ASTM B163 Nickel Alloy Condenser & Heat Exchanger Tube Standard

What is ASTM B163?

ASTM B163 is the Standard Specification for Seamless Nickel and Nickel Alloy Condenser and Heat-Exchanger Tubes. The specification is published by ASTM International, a globally recognised organisation that develops technical standards for materials, products, systems, and services. It falls under ASTM Committee B02 on Nonferrous Metals and Alloys and is maintained by Subcommittee B02.07 on Refined Nickel and Cobalt and Their Alloys. The specification also references ASTM B829, which outlines general requirements for nickel and nickel alloy seamless pipe and tube, including testing, inspection, certification, marking, and packaging requirements.

What makes B163 different from other nickel alloy tube specs like B161, B167, or B444? B163 is application-specific. It is written for tubes that will be rolled, expanded, or bent into tubesheets and U-bends inside heat exchangers and condensers. That application focus drives 3 requirements you will not find in general-service tube specifications:

• 1. Minimum bend radius tables that vary by alloy, tube OD, wall thickness, and temper condition.
• 2. Expansion and flare testing to verify that every tube end can be rolled into a tubesheet without splitting.
• 3. Higher yield strength tubes (for Inconel 600 and Incoloy 800 families) with controlled yield ranges for specific high-pressure condenser designs.

B163 tubes are dimensioned by OD and wall thickness (average or minimum). We supply these tubes in sizes from OD 6–457 mm, wall 1–65 mm, and lengths up to 22 metres.

Minimum Bend Radius for U-Tube Fabrication

This is the section that sets B163 apart. Table 5 of the specification defines the tightest bend radius permitted for U-tube fabrication, based on tube OD, average wall, alloy family, and temper condition. Going below these limits risks cracking on the extrados (outer bend) or buckling on the intrados (inner bend).

Annealed tubes allow tighter bends than stress-relieved tubes. For example, an annealed tube up to 1/2 in. (12.7 mm) OD with a wall of 0.046–0.057 in. (1.17–1.45 mm) has a minimum bend radius of 1-3/16 in. (30.2 mm) in the annealed condition, versus 1-1/4 in. (31.8 mm) in the stress-relieved condition.

Note: These radii apply to all alloys except N08810, N08801, and N08811. For minimum-wall tubes, calculate the corresponding average wall from the tolerance table, then use Table 5. The bend radius is measured to the tube centreline.

Heat Treatment for ASTM B163 Tubes

Heat treatment requirements vary by alloy. Pure nickel and Monel 400 tubes are annealed at lower temperatures (1300–1600°F / 700–870°C for nickel, 1300–1700°F / 700–925°C for Monel) in protective atmospheres. Inconel 600 and the Incoloy 800 family require higher anneal temperatures.

For Incoloy 800H (N08810) and 800HT (N08811), the anneal must produce an ASTM grain size of No. 5 or coarser. This controlled grain growth is not a defect—it is the mechanism that gives these tubes their creep-rupture strength above 1100°F (593°C). Finer grains would sacrifice long-term strength at elevated temperatures.

Stress-relieved tubes retain residual cold-work strength. The stress-relief temperature (typically 525–900°F / 275–480°C for nickel) removes residual stresses without fully recrystallising the grain structure. B163 requires that for stress-relieved tubes with annealed ends, the tension test specimen be taken from the stress-relieved portion—not the annealed end.

Testing and Inspection Requirements

B163 testing goes beyond what general-service tube specs demand. In addition to the standard tension and hydrostatic tests, B163 adds flare testing on every random length—a requirement that directly validates whether the tube can survive being rolled into a tubesheet.

Tension Test

One specimen per lot, tested in the longitudinal direction. Full-section tubular specimens are preferred. When the tube is too large for the testing machine, longitudinal strip specimens are used. Yield strength is measured at 0.2% offset.

Flare Test

One end of each random-length tube is flared over a tapered mandrel. The expanded end must increase in OD without showing cracks, splits, or other visible defects. This test simulates the stress that occurs when tube ends are rolled into tubesheet holes. No other nickel alloy pipe or tube specification (B161, B165, B167, B444) requires this test as a standard—it is unique to B163.

Hydrostatic or NDE Test

Every tube must pass either a hydrostatic test or eddy-current testing per ASTM E571. For hydrostatic testing, the test pressure follows P = 2St/D (where S is the allowable fibre stress per B829). Tubes showing leaks are rejected. When NDE is used, the calibration reference uses a drilled hole no larger than 0.031 in. (0.79 mm).

Hardness Test (Stress-Relieved Tubes with Annealed Ends)

For stress-relieved tubes furnished with annealed ends, a Rockwell hardness test is performed on the inside surface of the tube near one end. This checks that the stress-relieved zone has maintained its target hardness and that the annealing of the ends did not extend into the body of the tube.