ASME B16.50-2018 — Wrought Copper and Copper Alloy Braze-Joint Pressure Fittings

🧯 ASME B16.50-2018 covers pressure-temperature ratings, materials, dimensions (laying lengths), tube stops, threaded ends, inspection tolerances, and testing for wrought copper and copper alloy braze-joint pressure fittings. Brazing operates at temperatures above soldering but below fusion welding, giving joints intermediate strength and temperature capability. These fittings are widely used in refrigeration and air conditioning, marine piping, fire protection, compressed air, and hot-water and oil circuits where leak-tight copper connections are critical. The 2018 edition revises the 2013 edition, mainly updating references and refining inspection content.

1. Scope and General Requirements 📌

Clause 1 defines the scope: pressure fittings of wrought copper and copper alloy with socket-type braze joints or dual ports. Principal types include:

• Elbows: 45° and 90° standard angles;
• Tees and crosses: straight and reducing;
• Caps and plugs: end closure;
• Couplings and reducers: straight connection and size change;
• Flanges, unions, and other special forms.

Clause 2 (General) states material and workmanship requirements; Clause 3 gives pressure-temperature ratings; Clause 4 continues the scope covering the nominal size series; Clause 5 requires marking. The fittings are intended for brazing, with socket depth and joint clearance assured by the dimensional tables.

2. Pressure-Temperature Ratings 🔥

Clause 3 establishes the rating tables. Ratings depend on material (annealed wrought copper or alloy), fitting type, and temperature — allowable pressure falls as temperature rises. Ratings coordinate with the corresponding copper tube (e.g., ASTM B88) so that matched tube-and-fitting systems are consistent. Nonmandatory Appendix A gives the rating derivation method and Appendix B describes the quality system program.

3. Dimensions, Laying Lengths, and Tube Stops 📏

Clause 7, “Laying Lengths,” sets end-to-end or end-to-center dimensions — the basis of braze-joint interchangeability. Clause 8, “Tube Stops,” defines the internal stop position: the tube is inserted until it bottoms on the stop, guaranteeing correct insertion depth, uniform filler clearance, and consistent joints. Clause 9, “Inspection Tolerance,” gives allowable deviations for socket inside diameter, outside diameter, and length. Clause 12, “Gaging,” requires standard gages to verify socket dimensions and maintain the specified brazing clearance.

4. Materials, Marking, and Threaded Ends 🔧

Clause 6 specifies materials: wrought copper or compliant copper alloys with adequate strength, ductility, and corrosion resistance, annealed so that brazing preserves properties. Clause 10, “Threaded Ends,” covers thread size and machining (e.g., NPT pipe threads) for fittings with threaded ends; combination braze/thread fittings must meet tolerances at both ends. Clause 5 marking requires the manufacturer’s name or trademark and size for traceability and correct selection.

5. Engineering Practice Essentials 🛠️

• 🔍 Selection: read B16.50 ratings against system design pressure and temperature; confirm brazing suits high-pressure refrigeration or oil circuits;
• 🔧 Brazing practice: clean the tube OD and socket ID, apply flux where required (copper-phosphorus filler is self-fluxing on copper-to-copper), heat with oxy-acetylene or propane until filler melts and penetrates, then cool undisturbed;
• 📋 Inspection: after brazing check fillet uniformity, porosity, and penetration; pressure or hydrotest where specified;
• 🔄 Health and safety: use lead-free filler for potable water per local codes; ventilate and take fire precautions during brazing.

6. Frequently Asked Questions ❓