Bright Annealed Seamless Nickel Alloy Tube with High Nickel Content for Corrosion Resistant Heat Exchangers

ASTM B167 UNS N06600 seamless tube is a nickel-chromium-iron alloy tube intended for corrosion-resistant and heat-resistant service. Its minimum nickel content of 72% provides resistance to chloride-ion stress-corrosion cracking, while 14.0-17.0% chromium supports oxidation resistance in elevated-temperature environments.

For heat-exchanger construction, the tube can be supplied in a cold-worked and annealed condition with a bright, smooth surface suitable for tube expansion, bending, welding, and assembly into tube bundles. ASTM B167 covers seamless nickel-alloy pipe and tube, while dimensional tolerances and general requirements are controlled through ASTM B829.

ASTM B167 requires the finished material to be uniform in quality and condition, smooth, commercially straight and free from harmful imperfections. Each tube must receive either hydrostatic testing or nondestructive electric testing unless otherwise specified in the purchase order.

UNS N06600 contains at least 72.0% nickel. The high nickel level provides strong resistance to chloride-ion stress-corrosion cracking and contributes to reliable performance in many alkaline and reducing environments.

The alloy contains 14.0-17.0% chromium. Chromium forms a protective oxide film that improves resistance to oxidation and many high-temperature atmospheres.

For cold-worked and annealed tube with an outside diameter of 127 mm or less, ASTM B167 specifies:

• Minimum tensile strength: 550 MPa
• Minimum 0.2% yield strength: 240 MPa
• Minimum elongation: 30%

These minimum values provide sufficient ductility for bending, tube expansion and tube-to-tubesheet assembly.

UNS N06600 is widely selected where both corrosion resistance and elevated-temperature strength are required. Manufacturer technical data describe the alloy as suitable for applications requiring resistance to corrosion and heat, including furnace components, chemical-processing equipment and heat-treatment equipment. Actual design temperature must be determined from pressure, wall thickness, environment and applicable design code.

Bright annealing is performed in a controlled protective atmosphere to limit surface oxidation. The process produces a clean internal and external surface that reduces additional descaling and supports inspection, fabrication and welding.

A common procurement concern is whether the tube outside diameter and wall thickness are sufficiently consistent for tubesheet expansion and bundle assembly.

Production control can include:

• Continuous OD and wall-thickness monitoring
• Full-length eddy-current testing
• End-area dimensional inspection
• Ovality measurement
• Fixed-length cutting
• Customer-specific tolerance control

Inspection reports can identify actual OD, wall thickness, ovality and length rather than stating only nominal dimensions.

Purchasers frequently require confirmation that bright-annealed tube is free from heavy oxide scale, embedded iron contamination, lubricant residue and surface defects.

The supply procedure can therefore include:

• Controlled-atmosphere annealing
• Surface cleaning after forming
• Visual inspection under controlled lighting
• Internal-surface inspection
• Roughness measurement when specified
• Protective end caps and moisture-resistant packaging

Bright annealing should be treated as a controlled manufacturing condition, not merely a cosmetic finish.

Nickel-alloy substitutions can create serious service risks. Each production batch should therefore remain traceable from raw material to final shipment.

Available quality controls include:

• Heat-number traceability
• Positive material identification
• Ladle and product chemical analysis
• Mechanical testing
• Hydrostatic or eddy-current testing
• EN 10204 3.1 certification
• Third-party inspection
• Marking of grade, size, heat number and standard

ASTM B167 requires the order to identify the alloy, specification edition, condition, finish, dimensions, test method and certification requirements.

The purchase order should identify the exact standard edition because alloy coverage, referenced standards and supplementary requirements can change between revisions. ASTM B167-23 includes UNS N06600 and other nickel-chromium alloys for seamless corrosion-resistant and heat-resistant pipe and tube.

UNS N06600 seamless tubes can be installed as the heat-transfer tubes inside a shell-and-tube heat exchanger used to heat or cool corrosive process fluids.

For this application, procurement requirements normally include:

• Controlled outside diameter for accurate tubesheet-hole clearance
• Stable wall thickness for pressure design
• Bright or clean annealed surface
• Full-length nondestructive electric testing
• Bendability for U-tube configurations
• Heat-number traceability
• Tube-end cleanliness for orbital welding or expansion
• Hydrostatic testing when specified

Final material selection must consider the process-fluid composition, operating temperature, chloride concentration, pressure, flow velocity and cleaning method.