Technical knowledge
Material selection for sour service: an H2S decision path
How to select materials for hydrogen sulphide service: the cracking mechanisms involved, the role of hardness and heat treatment, the usual alloy ladder and the information you need before shortlisting.
The mechanisms you are guarding against
| Mechanism | Driving condition | Control |
|---|---|---|
| Sulphide stress cracking | Hard material plus tensile stress plus H2S | Hardness limit, correct heat treatment |
| Hydrogen induced cracking | Hydrogen absorbed into steel | Clean steel, controlled inclusions |
| Stress oriented hydrogen induced cracking | HIC plus stress | Steel quality, stress control |
| Stress corrosion cracking | Chlorides plus temperature plus H2S | Alloy selection, hardness |
| Pitting and crevice | Chlorides and stagnation | Higher alloy, geometry |
Information to collect before shortlisting
- Hydrogen sulphide partial pressure and whether it varies with upset conditions.
- pH of the aqueous phase and whether it is buffered.
- Chloride content and total dissolved solids.
- Presence of elemental sulphur, which changes the requirements materially.
- Maximum and minimum operating temperature, including shutdowns.
- Whether the system is inhibited, and with what.
The usual ladder
- Carbon and low alloy steel within the limits of the standard, with hardness control.
- Duplex 2205 for moderate conditions with chlorides.
- Incoloy 825 for produced water and moderate sour conditions.
- Inconel 625 for severe conditions and elemental sulphur.
- Inconel 718 where high strength bolting is needed in the aged condition.
Documentation and verification
Quote the standard edition and the environmental parameters on the purchase order. Require the heat treatment condition, actual hardness readings, the heat treatment chart and the weld procedure qualification. 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
Does elemental sulphur change the selection?
Yes, materially. It makes the environment considerably more aggressive and generally pushes the selection toward higher nickel alloys such as Inconel 625. Always state whether elemental sulphur is present.
Is a lower hardness always safer?
Lower hardness reduces susceptibility to sulphide stress cracking, but the material must still meet the mechanical requirements of the design. The goal is to stay within the hardness limit while meeting the design strength.
Can I use duplex 2205 in sour service?
Yes within the limits of the applicable edition, provided it is correctly solution annealed and within the hardness limit. Confirm the specific environmental parameters before committing.
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.