ASTM B167 B163 B444 UNS N06625 solution annealed Seamless Tube

1.What is Inconel 625 UNS N06625 Solution annealing Seamless Tube?

UNS N06625 (Inconel 625, W.Nr.2.4856, DIN NiCr22Mo9Nb) is a nickel-chromium-molybdenum-niobium alloy with ≥58% Ni, 20–23% Cr, 8–10% Mo, and 3.15–4.15% Nb. The alloy derives its strength from solid-solution strengthening by niobium and molybdenum in the nickel-chromium FCC matrix - no precipitation-hardening (aging) treatment is required. This distinguishes N06625 from gamma-prime strengthened grades such as N07718.

Solution annealing (also called solution treatment or anneal) heats the tube to 1093°C (2000°F) minimum, holds at temperature per thickness, and rapidly cools - typically water quench or rapid air cool. This process dissolves carbides and intermetallic phases formed during hot working or cold drawing, restores a uniform austenitic microstructure, eliminates residual forming stresses, and brings hardness to ≤20 HRC (approximately 95 HRB). The solution-annealed condition is the delivery requirement for all three ASTM standards when the tube is designated for NACE MR0175 sour service or ASME pressure code construction.

Delivering N06625 tube in the cold-drawn or cold-reduced condition without solution anneal introduces residual stress concentrations, elevated hardness above 22 HRC, and sensitized grain boundaries from carbide precipitation during cold work. These conditions can cause NACE MR0175 non-compliance, intergranular corrosion susceptibility in the heat-affected zone after welding, and stress corrosion cracking risk in chloride-containing service. Specification of "solution annealed" on the PO and verification of the heat treatment record on the MTC is mandatory for all pressure-retaining and sour-service applications.

This article provides a standard-by-standard interpretation of B167, B163, and B444 for UNS N06625 solution annealed seamless tube, covering material composition, mechanical property data, dimension and weight references, pressure-temperature ratings, equivalent grade cross-references, market price tiers, and procurement risk identification. The objective is to enable engineers and buyers to specify the correct ASTM standard on the PO, match it to design conditions and inspection requirements, and avoid the most common causes of material rejection at the project site.

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If your project drawing lists only "Inconel 625 seamless tube" without an ASTM standard number, submit the full specification sheet and process data sheet to our technical team to confirm which of B167, B163, or B444 applies before placing the order - a 15-minute verification prevents weeks of rework at incoming inspection.

2. ASTM B167 vs ASTM B163 vs ASTM B444：What is difference?

2.1 ASTM B167 - Nickel-Chromium-Iron Alloy Seamless Pipe and Tube

ASTM B167 covers seamless pipe and tube in nickel-chromium-iron alloys including UNS N06625, N06600 (Inconel 600), and N08800 (Incoloy 800). For N06625, B167 applies to general-purpose seamless pipe and tube for high-temperature structural and pressure applications. Product forms include round, oval, and rectangular cross-sections. Mandatory inspections include chemical analysis (ASTM E1479/E3047), tensile test (ASTM E8/E8M), and hydrostatic test (ASTM E1003) or nondestructive electric test per ASTM E426. Dimensional tolerances follow B167's own tolerance tables for outside diameter, wall thickness, and length.

B167 is the standard specification for process piping, furnace tubing, and structural tubing where the primary design driver is high-temperature strength and general corrosion resistance rather than heat-transfer efficiency or ultra-precise wall tolerance. A key engineering limitation: B167 does not mandate the flare (expansion) test or the eddy current test at the tighter acceptance levels required for heat exchanger tubing. Specifying B167 where a heat exchanger tube bundle is required can result in tube-to-tubesheet joint failure during expansion.

2.2 ASTM B163 - Seamless Condenser and Heat-Exchanger Tubes

ASTM B163 covers seamless condenser and heat-exchanger tubes in nickel alloys including UNS N06625. This standard is purpose-built for tube-in-shell heat exchanger, condenser, and feedwater heater applications. B163 tube is produced in smaller outside diameters (typically 6–38 mm / 1/4–1.5"), thinner walls (0.5–3.0 mm), and tighter tolerances than B167 or B444. The standard mandates eddy current testing (ASTM E426) and/or hydrostatic testing on every tube, plus a flare test (ASTM B163 Annex) and flaring test to verify ductility for tube-to-tubesheet expansion joints.

B163 tube is the correct specification for shell-and-tube heat exchanger bundles, surface condenser tubes, and feedwater heater tubes where the tube must be expanded or welded into a tubesheet. The flare test verifies that the tube end can be expanded 30% on a mandrel without circumferential cracking - a critical requirement for mechanical roll expansion joints. Engineering limitation: B163 does not address high-temperature creep-rupture properties; if the heat exchanger operates above 650°C, B444's additional high-temperature testing may be required.

2.3 ASTM B444 - Nickel-Chromium-Molybdenum-Columbium Alloy Seamless Pipe and Tube

ASTM B444 is the N06625-specific standard for seamless pipe and tube, covering two delivery conditions: Grade 1 (cold-worked, higher strength) and Grade 2 (solution-annealed, lower hardness). B444 is the standard for high-pressure, high-temperature piping in oil and gas, chemical plant, and power generation service. Mandatory inspections include chemical analysis, tensile test (ASTM E8), hardness test (ASTM E18), and hydrostatic or nondestructive electric test. B444's Grade 2 solution-annealed condition meets NACE MR0175 hardness requirement of ≤22 HRC in the as-supplied condition.

B444 is the only one of the three standards that specifically addresses N06625's two delivery conditions with distinct mechanical property requirements. For high-temperature service approaching 650°C, B444 Grade 2 is the default specification because its solution-annealed microstructure resists creep and stress-rupture. B444 does not mandate the flare test for tubesheet expansion; therefore, for heat exchanger tube bundles, B163 must be specified in addition to or instead of B444.

After reviewing the three standards, confirm which ASTM specification your project design code references - ASME B31.3 process piping typically cites B444/B167; TEMA heat exchanger specifications cite B163; ASME BPVC Section VIII may cite either B167 or B444 depending on the pressure and temperature design. Submitting the wrong standard on the PO is the single most common cause of owner rejection at final document review.

3. ASTM B167 vs ASTM B163 vs ASTM B444:Standard Comprehensive Comparison Table

For reference only, subject to final technical confirmation.

4. ASTM B167 vs ASTM B163 vs ASTM B444 Incoenl 625:Material Performance Data Tables

Chemical composition for UNS N06625 is identical across all three ASTM standards:

For reference only, subject to final technical confirmation.

Mechanical properties by delivery condition and standard:

For reference only, subject to final technical confirmation.

5. Incoenl 625 UNS N06625:Industry Application Classification

5.1 Chemical & Petrochemical Processing

N06625 seamless tube is used in reactor effluent coolers, sour gas separator internals, acid gas injection lines, and amine regenerator reboiler tubes. Service conditions: H&sub2;S partial pressure to 50 bar, CO&sub2; to 100 bar, chlorides in produced water, temperature 40–250°C. ASTM B444 Grade 2 solution-annealed is the standard specification; NACE MR0175 compliance is mandatory. For heat exchanger bundles in these units, B163 is specified to ensure flare-test-verified ductility for tubesheet expansion.

5.2 Aerospace Industry

N06625 tube is used in aircraft engine exhaust nozzles, combustor liner cooling tubes, hydraulic lines, and fuel system tubing. Service conditions: temperature to 980°C (oxidizing), pressure to 310 bar, vibration and thermal cycling. ASTM B167 is the typical specification for structural and exhaust tubing; B444 may be specified for pressure-critical lines. Tubes must meet AMS 5588 or AMS 5666 supplementary requirements in many aerospace programs, which exceed B167/B444 minimums in NDT and dimensional tolerance.

5.3 Nuclear Engineering

N06625 is qualified for nuclear steam generator tube bundles, reactor internals cooling lines, and spent fuel pool liner tubes. Service conditions: primary/secondary water chemistry at 280–325°C, neutron flux, high-purity water. B163 is the mandatory specification for steam generator tubing; supplementary requirements include grain size 5–8 per ASTM E112, full-body UT at level C sensitivity, and 100% eddy current testing. Material certification requires traceability from melt to finished tube with full N-stamp documentation per ASME Section III.

5.4 Marine & Offshore Equipment

N06625 seamless tube is used in subsea manifold jumper tubing, umbilical conduit tubes, seawater-cooled heat exchanger tubes, and offshore platform fire water system piping. Service: seawater (3.5% Cl−), H&sub2;S in produced gas, temperature 0–90°C, pressure to 690 bar for subsea. B444 Grade 2 is specified for pressure piping; B163 for seawater-cooled heat exchanger bundles. NACE MR0175 and DNV-OSS-402 compliance is typical; full PMI verification per ASTM E1621 at installation.

5.5 Heat Exchanger, Condenser & Superheater Tubing

N06625 B163 tube is specified for shell-and-tube heat exchanger bundles in FGD (flue gas desulfurization) units, surface condensers, and feedwater heaters. Service: flue gas with SO&sub2;/SO&sub3; + chlorides at 50–180°C; saturated steam at 40–60°C; feedwater at 150–300°C. B163's flare test and eddy current test at tighter acceptance levels are the reason B163 - not B167 or B444 - is the correct specification. For superheater tubing above 600°C, B444 Grade 2 may be specified in addition to B163 for the high-temperature creep resistance data.

Chemical & Petrochemical Processing

Aerospace Industry

Heat Exchanger, Condenser & Superheater Tubing

Nuclear Engineering

6. Full Parameter Reference Data Series

Dimension specification reference (common OD and wall thickness ranges by standard):

For reference only, subject to final technical confirmation.

Theoretical weight reference (selected common sizes, kg/m):

For reference only, subject to final technical confirmation. Density = 8.44 g/cm³ (UNS N06625).

Pressure rating reference (B444 Grade 2 solution annealed, selected sizes and temperatures, bar):

For reference only, subject to final technical confirmation. Calculated per ASME B31.3 with allowable stress at temperature.

Equivalent material grade cross-reference:

For reference only, subject to final technical confirmation.

Market reference price range by standard (USD/kg, FOB Chinese port):

For reference only, subject to final technical confirmation. Prices fluctuate with Ni/Mo/Nb raw material indices.

Now that all parameter tables are available, provide your project's OD, wall thickness, design temperature, pressure, and service medium to our technical team for a precise specification match and quotation - the 5-minute verification confirms whether B167, B163, or B444 applies and identifies any supplementary test requirements before material is committed.

7. Supplier Supply & Quality Control Capacity

Our N06625 seamless tube production follows the route: VIM (vacuum induction melting) + ESR (electroslag remelting) for billet, hot extrusion or pilger rolling for hollow, cold rolling or cold drawing for final dimensions, and solution annealing at 1093°C with rapid cooling. Full heat treatment records accompany every lot. Each tube is marked with heat number, standard designation (B167/B163/B444), grade, size, and supplier name per ASTM requirements.

Quality control capabilities include: chemical analysis by OES (ASTM E3047); tensile and hardness testing per ASTM E8 and E18; hydrostatic testing to 1.5× design pressure per ASTM E1003; eddy current testing per ASTM E426 at sensitivity calibrated to ASME standard notches; ultrasonic testing per ASTM E213 for long seams and laminations; PMI per ASTM E1621 for elemental verification; and grain size measurement per ASTM E112. All test reports are compiled into an EN 10204 3.1 or 3.2 MTC with full traceability from melt to finished tube.

Export packaging: each tube is individually wrapped in rust-inhibitor VCI paper, bundled in seaworthy wooden cases with steel banding, marked with heat number and size for traceability, and shipped by sea (FCL/LCL), air, or express per project urgency. Third-party inspection by SGS, BV, TÜV, DNV, or Lloyd's Register is available on request. Typical lead time: 15–25 working days for stock sizes; 25–40 working days for custom sizes and supplementary test requirements.

Request Quotation

For project-specific specification verification, submit your process data sheet, design code, and tube drawing to our metallurgical engineering team. We will confirm the ASTM standard, delivery condition, NDT requirements, NACE applicability, and supplementary test items, then provide a quotation with a full EN 10204 3.1/3.2 MTC package, third-party inspection arrangement, and export delivery schedule.

8. FAQ

Q: What is the difference between ASTM B167, B163, and B444 for Inconel 625 tube?

A: B167 covers general seamless pipe and tube for structural and pressure applications. B163 covers heat exchanger and condenser tubes with tighter tolerances, flare test, and eddy current testing. B444 is N06625-specific, defining Grade 1 (cold-worked) and Grade 2 (solution annealed) with distinct mechanical property minimums. The standards are not interchangeable; the application determines which applies.

Q: What does "solution annealed" mean for N06625 tube?

A: Solution annealing heats the tube to 1093°C minimum, holds, and rapidly cools to dissolve carbides, relieve forming stresses, and achieve hardness ≤20 HRC. This condition is mandatory for NACE MR0175 sour service and for ASME pressure code construction. B444 Grade 2 is the solution-annealed delivery condition.

Q: Can I use B444 tube for a heat exchanger bundle?

A: Not as the sole specification. B444 does not mandate the flare test required for tube-to-tubesheet mechanical expansion. For heat exchanger bundles, B163 must be specified. If the exchanger also operates above 600°C, B444 Grade 2 may be specified in addition to B163 for creep-rupture data.

Q: How do I verify NACE MR0175 compliance on the MTC?

A: The MTC must state: (1) UNS N06625, (2) delivery condition "solution annealed" or "Grade 2" per B444, (3) hardness test result ≤22 HRC per ASTM E18, and (4) heat treatment temperature and cooling method. If Grade 1 (cold-worked) is supplied, MR0175 requires lot-by-lot SSC testing per NACE TM0177 Method A.

Q: What is the maximum service temperature for N06625 tube?

A: The continuous oxidation limit is approximately 982°C. For structural load-bearing service, the recommended limit is 650°C. Above 650°C, creep-rupture data per ASTM E139 should be consulted. For ASME B31.3 design, allowable stress values are published in ASME BPVC Section II Part D for N06625 up to 816°C.

Q: Which filler metal is used for welding N06625 tube?

A: ERNiCrMo-3 (AWS A5.14) for GTAW/GMAW; ENiCrMo-3 (AWS A5.11) for SMAW. No preheat; interpass temperature below 150°C. No post-weld heat treatment is required. For dissimilar joints to carbon steel or 316L, ERNiCrMo-3 remains the preferred filler.

Before finalizing your purchase order, verify the drawing's ASTM standard number, delivery condition, NDT level, and NACE compliance against the MTC checklist above - then submit the full technical requirements, batch quantity, and project schedule to our sales team for a compliant quotation with correct standard designation on the EN 10204 3.1/3.2 certificate.