Inconel 625 seamless pipe (UNS N06625) is a nickel-chromium-molybdenum-columbium alloy pipe and tube produced to ASME SB-444. It combines 21.5% chromium, roughly 9% molybdenum and niobium stabilisation in a nickel matrix, which gives it a very broad resistance envelope: strong against chloride pitting and crevice corrosion, strong against sour service, and stable at cryogenic temperature. It is the workhorse alloy for offshore topside piping, subsea connectors, chemical injection lines and seawater systems.
Specification and Designation
| Designation | Value |
|---|---|
| UNS number | N06625 |
| ASME specification | SB-444 |
| ASTM equivalent | B444 (seamless pipe and tube) |
| Material class | Nickel-chromium-molybdenum-columbium alloy |
| Available grades | Grade 1 (annealed) / Grade 2 (solution annealed) |
Chemical Composition (ASME SB-444, Table 2)
| Element | Composition, % | Element | Composition, % |
|---|---|---|---|
| Nickel | Remainder | Carbon | 0.10 max |
| Chromium | 21.5 min | Manganese | 0.50 max |
| Molybdenum | 8.0 min | Silicon | 0.50 max |
| Niobium (Cb) | 3.15 min – 4.15 max | Phosphorus | 0.015 max |
| Iron | 5.0 max | Sulfur | 0.015 max |
| Aluminium | 0.40 max | Cobalt (if determined) | 1.0 max |
Limits quoted directly from ASME BPVC Section II Part B, SB-444 Table 2. Note that chromium and molybdenum carry a minimum only, with no upper bound specified.
Mechanical Properties by Grade
| Condition | Tensile, min ksi (MPa) | Yield (0.2%), min ksi (MPa) | Elongation, min % |
|---|---|---|---|
| Grade 1, annealed | 120 (827) | 60 (414) | 30 |
| Grade 2, solution annealed | 100 (690) | 40 (276) | 30 |
From ASME SB-444 Table 1. Grade 1 is annealed at 871°C minimum; Grade 2 is solution annealed at 1093°C minimum, optionally followed by a stabilisation anneal at 982°C minimum to improve resistance to sensitisation. Minimum strength values apply only to tubing in straight lengths.
Why 625 and not 316L or 904L
- PREN in the low 50s. 625 gives roughly 51–55 PREN against about 24 for 316L and about 34 for 904L. In chloride-bearing seawater service that gap is the difference between a service life measured in years and a service life measured in months.
- Resistance to sour oil and gas. With 9% molybdenum and niobium stabilisation, 625 performs well in H2S environments where 316L and evenDuplex 2205 are unsuitable.
- No post-weld heat treatment required for most grades. Niobium stabilisation keeps sensitisation in check, so weld joints do not need solution annealing for common service.
- Cryogenic toughness. Face-centred cubic nickel base retains impact energy down to liquid helium temperatures.
Supply Range
| Parameter | Range |
|---|---|
| Outer diameter | 6 mm – 610 mm (1/4″ – 24″) |
| Wall thickness | 0.5 mm – 60 mm |
| Length | Random length, or cut to customer requirement |
| Condition | Grade 1 annealed, Grade 2 solution annealed |
Testing and Inspection
- EN 10204 3.1 mill test certificate, third-party inspection available on request
- Hydrostatic or eddy-current testing on every tube; ASTM A999 / A1026 as applicable
- Full chemical analysis by XRF or OES, with the certificate showing the actual heat values
- Intergranular corrosion testing to ASTM G28 available on request
- Dye penetrant inspection on all pipe, ultrasonic testing on heavy wall and forgings
Surface, Marking and Packing
Seamless pipe is supplied with a pickled or bright annealed surface, capped at both ends and individually sleeved. Each pipe carries heat number, grade, standard, size and our works mark. Export packing is wooden cases or steel pallets with plastic end caps; plastic end caps can be replaced on request.
Applications
- Offshore and subsea production piping, risers and flowline connectors
- Seawater lift and firewater systems
- Chemical injection and hydraulic lines
- Sour gas gathering and processing equipment
- Spray nozzles, flexible tubing and downhole components
- Aerospace and cryogenic ground equipment
Related Products
For comparison, see our Inconel 600 seamless pipe for oxidising and caustic service, and our Hastelloy C-276 seamless pipe where the service is strongly oxidising acid. For the matching buttweld fittings and flanges in the same alloy, see the flange range.
Technical Enquiries
Send the specification, grade, dimensions, quantity and any third-party inspection requirement to our technical sales desk. We will confirm dimensional tolerance, delivery condition and the exact ASTM or EN standard line item, and quote FOB Shanghai or Ningbo.
Frequently Asked Questions
What is the difference between Grade 1 and Grade 2 Inconel 625?
Grade 1 is annealed at 871°C or above and meets the higher strength limits (120 ksi tensile, 60 ksi yield). Grade 2 is solution annealed at 1093°C or above and meets the lower limits (100 ksi tensile, 40 ksi yield). Grade 2 is chosen where maximum intergranular corrosion resistance is the priority; Grade 1 where higher strength is needed.
Is Inconel 625 weldable without post-weld heat treatment?
Yes for most service. Niobium stabilisation ties up carbon as NbC rather than chromium carbide, which greatly reduces sensitisation. For high-temperature or strongly oxidising service, or where the purchaser specifies it, an anneal can be included.
What does PREN mean and why does it matter?
PREN, the pitting resistance equivalent number, is a weighted sum of chromium, molybdenum, nitrogen and tungsten. It is a screening index, not a substitute for testing, but it correlates well with pitting resistance in chloride solutions and is the standard quick way to rank alloys for seawater service.
Can you supply Inconel 625 to EN 10204 3.1 with third-party inspection?
Yes. We supply 3.1 certificates as standard and can arrange Lloyd’s, BV, DNV, SGS or TUV inspection, with the inspection release applied before shipment.
What is the maximum size you can supply?
Standard seamless supply runs to 610 mm OD. For larger diameters we can offer welded construction to the same alloy and grade, or machined bar and forging stock; tell us the size and we will confirm the route.
