Technical knowledge
Post weld heat treatment of nickel alloys: when to specify and when to avoid
Why most nickel alloy welds need no post weld heat treatment, when stress relief and solution annealing are justified, the temperature ranges that must be avoided, and how to record the cycle.
Decide by strengthening mechanism
| Alloy type | Typical approach | Reason |
|---|---|---|
| Solid solution, such as 625 and C-276 | No PWHT for corrosion service | No strength gain; risk of precipitation |
| Precipitation hardening, such as 718 and X-750 | Post weld age | Required to develop strength |
| Stabilised, such as 825 and 347 | None normally | Stabilisation prevents sensitisation |
| Commercially pure nickel and Monel | None normally | No precipitation response to exploit |
The range to avoid
For many nickel alloys, prolonged exposure between roughly 540 and 870 C precipitates carbides and intermetallic phases at grain boundaries. This reduces toughness and, in some alloys, corrosion resistance. Stress relieving cycles that fall in this band should be avoided, and any thermal treatment should be agreed with the materials engineer before it is applied.
When stress relief or solution annealing is justified
- Dimensional stability of a heavily machined assembly.
- Code requirement for a specific service or thickness.
- Dissimilar joints where the design engineer has assessed the expansion mismatch.
- Cold worked components that have exceeded the permitted strain for the service.
Recording the cycle
Whenever heat treatment is applied, require a chart showing furnace identification, load arrangement, set point, actual temperatures, soak time and cooling method. A certificate line that states only the nominal treatment is not evidence that the cycle was achieved, and it is the first thing an auditor will challenge.
Questions about this topic
Does every nickel alloy weld need stress relieving?
No. Solid solution alloys such as Inconel 625 and Hastelloy C-276 are normally used as welded. Unnecessary thermal exposure in the intermediate range can reduce toughness and corrosion resistance.
Can I stress relieve Inconel 625 at 650 C?
That temperature sits in the range where secondary phases precipitate. If stress relief is genuinely required, agree a cycle with the materials engineer and verify the properties afterwards.
Why does Inconel 718 need a post weld age?
Because its strength comes from precipitation hardening. Without the age, the weldment remains in a low strength condition and will not meet the design properties.
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.
Talk to an engineer
Share your duty conditions and we will shortlist candidate alloys within one working day.