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Forged Tees & Crosses
A comprehensive engineering reference for EPC contractors, piping engineers and procurement teams — covering equal and reducing tee geometry, branch reinforcement mechanics, lateral and cross configurations, ASME B16.9 dimensional data, SIF factors for piping stress analysis, pressure design of branch connections, material grades, NACE compliance and full project documentation for all process piping branch connection applications.
Tee & Cross Types, Branch Connection
Mechanics & Reinforcement Principles
ASME B16.9 · B31.3 · Branch SIF · Crotch Thickness
Definition and Engineering Function
A butt weld tee is a pipe fitting that creates a branch connection from a main pipe run. It has three openings: two inline openings (the run or header) and one perpendicular opening (the branch). When the branch and run openings are the same size, it is an equal tee; when the branch is smaller than the run, it is a reducing tee. A cross has four openings — two inline (run) and two perpendicular (branches) at 180° to each other.
Butt weld tees per ASME B16.9 are forged or extruded fittings in which the branch opening is integrally formed into the run body during manufacture. This integral forging provides the branch reinforcement that is required by ASME B31.3 to compensate for the opening cut in the run pipe wall. In contrast, a fabricated branch connection (welded-on branch nipple or weldolet) requires separate area reinforcement calculations per ASME B31.3 Clause 304.3 — a standard B16.9 tee is pre-qualified as inherently reinforced and requires no separate area replacement calculation.
When a circular hole is cut in a cylindrical pressure vessel or pipe wall for a branch connection, the removed pipe wall material can no longer carry its share of the hoop stress. This stress must be redistributed to the material around the hole — creating a stress concentration at the branch intersection. The ratio of branch-to-run diameter (d/D) governs the severity: a large-bore branch creates a larger stress concentration than a small one. A forged tee per ASME B16.9 addresses this by providing additional wall thickness in the crotch region — the curved zone between the run and branch on the compression side of the junction — which is significantly thicker than either the run or branch pipe walls. This integral reinforcement is the manufacturing advantage of a forged tee over a fabricated branch connection.
Tee Anatomy — Four Key Dimensions
Tee and Cross Types — Engineering Descriptions
ASME B16.9 Dimensional Data,
SIF Analysis & Pressure Drop
Centre-to-End M · SIF · K-Factor · Branch Reinforcement
| NPS (Equal) | OD (mm) | Centre-to-End M, Run (mm) | Centre-to-End M, Branch (mm) | Sch STD Wall (mm) | Sch XS Wall (mm) |
|---|---|---|---|---|---|
| ½" | 21.3 | 25 | 25 | 2.77 | 3.73 |
| 1" | 33.4 | 38 | 38 | 3.38 | 4.55 |
| 1½" | 48.3 | 51 | 51 | 3.68 | 5.08 |
| 2" | 60.3 | 57 | 57 | 3.91 | 5.54 |
| 3" | 88.9 | 76 | 76 | 5.49 | 7.62 |
| 4" | 114.3 | 95 | 95 | 6.02 | 8.56 |
| 6" | 168.3 | 143 | 143 | 7.11 | 10.97 |
| 8" | 219.1 | 178 | 178 | 8.18 | 12.70 |
| 10" | 273.0 | 216 | 216 | 9.27 | 12.70 |
| 12" | 323.8 | 254 | 254 | 9.53 | 12.70 |
| 16" | 406.4 | 305 | 305 | 9.53 | 12.70 |
| 20" | 508.0 | 381 | 381 | 9.53 | 12.70 |
| 24" | 609.6 | 457 | 457 | 9.53 | 12.70 |
ASME B16.9-2018. Centre-to-End dimension M is the distance from the centreline of the fitting to the bevel end face of each opening. For equal tees, run M = branch M for the given NPS. For reducing tees, run M is the same as for the equal tee of that run NPS; branch M is based on the branch NPS from the same table. All dimensions in mm.
h = (4.4 × T_b) / D_o // h = branch wall × 4.4 / run OD (simplified per B31.3 App.D Table D300)
i_run = 0.75 × i_branch // SIF at run; always < branch SIF for tees
// WORKED EXAMPLE: NPS 6" Equal Tee, A234 WPB Sch 40 (T_b=7.11mm, D_o=168.3mm)
h = (4.4×7.11)/168.3 = 0.186
i_branch = 0.9/0.186²³ = 0.9/0.322 = 2.80 // Branch SIF = 2.80 — enters piping stress model at branch node
i_run = 0.75×2.80 = 2.10 // Run SIF = 2.10 — lower than branch; governs if run is the loaded member
| Flow Path | Fitting Type | K-Factor (Turbulent) | Equivalent Pipe Length (L/D) | Relative Pressure Drop |
|---|---|---|---|---|
| Branch to Run (90°) | Equal Tee — Standard | 1.0–1.5 | 60 | High — large flow resistance |
| Run to Run (through) | Equal Tee — Standard | 0.3–0.5 | 20 | Moderate |
| Branch to Run (45°) | Lateral Tee | 0.5–0.7 | 30 | Moderate — lower than 90° |
| Run to Run (through) | Lateral Tee | 0.2–0.3 | 14 | Low |
| Branch (any) to Run | Reducing Tee (d/D=0.75) | 0.7–1.0 | 45 | Moderate — lower than equal tee |
| Branch (any) to Run | Reducing Tee (d/D=0.5) | 0.5–0.7 | 30 | Low–Moderate |
K-factors per Crane TP-410, 2009 edition. Values are for fully turbulent flow (Re > 10,000). Actual K-factor depends on flow velocity, diameter ratio d/D for reducing tees, and branch-to-run flow ratio. For critical pressure drop calculations, use the actual velocity and friction factor with the crane method rather than tabulated K-factors alone. Lateral tees (45°) consistently deliver 30–50% lower pressure drop than 90° standard tees for the branch flow path.
Material Grades, NACE & HIC Compliance
& Forming and PWHT Requirements
NACE MR0175 · HIC TM0284 · PWHT · Charpy Impact
| Material | ASTM Grade | Yield (MPa) | Temp Range (°C) | Corrosion | Key Application |
|---|---|---|---|---|---|
| CS — Standard | A234 WPB | ≥240 | −29 to +538 | Low | Process piping, oil & gas, utilities, headers |
| CS — High Strength | A234 WPC | ≥275 | −29 to +538 | Low | High-yield piping, Class 600+ branch connections |
| LTCS −46°C | A420 WPL6 | ≥240 | −46 to +343 | Low | LNG, ethylene, cryogenic branch connections |
| LTCS −73°C | A420 WPL3 | ≥205 | −73 to +343 | Low | Deep cryogenic, ethylene/LNG plant |
| 1.25Cr-0.5Mo | A234 WP11 Cl.1 | ≥205 | −29 to +593 | Moderate | High-temp refinery headers, H₂ service |
| 2.25Cr-1Mo | A234 WP22 Cl.1 | ≥205 | −29 to +621 | Moderate | Hydrocracker, reformer branch tees |
| 9Cr-1Mo-V | A234 WP91 | ≥415 | −29 to +649 | Moderate | USC steam headers, power plant tees |
| SS 304/304L | A403 WP304/304L | ≥205 | −196 to +816 | High | Chemical, pharma, food, cryogenic headers |
| SS 316/316L | A403 WP316/316L | ≥205 | −196 to +816 | Very High | Offshore, chloride, chemical, pharma tees |
| SS 321 | A403 WP321 | ≥205 | −196 to +816 | High | High-temp SS, sensitisation resistance |
| Duplex 2205 | A815 WP-S31803 | ≥448 | −50 to +315 | Very High | Offshore sour, seawater, chloride headers |
| Super Duplex | A815 WP-S32750 | ≥550 | −50 to +300 | Extreme | Subsea, HPHT, severe sour branch tees |
| Inconel 625 | B366 WPN-06625 | ≥276 | −196 to +980 | Extreme | Corrosive acid, high-temp, offshore tees |
Manufacturing Method: Forging vs Extrusion
Butt weld tees are manufactured by two primary processes: (1) Hot extrusion (extrusion forming) — a plug or mandrel is forced radially outward through the wall of a heated pipe cylinder to form the branch opening and establish the crotch reinforcement. This process produces tees in a single operation and is the most common method for sizes up to NPS 12"; and (2) Hot press forming (die pressing) — a heated pipe section is formed in a two-part die that shapes both the run and branch simultaneously. Used for larger bore tees (NPS 12"+). Both processes create a forged (wrought) microstructure in the crotch region that is stronger than a cast or fabricated equivalent. All tees per ASME B16.9 must be made from wrought materials — cast tees are not permitted.
NACE and HIC Requirements
Tees in sour H≶S service must comply with NACE MR0175 / ISO 15156. For A234 WPB tees, maximum hardness 22 HRC (237 HB) across the full cross-section including the thickened crotch zone — the crotch must be specifically included in the hardness measurement locations because it is the thickest section and may have a different cooling rate and hardness than the run wall. For high H≶S partial pressure wet gas service, HIC-resistant base material (NACE TM0284) and HIC testing of the finished tee are required. For duplex 2205 tees, ferrite content (FN 35–65%) and hardness (≤28 HRC) must be verified at multiple locations including the crotch.
Applications, Forged Tee vs Weldolet,
& Quality Control and Documentation
Forged Tee vs Weldolet · EN 10204 3.2 · PMI · NDE
Forged Tee vs Weldolet — Engineering Selection Guide
The two principal methods for creating a branch connection in a butt weld piping system are: (1) a forged butt weld tee per ASME B16.9, which is pre-engineered and pre-qualified by the standard; and (2) a branch connection fitting (weldolet, sockolet, nipolet, latrolet) welded onto a hole cut in the run pipe wall. The selection between these options depends on the branch-to-run size ratio, the pipe class, the available space and the piping specification.
| Criterion | Forged Tee (B16.9) | Weldolet / Branch Fitting |
|---|---|---|
| Branch-to-run ratio d/D | d/D = 1.0 to 0.5 — standard | Any d/D including very small branches |
| Reinforcement calculation? | Not required — pre-qualified by B16.9 | Required per ASME B31.3 Cl.304.3 |
| Pressure rating | Same as mating pipe schedule | Per manufacturer's pressure-temperature tables |
| Welds required | 2 butt welds (run) + 1 butt weld (branch) | 1 set groove weld (outlet on run pipe) |
| NDE access | All welds accessible from outside | Fillet/partial pen weld inspection more complex |
| Fatigue performance | Excellent — smooth transition, integral body | Depends on weld quality; weld toe is crack initiation |
| Space requirement | Requires full tee face-to-face dimension | Compact — can be closer to other fittings |
| Small branches (d/D < 0.3) | Not practical — reducing tee too bulky | Weldolet preferred for small branches |
| Category M (highly toxic)? | Acceptable — full penetration BW | Check specific outlet type acceptability |
Applications by Industry
Equal and reducing tees in A234 WPB (Sch STD to Sch 80) are the dominant fitting for all process header branch connections in refinery and petrochemical plant piping — cooling water headers, fuel gas distribution manifolds, steam distribution headers, pump suction and discharge headers, heat exchanger inlet/outlet piping and column feed/product piping. A234 WP11 and WP22 for high-temperature hydrogen service branch connections; A403 WP316L for corrosive chemical service; A815 S31803 (duplex 2205) for sour service with chloride. All NACE sour service tees require hardness mapping of the crotch zone as a mandatory additional QC step not required for standard tees.
Duplex 2205 (A815 WP-S31803) and super duplex (WP-S32750) equal and reducing tees are standard for offshore platform process piping manifolds, production headers, test separator piping, gas lift systems and seawater service headers. Large-bore offshore tees (NPS 8" and above in duplex) require EN 10204 3.2 MTC with TPI countersignature, 100% PMI, NACE hardness mapping (including crotch), Charpy impact testing, ferrite content measurement (FN 35–65%), and UT/PT NDE on all welds.
A234 WP22 (2.25Cr-1Mo) and A234 WP91 (9Cr-1Mo-V) equal tees are used for main steam, hot reheat and extraction steam branch connections and header tees in power plants. WP91 tees require controlled PWHT (760–788°C) and post-PWHT hardness verification — the crotch section is the most critical zone for PWHT effectiveness and must be included in the hardness survey. Creep-fatigue is the primary long-term failure mode for power plant tees at high steam temperature — the branch SIF must be included in the piping flexibility analysis with conservative SIF values for the elevated temperature creep regime.
A420 WPL6 (impact tested at −46°C) and A420 WPL3 (−73°C) tees are specified for LNG plant process piping branch connections. Charpy V-notch impact testing at MDMT is mandatory — minimum 27 J (20 ft-lb) at test temperature. A403 WP304L tees for cryogenic liquid piping where austenitic microstructure provides inherent toughness. The crotch zone of a cryogenic tee must be included in the Charpy impact programme — it is the thickest section and the cooling rate during heat treatment may produce a different microstructure than the thinner run and branch walls.
A403 WP316L equal and reducing tees are the standard for chemical plant distribution headers — acid distribution manifolds, solvent headers, caustic distribution piping, chemical injection ring mains and pharmaceutical CIP/SIP headers. For pharmaceutical and food-grade piping, electropolished SS 316L tees with Ra ≤ 0.8 µm internal bore finish are required — the crotch internal transition must also be smooth and free of dead legs where product can accumulate and not be adequately flushed during CIP cycles. Crotch dead-leg design must be reviewed for any pharmaceutical branch tee.
Quality Control — Tee-Specific Requirements
QC for butt weld tees per ASME B16.9 covers: (1) Centre-to-end (M) dimensions — run M and branch M verified against B16.9 tables for the specified NPS and schedule; (2) OD at all three openings — run OD (×2) and branch OD verified per B36.10M; (3) Wall thickness at all bevel ends — verified to match the specified pipe schedule; (4) Crotch wall thickness — UT measurement at the crotch zone to verify adequate reinforcement per the manufacturer's design calculation; this is the most critical and unique QC point for tees; (5) Bevel geometry — per ASME B16.25 at all three openings; (6) PMI — 100% on all SS, duplex and alloy tees; (7) NDE — RT or UT of the crotch region to verify freedom from cold shuts, incomplete fusion and internal voids that can occur in the extrusion forming process.
Export Packaging
- Tees and crosses individually wrapped in VCI poly bags (CS/alloy) or clean poly bags (SS/duplex); nested in compartmented cartons for small sizes (NPS ½" to 6"); larger sizes individually crated
- All three (or four) bevel ends protected with plastic bevel protectors; bores sealed with plastic bore caps
- Each fitting tagged with: Run NPS × Branch NPS, schedule, material grade, equal/reducing designation, heat/lot number and PO reference
- MTC (EN 10204 3.1/3.2), dimensional inspection report (CTF run and branch, OD, wall at each end), crotch UT thickness report, bevel geometry, NDE reports (RT/UT/PT of crotch), PMI (alloy grades), Charpy impact (LTCS/duplex), NACE hardness including crotch (sour service), HIC report (high H₂S sour service), ferrite content (duplex), PWHT certificate (alloy steel) in waterproof sealed envelope
| # | Document | Standard / Reference | Minimum Requirement |
|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 3.1 / 3.2 | 3.2 (TPI co-signed) for offshore / NACE / alloy / safety-critical |
| 02 | Dimensional Inspection Report | ASME B16.9 | CTF M (run & branch), OD at all openings, wall at bevel ends — all mandatory |
| 03 | Crotch Wall Thickness UT Report | ASME B16.9 / project spec. | UT at crotch crown — mandatory for all tees; confirms branch reinforcement |
| 04 | Bevel End Geometry Report | ASME B16.25 | All three (or four) openings; bevel angle, land, root face confirmed |
| 05 | RT / UT Crotch NDE Report | ASME V Art.2 / Art.5 | RT or UT of crotch zone — mandatory for all high-pressure and alloy tees |
| 06 | MT / PT Surface Exam Report | ASME V Art.7 | MT for CS/alloy; PT for SS/duplex; all surfaces including crotch zone |
| 07 | PMI Report (XRF / OES) | Project specification | 100% SS, duplex, Inconel, alloy and all exotic grade tees |
| 08 | Charpy Impact Report | ASTM A370 / EN ISO 148 | Mandatory for A420 WPL6/WPL3 and duplex; crotch zone included; ≥27 J at MDMT |
| 09 | NACE Hardness Report | ASTM E10 / NACE MR0175 | CS: ≤22 HRC including crotch; duplex: ≤28 HRC; sour service mandatory |
| 10 | HIC Test Report | NACE TM0284 | Required for high H≶S partial pressure sour service tees |
| 11 | Ferrite Content Report (Duplex) | ASTM E562 / image analysis | Mandatory for duplex 2205 and super duplex; FN 35–65% including crotch |
| 12 | ISPM-15 Phytosanitary Certificate | IPPC / FAO | All wood packing for international export |
RR Hydraulics manufactures and exports butt weld tees and crosses — equal tees, reducing tees, lateral tees (45°), equal crosses and reducing crosses — per ASME B16.9 and MSS SP-75, in A234 WPB/WPC, A420 WPL6/WPL3, A234 WP11/WP22/WP91, A403 WP304L/316L/321, A815 WP-S31803/S32750 and Inconel 625. NPS ½"–48", schedules Sch 10S to XXS. EN 10204 3.1/3.2 MTC, crotch UT thickness, RT/UT crotch NDE, PMI, Charpy impact, NACE hardness (including crotch), HIC testing (TM0284), ferrite content (duplex), PWHT certificates, TPI witness by BV/DNV/Lloyds/SGS/TÜV. 48-hour express dispatch on standard in-stock sizes.