How to read nickel alloy fitting markings (ASTM B366, ASME B16.9, MSS SP-25)
Decode the markings on nickel alloy butt weld fittings and flanges: manufacturer symbol, grade, schedule, size, heat number and standard, with worked examples and the mistakes to avoid on receipt.
ASME B16.9 requires factory-made wrought fittings to be marked with manufacturer name or trademark, material identification, wall thickness designation or schedule number, size and - for corrosion resistant alloy fittings - the applicable specification. MSS SP-25 sets out the conventional format used across valves, flanges, fittings and unions. In practice, nickel alloy fittings also carry the heat number because that is the only link back to the mill certificate.
Anatomy of a compliant fitting marking
Element
Example
What it tells you
Manufacturer symbol
HANGO or agreed code
Who is accountable
Material grade
WP625 Gr.2 or UNS N06625
Chemistry and condition
Wall designation
SCH 40S or SCH 80S
Pressure capability after corrosion allowance
Nominal size
6" / DN150
Mating pipe size
Specification
ASTM B366
Material standard the analysis meets
Heat number
H-24481
Links to ladle analysis and mechanical tests
A worked example
Consider a marking that reads: HANGO WP625-2 B366 SCH 40S DN150 H-24481. Reading from left to right, this is a fitting manufactured by Hangbo, made from ASTM B366 WP625 in Grade 2 condition, to Schedule 40S wall thickness for DN150 pipe, traceable to heat number 24481. The certificate for that heat must show a nickel content of at least 58 %, chromium 20-23 %, molybdenum 8-10 %, niobium 3.15-4.15 %, plus tensile strength of at least 827 MPa and yield of at least 414 MPa in the annealed condition.
Warning Steel stamp dies can act as stress raisers and can also introduce iron contamination on stainless and nickel surfaces. Where the specification forbids stamping, use low stress stamps on the low stress area, vibro-etching or durable labelling, and always keep the heat number readable.
Flange markings follow ASME B16.5
Forged flanges are marked to ASME B16.5 and MSS SP-25 with manufacturer symbol, ASTM material designation, class, size, boring schedule where relevant and facing type. A typical reading is HANGO B564 N06625 CL300 DN150 SCH40S RF H-24481, which identifies an ASTM B564 Inconel 625 flange, Class 300, DN150, Schedule 40S bore, raised face, heat 24481.
Receipt checklist before you accept a delivery
Compare the marking on every fitting against the certificate heat list - no match, no acceptance.
Verify marking method does not breach specification restrictions on hard stamping.
Confirm the schedule or wall designation matches the line class; a Schedule 10S fitting in a Schedule 40S line is a common and dangerous substitution.
Run PMI on a defined sample and compare against the ladle analysis for key elements such as molybdenum and niobium, which counterfeit or mixed stock frequently fails.
Check dimensional tolerance against ASME B16.9, particularly outside diameter at the bevel and squareness of the ends.
Confirm the EN 10204 3.1 certificate and any ordered SGS third party test report are present, and that heat treatment records are included.
Keeping the chain intact through fabrication
Traceability is usually lost not at the mill but in the fabrication shop. Require your fabricator to maintain a heat map of the spool drawings, transfer heat numbers onto cut pieces before they are separated from the parent length, and keep photographic records before insulation is applied. Hangbo supplies barcoded tags on request, which makes this step straightforward.
Questions about this topic
Is the heat number always on the fitting itself?
On nickel alloy fittings it should be. Where size or specification prevents direct marking, the number must appear on a securely attached tag and be cross-referenced on the packing list and certificate.
What does the 'W' prefix mean in WP625?
In ASME usage W denotes wrought. 'WP' is the wrought product grade designation used in fitting specifications such as ASTM A403 for stainless, ASTM B366 for nickel alloys and ASTM B363 for titanium.
Can I repaint over the marking?
Only after recording it. Photograph every fitting marking before coating and store the images with the certificate package so the number survives paint, insulation and years of service.
How does this differ for titanium fittings?
The structure is identical, using ASTM B363 with WPT2 or WPT5 grade designations. Titanium markings need low chloride marking inks and stamps because some marking materials can contaminate the surface and cause embrittlement during service.
What should I do if a fitting arrives unmarked?
Quarantine it. Unmarked items cannot be certified into coded piping and most project specifications require removal from site. Ask the supplier for a documented identification procedure or replacement material.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email [email protected] or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
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Written by Hangbo Alloy Technical Team
Metallurgy & materials engineering. Reviewed against the latest ASTM, ASME and AMS specifications held on file at Hangbo Alloy. Last updated 2026-09-18.
Send us your drawing, material specification and quantity. You receive a formal quotation within 24 hours, including melting route, heat treatment, testing scope and certificate format.
