dimensional standardASME B16.9-2018 — Factory-Made Wrought Buttwelding Fittings, NPS 1/2–48 in; published catalog range 1/2–12 in
MaterialsCarbon steel: ASTM A234/A234M grade WPB. Stainless: ASTM A403/A403M grades WP304/WP304L or WP316/WP316L; the lot grade and class (S/W/WX/WU) are confirmed on quotation with its MTC
WallThat of the ordered schedule per ASME B36.10M-2022 / B36.19M-2022; minimum 87.5% of nominal (B16.9, Table 11-1, Note 2)
EndsBeveled for butt welding per ASME B16.25 (see section 4); square cut on thin wall per B16.9, Table 8-1
PressureThat of seamless pipe of equivalent material and same schedule (B16.9-2018, para. 2.1) — calculations in section 2
SaleBy the unit; 90-deg sch 40 elbow from COP $2,100 + VAT (Jul 2026); sizes in stock per figure confirmed on quotation

⚠ Important: this technical data sheet is a reference guide to the product's properties; it is not a quality certificate for the product you are buying. Heats vary from one another and may differ from the values stated here, or even depart from the standards. If your application requires compliance with a standard, always check the quality certificate (mill certificate) of the lot you are buying. If in doubt, ask one of our technical advisors →

2. Engineering basis: the B16.9 fitting is rated as pipe of its schedule

Unlike a class 150 or class 3000 threaded fitting, a butt weld fitting has no pressure class: it has a schedule. The rule is in the standard itself: ASME B16.9-2018, para. 2.1 (Basis of Ratings) establishes that the allowable pressure of fittings made to the standard may be calculated as for straight seamless pipe of equivalent material (equivalence shown by comparison of composition and mechanical properties in the respective material specifications), applying the rules of the applicable ASME B31 code, with the pipe size, wall thickness (schedule) and material marked on the fitting. Section 10 backs it by test: every fitting shall withstand without leakage the hydrostatic test pressure the piping code requires of seamless pipe of equivalent material, of the size and wall its marking identifies.

The practical consequence: the allowable pressure of every fitting in this sheet is read directly from the data sheet of the pipe of its same schedule and material, where the full Barlow calculation (formula, allowable stress S per temperature, −12.5% wall tolerance) is already published and is not duplicated here:

FittingRated asBarlow calculation published inExample at ≤38 °C
Carbon steel A234 WPB sch 40Seamless A53/A106 Gr B pipe, sch 40FT-TC-TUB-SCH40-0012″: 156 bar · 4″: 127 bar
Carbon steel A234 WPB sch 80Seamless A53/A106 Gr B pipe, sch 80FT-TC-TUB-SCH80-0012″: 221 bar · 4″: 180 bar
Stainless A403 WP304/WP316 sch 40SSeamless A312 TP304/TP316 pipe, sch 40SFT-TC-TUB-INOX-0012″ TP304: 156 bar · 2″ TP316L: 130 bar
Stainless A403 WP304/WP316 sch 10SA312 pipe, sch 10S (B36.19M wall)FT-TC-TUB-INOX-001 (same Barlow method with the 10S wall)Lower than 40S in direct proportion to its wall

The material equivalence required by para. 2.1 is met by design of the specifications: A234 WPB is made from A53/A106 Gr B type steel (240 MPa minimum yield in both) and A403 WP304/WP316 from the same analysis as A312 TP304/TP316 pipe (205 MPa minimum yield). In stainless, if the lot is class W (welded), the conservative criterion is to rate against welded A312 pipe with its joint quality factor E from ASME B31.3, Table A-1B — the full factor table is in FT-TC-TUB-INOX-001.

The three center-to-face geometric rules — and the 4″ elbow worked out

The dimensions in section 1 are not arbitrary: from NPS 1″ up they obey three exact formulas that let you check any value without the table at hand:

  1. 90-deg long radius elbow: A = 1.5 × NPS × 25.4 mm (the bend radius is 1.5 times the nominal diameter).
  2. 90-deg short radius elbow: A = 1.0 × NPS × 25.4 mm (radius = nominal diameter).
  3. 180-deg return: O = 2 × A of the matching 90-deg elbow (long or short radius).

Example — 4″ long radius 90-deg elbow: A = 1.5 × 4 × 25.4 = 152.4 mm → Table 6.1-1 publishes 152 mm (6.00 in). The 4″ short radius gives 1.0 × 4 × 25.4 = 101.6 → 102 mm, and the 4″ 180-deg LR return gives O = 2 × 152 = 305 mm (there, K = 210 mm back-to-face). The exceptions are 1/2″ and 3/4″, where the standard fixes A = 38 mm (1.50 in) — same as the 1″ elbow — instead of applying the formula; the 45-deg elbow follows no single proportional rule and is always read from the table. The full guide to 4-inch elbow dimensions and uses is in the blog article «medidas de un codo de 4 pulgadas»; this sheet contributes the complete family table and its normative basis.

3. Long radius versus short radius

The 90-deg elbow comes in two standardized radii and the difference is purely geometric — wall and material do not change:

CriterionLong radius (LR)Short radius (SR)
Bend radius1.5 × NPS (r/d = 1.5)1.0 × NPS (r/d = 1.0)
Center-to-face at 4″152 mm102 mm — takes 50 mm less per side
Resistance coefficient K (Crane TP-410, 90-deg bends, p. A-29)14 × fT20 × fT — 43% more pressure loss per elbow
Range in B16.9NPS 1/2–48 in (Table 6.1-1)NPS 1–24 in (Table 6.1-4)
UseThe default in process linesOnly where space does not allow the LR: compact racks, tie-ins against equipment, retrofits

The specification rule: long radius is the default elbow — at equal schedule it costs the same, loses less energy and softens erosion in solids-bearing fluids; short radius is reserved for real dimensional constraints and should be called out explicitly on the order ("90-deg SR elbow"), because if the order just says "90-deg butt weld elbow" every supplier ships LR. On lines with many direction changes the difference accumulates: each SR elbow adds the hydraulic equivalent of several extra diameters of straight pipe versus the LR (K = 20·fT against 14·fT per elbow, Crane TP-410).

4. End preparation: the ASME B16.25 bevel

The fitting end leaves the factory ready for the root pass: ASME B16.9-2018 (section 8 and Table 8-1) refers the bevel geometry to ASME B16.25, the buttwelding-ends standard. The preparation depends on wall thickness:

Nominal wall thickness tPreparation (B16.9-2018, Table 8-1)
Less than 5 mm (carbon steel) or 3 mm (austenitic stainless)Square cut or slight chamfer, at the manufacturer's option
From 5 mm (3 mm stainless) up to and including 22 mmPlain bevel: 37.5 deg +2.5/−0 from the perpendicular to the axis, with a 1.6 ± 0.8 mm root face — the preparation of every schedule in this sheet (the thickest catalog wall, 12″ sch 80, is 17.48 mm)
More than 22 mmCompound (double-angle) bevel per B16.25

The 37.5-deg bevel per side forms a 75-deg included V-groove with the pipe bevel; the 1.6 mm root face prevents burn-through on the root pass and, together with the root gap set by the WPS, defines full joint penetration. Transitions from the bevel to the outside surface and from the root face to the bore must lie within the maximum envelope of B16.9, Figure 8-1. Installation welding itself — process, WPS/PQR, preheat — is outside the scope of B16.9 (para. 1.7) and is governed by the line code (ASME B31.3 with qualification per ASME BPVC Section IX).

5. Manufacturing tolerances (ASME B16.9-2018, Table 11-1)

Tolerances apply to the nominal dimensions of section 1 and are what a receiving inspector checks with caliper and gage — the word commercial catalogs mention and almost never publish:

DimensionNPS 1/2″–2-1/2″NPS 3″–4″NPS 5″–8″NPS 10″–12″
Outside Ø at bevel, D+1.6 / −0.8 mm±1.6 mm+2.4 / −1.6 mm+4.0 / −3.2 mm
Inside Ø at end±0.8 mm±1.6 mm±1.6 mm±3.2 mm
Center-to-face A, B, C, M (90/45-deg LR and SR elbows, tees)±2 mm±2 mm±2 mm±2 mm
Overall length of reducers, H±2 mm±2 mm±2 mm±2 mm
Overall length of caps, E±3 mm±3 mm±6 mm±6 mm
180-deg return: center-to-center, O±6 mm±6 mm±6 mm±10 mm
180-deg return: back-to-face, K±6 mm±6 mm±6 mm±6 mm
Alignment of ends, U±1 mm±1 mm±1 mm±2 mm

ASME B16.9-2018, Table 11-1 (metric values; the standard treats the inch system as independent). Table notes: out-of-round is the sum of the absolute values of the plus and minus diameter tolerances; minimum wall at any point is 87.5% of nominal unless the purchaser specifies a different tolerance (Note 2); the angularity tolerance (off angle) is 1 mm for NPS 1/2–4 in and 2 mm for 5–8 in, with off plane of 2 and 4 mm respectively.

6. Frequently asked questions

What is the difference between a schedule 40 and a schedule 80 butt weld fitting?

Only the wall thickness — the external geometry is identical: a 2″ 90-deg LR elbow measures A = 76 mm in schedule 40 and in schedule 80 (ASME B16.9, Table 6.1-1); what changes is the wall (3.91 mm versus 5.54 mm at 2″, ASME B36.10M) and with it the allowable pressure: 156 bar versus 221 bar at ≤38 °C, read from FT-TC-TUB-SCH40-001 and FT-TC-TUB-SCH80-001. That is why the fitting is always ordered naming figure + size + schedule + material.

Does a butt weld elbow take the same pressure as the pipe?

Yes: ASME B16.9-2018 (para. 2.1) rates the fitting as straight seamless pipe of equivalent material and its same schedule, and section 10 requires it to withstand the hydrostatic test pressure the code demands of that pipe. Where design requires it, the standard allows portions of the fitting to leave the factory thicker than nominal (para. 2.2.2) — which is why an elbow weighs more than its equivalent length of pipe.

What is center-to-face and how is it measured?

It is the distance from the fitting's geometric center to the bevel face: on a 90-deg LR elbow it equals 1.5 × NPS in inches (152 mm at 4″) and is measured by resting the elbow on one face and measuring from the table to the axis of the other end. On a tee it is called C (run) and M (outlet); on a reducer the face-to-face H is used, and on a cap the length E.

When is short radius used instead of long radius?

Only when space does not allow the long radius: the SR (radius = 1.0 × NPS, from NPS 1″) saves a third of the center-to-face but loses 43% more head per elbow (K = 20·fT versus 14·fT, Crane TP-410) — detail in section 3. Long radius is the default elbow of every process line.

What do the WPB or WP304 marks stamped on the fitting mean?

They are the material grade: WPB is the ASTM A234 carbon steel and WP304/WP316 the ASTM A403 stainless grades; the «WP» prefix additionally certifies that the fitting meets all B16.9 dimensions (para. 4.4.1). The full mandatory marking is manufacturer + grade + schedule or wall + NPS (B16.9-2018, section 4): those four marks reconstruct the rating without a catalog.

Does the eccentric reducer measure the same as the concentric?

Yes: the face-to-face length H depends only on the large-end diameter and is the same for both (102 mm at 4″; ASME B16.9, Table 6.1-11). The eccentric is installed flat side up (BOP, pump suction: avoids air pockets) or down (full drainage of the run); the concentric keeps the centerline and is standard on vertical runs.

7. Application notes

Feasibility

For carbon steel process lines, the A234 WPB sch 40 fitting covers general service (127 bar calculated at 4″ and ≤38 °C, read from FT-TC-TUB-SCH40-001) and sch 80 the higher-pressure or corrosion-allowance lines (180 bar at 4″). For corrosive or sanitary fluids, the A403 WP304/WP316 family keeps the same B16.9 geometry with its grade's allowable stress (FT-TC-TUB-INOX-001); WP316, with 2–3% molybdenum, is the choice against chlorides. Stainless sch 10S is the economical wall for low-pressure conveyance where weldability, not calculation, sets the thickness. The selection rule is always the same: the fitting schedule matches the line pipe schedule — never less.

Installation

The butt joint requires aligning end to end within the U tolerance of section 5 and holding the WPS root gap; the 37.5-deg bevel and 1.6 mm root face come from the factory (B16.25) and must not be reground except for repair. Installation welding is governed by the line code — not B16.9 (para. 1.7): on process piping, ASME B31.3 with welders and procedures qualified per ASME BPVC Section IX. On stainless, argon backing purge on the root pass and later pickling/passivation of the heat-affected zone protect the passive film; do not share carbon steel tools with stainless surfaces. When mating a sch 80 fitting to sch 40 pipe, the internal offset is resolved with the B16.9 Figure 8-1 transition or by taper boring per the code.

Design

The fitting's allowable pressure is that of its schedule's pipe at design temperature: it derates with S(T) per the tables of the linked pipe data sheets (FT-TC-TUB-SCH40-001, FT-TC-TUB-SCH80-001, FT-TC-TUB-INOX-001), which include no corrosion allowance. In flexibility analysis an elbow is not straight pipe: ASME B31.3 (para. 304.2 and Appendix D) assigns it its own flexibility and stress intensification factors that depend on the radius — another point for long radius. Water hammer, sustained loads and moments belong to the project design code; on tees, the branch opening is the critical area (B16.9, para. 9.1) and the code may require reinforcement checks when combined with minimum walls.

8. Technical notice and limitation of liability

The dimensions, tolerances and rules in this sheet are nominal values from the standards cited (ASME B16.9-2018, ASME B16.25, ASTM A234/A234M, ASTM A403/A403M, ASME B36.10M/B36.19M) and the reference pressures are values calculated with the method declared in the linked pipe data sheets (Barlow per ASME B31.3). They guide selection; they are not a certificate of conformity for any given lot nor a certified product rating.

The actual behavior of each fitting depends on manufacturing — fabrication method (from pipe, plate or forgings; seamless or welded), heat treatment and actual wall within the 87.5% tolerance — and on the raw material: the grade (WPB; WP304/WP304L/WP316/WP316L) and the A403 construction class (S, W, WX, WU) are stated in the lot's mill test certificate (MTC), which TECTUL arranges upon request.

These values must not be used as the sole criterion in critical or safety applications, or wherever failure of the line may compromise people, property or the environment: in such cases the design belongs to the project's responsible engineer under the applicable code (ASME B31.1, B31.3 or the one governing the installation), with the design temperature, corrosion allowance, flexibility analysis and load cases of the actual service. Before deciding with these data, consult our technical team.

Sources

TECTUL · FT-TC-ACC-BW-001 · Rev. 001 · July 28, 2026WhatsApp +573161111666