Technical knowledge
Machining and welding Inconel 625 flanges: shop practice that works
Practical shop guidance for Inconel 625: tooling, cutting speeds, work hardening control, weld procedure essentials, filler selection and how to avoid the defects that cause rework.
Machining: keep the cut engaged
625 work hardens rapidly and has poor thermal conductivity, so heat stays in the chip and the surface layer hardens. A light pass over an already hardened skin quickly destroys tool life.
- Depth of cut. Keep the feed and depth high enough to cut below the previously work hardened layer rather than rubbing over it.
- Tool geometry. Positive rake, sharp edges, rigid setup. Replace inserts on a scheduled basis rather than on failure.
- Coolant. High pressure coolant improves chip breaking and reduces surface hardening on the sealing face.
- Speeds. Run slower than for stainless steel and accept a lower metal removal rate; forcing the rate is the usual cause of a ruined flange face.
Welding: the five things that decide quality
- Cleanliness. Remove all paint, oil, marking crayon and embedded iron. Use dedicated stainless wire brushes and separate grinding wheels for nickel alloys.
- Filler metal. ERNiCrMo-3 for gas tungsten and metal inert gas welding, ENiCrMo-3 for covered electrodes.
- Shielding. Use argon backing plus trailing shields. Straw or blue oxide on the root indicates inadequate shielding and must be removed and rewelded.
- Heat input. Moderate heat input with an interpass temperature below about 150 C limits grain growth and distortion.
- Distortion control. Balance the weld sequence on flanges so the sealing face stays flat within ASME B16.5 facing tolerances.
Defects, causes and fixes
| Defect | Typical cause | Corrective action |
|---|---|---|
| Root oxidation or sugaring | No backing gas | Purge with argon, verify oxygen content, remove and reweld |
| Lack of fusion | Heat input too low, poor bevel | Increase heat input, open the included angle, improve access |
| Solidification cracking | High restraint, contamination by sulphur or lead | Improve cleanliness, adjust bead shape, reduce restraint |
| Poor tool life | Light finishing cuts on worked skin | Increase depth of cut, sharpen or replace inserts |
| Iron contamination | Shared tooling with carbon steel | Dedicated tools, pickling or passivation, ferroxyl test |
Verification before release
Confirm dye penetrant examination on all machined sealing surfaces, positive material identification on the required percentage of pieces, dimensional check of the facing and bolt circle to the applicable ASME standard, and a review of the heat treatment chart. Where the project requires independent verification, arrange sampling and laboratory testing by SGS and issue the resulting third party test report with the shipment.
Questions about this topic
Does Inconel 625 need preheat?
No. Preheat is not required and is generally not recommended because it increases the time in the temperature range where secondary phases can form. Dry the joint thoroughly and remove any condensation instead.
Why do my inserts fail so fast on 625?
Usually because the previous pass work hardened the surface and the next pass is too light to cut through it. Increase the depth of cut, keep the feed up, and never stop feeding while the tool is in contact.
Can I weld 625 to carbon steel directly?
Yes, with control. Butter the carbon steel face with ERNiCrMo-3 first, then complete the joint. This prevents the dilution zone from forming a hard, crack sensitive martensitic band. Post weld heat treatment for stress relief should be agreed with the design engineer.
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.