640 Stainless Steel Tube – Vacuum-Remelted 15-5PH Ultra-Tough Tubular Grade for 1310 MPa Strength with 630++ Corrosion & Flaw-Free Reliability

640 Stainless Steel Tube—marketed globally as 15-5PH or UNS S15500—is the vacuum-remelted evolution of 17-4PH that eliminates delta-ferrite stringers and inclusion clusters, producing the cleanest, toughest precipitation-hardening stainless pipe on the market. With 14–15.5 % Cr, 3.5–5.5 % Ni, 2.5–4.5 % Cu and ≤0.07 % C, 640 Stainless Steel Tube can be aged from 480 °C to 620 °C to reach 1310 MPa tensile while maintaining Charpy impact ≥ 25 J at –40 °C and corrosion resistance that equals or exceeds 630 tube in most chloride media. The grade stays magnetic, machines like 304 in the solution-annealed state, and experiences < 0.05 % dimensional growth during aging—precision seamless or welded tubes hold ±0.05 mm wall tolerance without post-grind. From aerospace hydraulic lines to sour-service downhole tubing, 640 Stainless Steel Tube gives piping designers the only PH stainless alloy that truly combines ultra-high strength, superior transverse toughness, excellent corrosion resistance and vacuum-grade cleanliness in one cost-effective tubular form.

Key Features & Benefits – Why 640 Stainless Steel Tube Outperforms 630, 316 and Martensitic Tubular Grades on Cleanliness & Critical Toughness

Vacuum Arc Remelting (VAR) = Superior Cleanliness and Inclusion Control

• VIM+VAR reduces inclusion count to < 5 ppm, raising Charpy impact to 25 J at –40 °C—double that of 630 tube in the same orientation.
• Fatigue limit 550 MPa (H900) exceeds 630 by 15 %, extending service life in rotating shafts and aircraft hydraulic circuits.

Precipitation Hardening = Customisable Ultra-High Strength

• H900 (480 °C) delivers 1310 MPa tensile / 1170 MPa yield / 40 HRC—ideal for 1 000 bar hydraulic lines and sour-service downhole tubing.
• H1150 (620 °C) still provides 1000 MPa tensile with 20 % elongation and superior stress-corrosion resistance for subsea flowlines.

Enhanced Resistance to Stress Corrosion Cracking and Pitting in Chloride Environments

• PREN ≈ 18.5 meets ASTM G48 pitting test at 30 °C; outperforms 630 and equals 316L in neutral chlorides; passes 1000 h ASTM B117 with <2 % red rust.
• NACE MR0175 approved for sour service up to H1150 condition—suitable for downhole tubing in H₂S partial pressure ≤ 10 bar at 120 °C.

High Fatigue Strength for Cyclic Loading

• Rotating-beam fatigue limit 550 MPa (H900)—double that of annealed 316; perfect for aircraft landing-gear hydraulic circuits and downhole production tubing.

Excellent Impact Toughness Even at Sub-Zero Temperatures

• Charpy V-notch ≥ 25 J at –40 °C (H1150)—triple that of standard 17-4PH, eliminating brittle fracture risk in Arctic or cryogenic service.

Good Machinability and Weldability in Solution-Annealed Condition

• Machines at 85 % of AISI B1112 baseline; solution-annealed hardness HB 270 allows high-speed trepanning before aging.
• Weldable with 15-5PH, 17-4PH or 309L fillers; no pre-heat on wall thickness < 25 mm, and aging restores full HAZ strength.

Minimal Distortion During Heat Treatment of Tube

• Aging at 480–620 °C causes < 0.05 % dimensional change—precision seamless tubes hold ±0.05 mm wall tolerance without post-aging sizing.

Magnetic Properties for NDT and Induction Heating

• Ferromagnetic structure allows eddy-current inspection and induction brazing—impossible with austenitic 304/316 tubes.

Cost-Effective & Price-Stable Tubular Solution

• Nickel content 25 % lower than 316L; precipitation hardening eliminates costly quench/temper furnaces, cutting total pipe cost 15 % versus duplex 2205.

Technical Specifications

Typical Tube Dimensions

• Seamless: OD 6–219 mm, wall 0.5–25 mm, length up to 18 m
• Welded: OD 16–610 mm, wall 0.8–12 mm, length up to 12 m

Example Pressure Rating (H900, 25 mm OD × 2 mm wall)

• Allowable stress 185 MPa → max internal pressure 185 bar at 20 °C

Standards: ASTM A213 (seamless ferritic/martensitic stainless tubes), ASTM A269/A632, AMS 5659 (bar/tube), ASME SA-213, ISO 9001, AS9100 for aerospace.

Applications and Use Cases – Proven 15-5PH Pipe Performance from Aerospace Hydraulic Lines to Sour-Service Downhole Tubing

Aerospace Hydraulic and Fuel Lines

Cold-drawn OD 12 mm × 1.5 mm 640 Stainless Steel Tube aged to H900 withstands 1 000 bar cyclic pressure; 40 HRC resists erosion while magnetic property enables eddy-current inspection.

Oil & Gas Downhole Production Tubing and Instrumentation Tubes

H1150 640 Stainless Steel Tube (OD 60 mm, wall 5 mm) resists 15 % H₂S at 120 °C while carrying 1 000 MPa tensile—allowing 30 % thinner wall than standard 17-4PH bar and eliminating costly clad layers.

Marine Propeller Shaft Liners and Control Lines

H1025 640 tube (OD 150 mm, wall 8 mm) resists seawater pitting while carrying 1 070 MPa yield—40 % higher than 316L, permitting smaller OD and lower inertia.

Nuclear Reactor Instrumentation Tubes

H950 640 seamless tube (OD 40 mm, wall 2 mm) meets nuclear cleanliness (Co < 0.05 %); low magnetic permeability (< 1.05) avoids interference with control-rod sensors.

High-Pressure Chemical/Process Injection Lines

Cold-drawn OD 6 mm × 1 mm 640 tube aged to H900 withstands 1 500 bar cyclic pressure; corrosion resistance equals 316L while strength triples, eliminating thick-wall carbon steel.

Pump Shaft Sleeves and Impeller Hubs

H1025 640 sleeve resists cavitation erosion in 3 % NaCl brine; 35 HRC hardness outperforms 316 while toughness prevents brittle fracture under torque spikes.

Precision Medical Device Tubing

Hypodermic stylets and biopsy cannula use H900 640 tube; 40 HRC provides needle sharpness while 304-level passivation meets FDA biocompatibility.

High-Strength Structural Tubing in Offshore Platforms

H1150 640 welded jacket legs carry 1 000 MPa tensile; NACE MR0175 compliance allows direct sour-service exposure, eliminating internal cladding.

Comparison with Other Grades – 640 vs 630, 631, 316, 2205 Duplex, 13-8PH Tube

Pros: 640 Stainless Steel Tube offers the best combination of ultra-high strength, excellent transverse toughness and vacuum-grade cleanliness among standard PH tube grades.
Cons: Magnetic and not suitable for non-magnetic or strong reducing-acid piping; for such cases select 316L or duplex.

Manufacturing Process and Quality Assurance

640 Stainless Steel Tube is produced via vacuum-induction melting (VIM) + vacuum-arc remelting (VAR) for aerospace cleanliness, then pierce or extrude to hollow shell. Cold-pilgering reduces OD and wall to final size, solution-annealing at 1040 °C produces soft, straight condition. Aging at 480 °C (H900) to 620 °C (H1150) precipitates nano-copper particles, raising hardness to 33–40 HRC. Finishes include pickled matte, ground OD Ra ≤ 0.4 µm and electropolished ID Ra ≤ 0.2 µm for hydraulic service. All tubes are hydrostatically tested to 1.5× design pressure, 100 % eddy-current inspected, and dimensionally checked to ASTM A213/A269. Certifications include ASTM A564/AMS 5659, ISO 9001 and optional AS/EN 9100; tests include ICP chemistry, tensile at room and elevated temperature, Charpy impact, ASTM G48 pitting corrosion, ultrasonic wall thickness and grain size. Third-party inspection certificates accompany each shipment for direct aerospace PPAP submission.

Maintenance and Care Tips for 640 Stainless Steel Tube

Clean tube interiors with warm water and neutral detergent; avoid chloride bleach. For marine service, periodic fresh-water flushing removes salt deposits. Passivate in 2 % citric acid after machining to dissolve free iron. Do not expose aged (H900) sections to >425 °C for prolonged periods to avoid over-aging. Store pipe horizontally on plastic-covered racks to prevent carbon-steel contamination.

Frequently Asked Questions on 640 Stainless Steel Tube

Q: What are the advantages of VAR processing in 640 Stainless Steel Tube?
A: VAR reduces inclusions to <5 ppm, doubling transverse toughness and fatigue life versus standard 17-4PH while matching strength and corrosion resistance.

Q: Which aging condition is best for high-strength vs. corrosion balance?
A: H900 (480 °C) for max strength 1310 MPa; H1025 (550 °C) for balance; H1150 (620 °C) for max toughness and NACE sour-service compliance.

Q: Is 640 Stainless Steel Tube NACE-compliant for sour service?
A: Yes—H1150 condition is NACE MR0175 approved for H₂S partial pressure ≤ 10 bar at 120 °C, outperforming 420 and standard 17-4PH pipe.

Q: What post-weld heat treatment is required for welded tubes?
A: None—weld in solution-annealed condition, then age the entire assembly; no pre-heat or post-weld anneal needed.

Ready to combine 1310 MPa strength with vacuum-clean toughness and 304-class corrosion in one seamless or welded tube? Contact us today for custom 640 Stainless Steel Tube quotes, mill test certificates and global delivery—full metallurgical support included.