Technical knowledge
Incoloy 825 for sulphuric and phosphoric acid piping
Incoloy 825 composition, acid resistance, temperature limits and specification notes for flanges, fittings and seamless tube in sulphuric, phosphoric and sour produced water service.
Why 825 sits where it does in the price and performance ladder
Incoloy 825 was designed as an iron nickel chromium alloy with deliberate additions of molybdenum, copper and titanium. The nickel level removes chloride stress corrosion cracking, the molybdenum handles pitting, the copper helps in reducing acids such as sulphuric, and titanium stabilises the structure against sensitisation so welded components do not lose intergranular resistance.
Composition and properties
| Element | Range | Contribution |
|---|---|---|
| Nickel | 38.0 - 46.0 % | Chloride stress corrosion cracking resistance |
| Chromium | 19.5 - 23.5 % | Oxidising acid and passivity |
| Molybdenum | 2.5 - 3.5 % | Pitting and crevice resistance |
| Copper | 1.5 - 3.0 % | Reducing acid performance |
| Titanium | 0.6 - 1.2 % | Stabilisation against sensitisation |
| Iron | 22 % minimum | Cost control |
| Typical PREN | 30 - 33 | Above 316L, below 625 |
Where it performs and where it does not
- Sulphuric acid up to about 40 % concentration. Copper plus molybdenum give useful resistance at moderate temperature; above that, move to a high molybdenum alloy.
- Phosphoric acid production. Widely used in evaporators and piping, though fluoride and chloride content can push the duty beyond 825.
- Sour produced water and gas. Listed in NACE MR0175 / ISO 15156 and commonly used for tubing, flanges and fittings.
- Seawater with moderate temperature. Acceptable in flowing, aerated conditions; stagnant warm seawater favours 625 or super duplex.
- Avoid strong hydrochloric acid. That is the territory of Hastelloy B-3 or C-276.
Specifying flanges, fittings and tube in 825
Order forged flanges to ASTM B564 and wrought butt weld fittings to ASTM B366, both to UNS N08825, with seamless tube to ASTM B423 or B163 as applicable. State the stabilising anneal, require positive material identification, and ask for the certificate to quote molybdenum and copper since those two elements decide performance in reducing acid and are the first thing to drift in a non conforming heat.
Questions about this topic
Is Incoloy 825 the same as Alloy 825?
Yes. Incoloy 825, Alloy 825 and UNS N08825 describe the same nominal composition. Use the UNS number in procurement documents so the requirement is not tied to a single trademark.
Can 825 be used for hydrochloric acid?
Only at very low concentration and temperature. For hydrochloric acid duty, Hastelloy B-3 is the established choice, with C-276 used where oxidising contaminants are also present.
Does 825 need post weld heat treatment?
No, and it is generally avoided. Titanium stabilisation means welded components resist sensitisation in the as welded condition, which is one of the alloy's main practical advantages over unstabilised austenitic grades.
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.