Technical knowledge
ASTM B366 explained: the specification behind nickel alloy fittings
What ASTM B366 covers, how wrought fittings differ from forged ones, the WP and CR class designations, and the dimensional and marking standards that must accompany it.
Scope and the class designations
B366 uses a WP prefix followed by a composition class number that maps to a UNS alloy. For example WP625 corresponds to N06625 and WP20CB corresponds to N08020. The class system predates the widespread use of UNS numbers, which is why purchase orders should always state both the WP class and the UNS number.
| Class | UNS | Common name |
|---|---|---|
| WP625 | N06625 | Inconel 625 |
| WP825 | N08825 | Incoloy 825 |
| WP276 | N10276 | Hastelloy C-276 |
| WP400 | N04400 | Monel 400 |
| WP600 | N06600 | Inconel 600 |
Seamless and welded construction
B366 permits both seamless and welded construction, and the distinction must be stated. Seamless fittings are formed from tube or pipe and have no longitudinal seam, which is preferred for high pressure and for corrosive service where a seam could be a preferential attack path. Welded fittings are formed from plate or strip and are widely accepted, but they require the weld to be examined and, where required, radiographed.
Companion standards you must also name
- ASME B16.9 for butt weld fitting dimensions including centre to end dimensions and tolerances.
- ASME B16.25 for the weld end bevel preparation.
- MSS SP-25 for marking.
- ASME B16.11 only if the project includes forged fittings of different type, which is a separate specification from B366.
Testing and documentation
Order the heat treatment condition explicitly, usually solution annealed and pickled. Specify dimensional verification against ASME B16.9, positive material identification coverage, dye penetrant examination where required, and a mill test certificate to EN 10204 3.1. Where the project requires independent verification, documented testing by SGS can be arranged and the third party test report issued with the shipment.
Questions about this topic
Is ASTM B366 the same as ASME B16.9?
No. B366 is the material specification and B16.9 is the dimensional standard. A complete fitting order names both, plus the welding end preparation standard ASME B16.25.
Are welded B366 fittings acceptable?
Yes, and they are widely used. The weld must be made with a qualified procedure, examined, and where specified radiographed. State whether seamless or welded construction is required on the order.
What does the WP prefix mean?
It identifies a wrought product class in the B366 composition tables. Because the class numbering is older than the UNS system, always state both the class and the UNS number to avoid ambiguity.
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 demi@nickel-alloy.com 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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