What Is B-2 Pipe?
B-2 is a solid-solution strengthened nickel-molybdenum alloy, designated UNS N10665, with molybdenum as the principal alloying element at 26.0–30.0 %. That high molybdenum level is what gives the alloy its exceptional resistance to hydrochloric acid at all concentrations and temperatures, as well as to sulfuric acid, acetic acid and phosphoric acid under reducing conditions.
Because carbon and silicon are held to very low levels, B-2 pipe resists the formation of grain-boundary carbide precipitates in the weld heat-affected zone, so the corrosion resistance of the joint matches the parent metal. The alloy is supplied as seamless pipe under ASTM B622 / ASME SB622, with welded pipe and tube available under ASTM B619 and B626.
One design limitation must be respected: B-2 is intended for reducing environments. It should not be used in oxidizing media or in streams that contain oxidizing salts, because those conditions rapidly degrade the protective surface film.
Chemical Composition of B-2 Pipe (UNS N10665)
| Element | Composition, % | Element | Composition, % |
|---|---|---|---|
| Ni | Remainder | Mo | 26.0–30.0 |
| Fe | 2.0 max | Cr | 1.0 max |
| Mn | 1.0 max | Co | 1.0 max |
| Si | 0.1 max | C | 0.02 max |
| P | 0.04 max | S | 0.03 max |
Mechanical and Physical Properties
| Property | Value | Condition |
|---|---|---|
| Tensile strength | 110 ksi (approx. 760 MPa) | Solution annealed pipe |
| 0.2 % yield strength | 51 ksi (approx. 350 MPa) | Solution annealed pipe |
| Elongation | 40 % | 2 in / 50 mm gauge |
| Physical property | Value | Temperature |
|---|---|---|
| Density | 9.22 g/cm³ | 22 °C |
| Specific heat | 0.089 kcal/kg·°C | Room temperature |
| Melting range | 1370–1418 °C | – |
| Modulus of elasticity | 217 kN/mm² | Room temperature |
| Electrical resistivity | 137 µΩ·cm | 0 °C |
| Coefficient of expansion | 10.3 µm/m·°C | 20–93 °C |
| Thermal conductivity | 11.1 W/m·K | 0 °C |
Pipe Size Range and Supply Options
Round pipe: outside diameter 4 mm to 200 mm.
Square tube: 10 × 10 mm to 100 × 100 mm.
Rectangular tube: 10 × 20 mm to 50 × 100 mm.
Wall thickness: 0.6 mm to 6.0 mm, with heavier schedules on request.
Length: 1 to 6 m random or fixed lengths, cut to drawing.
Surface: black, bright polished, rough turned, matte, No.4 or BA finish.
Production route: hot rolled or cold rolled, seamless or welded and drawn.
Order standards: ASTM / ASME, JIS, GB and DIN / EN equivalents, with ISO, SGS or BV inspection certificates.
Applications of B-2 Nickel-Molybdenum Pipe
Hydrochloric acid production, storage and transfer lines at every concentration.
Sulfuric acid and phosphoric acid process piping in reducing duty.
Acetic acid and organic acid plants, including esterification circuits.
Chemical process equipment such as reactors, columns, reboilers and condensers.
Vacuum furnace internals and mechanical parts used in reduced-pressure environments.
Pickling line piping, heat exchangers and SO₂ handling equipment where chlorides are absent.
Fabrication, Welding and Heat Treatment
B-2 pipe is machined with carbide tooling at reduced surface speed because the alloy work hardens quickly. Cold bending and flaring are performed in the solution-annealed condition. Welding is carried out with matching nickel-molybdenum filler metal, low heat input and a controlled interpass temperature; the joint area must be cleaned free of oxide, grease and embedded iron before welding because contamination is the main cause of premature corrosion. Hot forming takes place between about 1065 °C and 1175 °C, after which the pipe is solution annealed at approximately 1065 – 1150 °C and water quenched. The alloy must not be exposed to oxidizing or nitrate-bearing media during pickling or service.
Frequently Asked Questions
Q: What is the UNS number for B-2 pipe?
B-2 nickel-molybdenum pipe is designated UNS N10665 and is ordered to ASTM B622 for the seamless product or ASTM B619 and B626 for welded pipe and tube.
Q: Which acids is B-2 pipe suitable for?
It is designed for reducing acids, especially hydrochloric acid at all concentrations and temperatures, plus sulfuric, acetic and phosphoric acid streams free of oxidizing agents.
Q: Can B-2 pipe be used in oxidizing conditions?
No. Oxidizing media, oxidizing salts and aerated chloride streams attack the alloy quickly, so a nickel-chromium-molybdenum grade should be substituted in those duties.
Q: Why does B-2 resist weld decay?
Carbon and silicon are kept at very low levels, which prevents continuous grain-boundary carbide precipitation in the heat-affected zone and preserves intergranular corrosion resistance.
Q: What sizes of B-2 pipe can be produced?
Round pipe from 4 mm to 200 mm outside diameter, square tube from 10 × 10 mm to 100 × 100 mm and rectangular tube from 10 × 20 mm to 50 × 100 mm.
Q: What is the maximum service temperature for B-2 pipe?
The alloy holds useful strength to about 700 °C, but it must be protected from oxidizing species throughout the operating range and during any thermal treatment.
