Technical knowledge
Inconel 625 weld overlay: the economical way to buy corrosion resistance
How Inconel 625 weld overlay and cladding work on carbon steel flanges and fittings: process options, dilution control, thickness, inspection and when solid alloy is still the better answer.
Process options and what they give you
- Manual or mechanised gas tungsten arc welding. Low dilution and precise control, preferred for sealing faces and small bore bores.
- Submerged arc or electroslag strip cladding. High deposition rate for large surfaces, with dilution managed through the flux and the number of layers.
- Explosion bonding or roll bonding. Produces a metallurgically bonded clad plate used for spades, blinds and vessel components.
Dilution is the controlling variable. The first layer picks up iron from the substrate, which lowers the molybdenum and niobium content of the deposit. Two layers are normally specified so that the surface chemistry meets the 625 requirement after dilution.
Thickness, coverage and where overlay belongs
| Area | Typical finished thickness | Notes |
|---|---|---|
| Raised face and groove | 3 mm minimum after machining | Verify by positive material identification after final machining |
| Bore | 2 to 4 mm | Mechanised welding gives the most consistent coverage |
| Ring type joint groove | Full coverage plus hardness agreement | Confirm the groove is harder than the ring |
| Weld end bevel | Butter to complete the transition | Allows a matching filler joint to the pipe |
Inspection that must be written into the order
- Dye penetrant examination of the finished overlay surface after machining.
- Ultrasonic examination for bond integrity where the design requires it.
- Positive material identification of the finished surface to confirm the chemistry after dilution, not just of the filler wire.
- Thickness verification at defined locations, with a minimum finished thickness stated in the purchase order.
- Documentation of the welding procedure specification, procedure qualification record and welder or operator qualification.
When solid alloy is still the better answer
Overlay is not always cheaper or safer. Choose solid Inconel 625 when the section is thin, when the component will be repeatedly machined or repaired, when the service temperature creates a large thermal expansion mismatch with the substrate, or when the geometry makes consistent coverage impossible to achieve and verify.
Questions about this topic
How thick should an Inconel 625 overlay be?
A finished thickness of 3 mm minimum after machining is common for sealing faces, with at least two weld layers so that iron dilution from the substrate does not reduce the surface chemistry below specification requirements.
Can overlay be repaired in the field?
Local repairs are possible with the same qualified procedure and filler, followed by re-machining and re-examination. Repeated repair of the same area usually indicates a coverage or dilution problem that should be addressed at source.
Is an overlay flange as strong as a solid flange?
The load bearing capacity comes from the carbon steel substrate, which is typically stronger and cheaper than solid nickel alloy. The overlay only provides the corrosion barrier, so the design must keep the allowable stresses of the substrate.
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.
Talk to an engineer
Share your duty conditions and we will shortlist candidate alloys within one working day.