ASTM B338 GR1 Heat Exchanger Tubes

What Is ASTM B338 GR1

ASTM B338 GR1 titanium tubes are manufactured for shell-and-tube heat exchangers, surface condensers, and evaporators. GR1 grade provides high ductility for U-bending and excellent corrosion resistance in seawater, chlorides, and chemical process media. Outside diameter range 6.35 to 76.2 mm; wall thickness 0.5 to 3.0 mm; length 1 to 30 m; seamless or welded; annealed and pickled, bright annealed, or as rolled surface.

Chemical Composition (Grade 1, Max)

Titanium 99.5% min; oxygen 0.18%; iron 0.20%; carbon 0.08%; nitrogen 0.03%; hydrogen 0.015%. Oxygen is the most critical element: lower oxygen means higher ductility for bending. GR1 has the lowest oxygen of all commercially pure titanium grades. If oxygen exceeds 0.18 percent, the material is not GR1.

Mechanical Requirements

Tensile strength 240 MPa min; yield strength (0.2% offset) 170-310 MPa; elongation 24% min in 50 mm; hardness 120-200 HV. GR1 provides the best combination of corrosion resistance and formability for heat exchanger U-bends.

Dimensional Tolerances

OD tolerance: up to 25.4 mm plus or minus 0.10 mm; 25.4-38.1 mm plus or minus 0.13 mm; 38.1-50.8 mm plus or minus 0.15 mm; 50.8-76.2 mm plus or minus 0.20 mm. Wall thickness tolerance is plus or minus 10 percent. Length tolerance: up to 6 m plus or minus 3 mm; 6-12 m plus or minus 5 mm; 12-30 m plus or minus 10 mm.

Required Tests per ASTM B338

Seamless tube requires chemical analysis, tensile test, flattening test, flaring test, and hydrostatic or eddy current test. Welded tube additionally requires the reverse flattening test and weld seam radiography when specified. Acceptance criteria include 240 MPa min tensile strength, 24% min elongation, no cracks after flattening or flaring, and leak-free hydrostatic or eddy current testing.

Common Sizes

Standard heat exchanger tube sizes include 12.70 mm OD (0.7-1.0 mm wall), 15.88 mm (0.9-1.2 mm), 19.05 mm (1.0-1.6 mm, the most common), 25.40 mm (1.2-2.1 mm), and 31.75 mm (1.2-2.5 mm). Weight per meter can be calculated as (OD mm minus wall mm) times wall mm times 0.0142 kg/m.

Seamless vs Welded

Seamless tube is pierced from a solid billet, has no weld seam, and suits high-pressure critical service. Welded tube is formed from strip and welded with full penetration, costs 15 to 25 percent less, and suits non-critical, cost-sensitive projects. For U-bend tubes with welded construction, the weld seam must be placed on the neutral axis of the bend.

U-Bending Service

Minimum bend radius is 1.5 times OD for GR1; standard bend radius is 2.0 times OD. Maximum tube OD for bending is 31.75 mm; minimum wall for bending is 0.7 mm. U-bend inspection includes dye penetrant testing on sample bends, visual inspection of all bends, and dimensional checks.

Applications

Power generation (steam turbine condensers, cooling water heat exchangers), chemical processing (shell-and-tube exchangers for acids and chlorides, evaporators), marine and offshore (seawater cooling, ballast water treatment), desalination (MSF and MED units, brine heaters), pharmaceutical (sterile cooling, clean steam condensers), and HVAC (chiller condensers).

Corrosion Resistance

Resistant to seawater and brackish water, chlorides, hypochlorite solutions, wet or dry chlorine gas, acetic acid, formic acid, dilute sulfuric acid (up to 10 percent at room temperature), nitric acid, chromic acid, and organic acids. Not resistant to hydrofluoric acid (any concentration), concentrated sulfuric acid (over 10 percent), or concentrated hydrochloric acid (over 3 percent at elevated temperature).

Frequently Asked Questions

What is the difference between B338 and B861? B338 is for heat exchanger tubes with tighter tolerances and required flattening and flaring tests; B861 is for general service seamless pipe with looser tolerances and no flattening requirement.

What is the minimum bend radius for GR1 tube? 1.5 times the outside diameter; use 2.0 times OD for standard production to reduce crack risk.

Can welded tube be used for U-bend heat exchangers? Yes, ASTM B338 allows welded tube with the weld seam placed on the neutral axis of the bend.

What tests are required for B338 GR1 tube? Seamless requires chemical, tensile, flattening, flaring, and hydrostatic or eddy current tests; welded adds reverse flattening and weld seam radiography when specified.