Steel Grade Technical Center

A practical reference to stainless steel and nickel alloy grades used in pipe, tube and fittings, with related materials included for comparison. Identify candidate grades by metallurgical family, confirm the UNS designation, and check the product form, manufacturing route, specification edition and delivery condition required by your project. Availability is confirmed in the quotation.

How to use this center

1. Define the service conditions. Include temperature, pressure, fluid composition, concentration, chlorides, oxidising species, flow conditions and relevant corrosion risks.
2. Confirm the grade and product form. A UNS designation identifies an alloy; it does not define the manufacturing route, dimensions, delivery condition or complete inspection requirements.
3. Specify the standard and edition. Check that the grade and manufacturing route are covered by the ordered edition. Product specifications, general requirements and design codes have different roles.
4. Check acceptance and traceability. The purchase order, applicable specification and design code govern acceptance. The inspection certificate reports results for the relevant heat or test lot and must be traceable to the supplied product. EN 10204 type 3.1 is an inspection document type, not a separate product approval.

1. Austenitic Stainless Steels: 200 and 300 Series

Austenitic stainless steels are widely used in process water, food and beverage equipment, heat exchangers and chemical piping. Suitability depends on the actual medium and fabrication condition. They generally have low magnetic permeability in the solution-annealed condition, but cold work or retained ferrite can affect magnetic response. They are not hardenable by conventional quench-and-temper treatment; cold work increases strength.

316 and 316L contain 2.0–3.0% molybdenum in ASTM A312/A312M-25 and A213/A213M-25, improving resistance to pitting compared with common 304 grades under comparable conditions. Low-carbon grades reduce the risk of weld-related sensitisation; they do not guarantee freedom from sensitisation under every thermal exposure. In these editions, TP304L and TP316L normally have a 0.035% maximum carbon limit, subject to the applicable table notes for certain small-diameter or thin-wall products requiring many drawing passes. Do not apply one carbon limit to all L grades or standards.

321 and 347 use titanium and niobium stabilisation respectively to reduce susceptibility to chromium-carbide-related intergranular corrosion. H grades have controlled carbon and other requirements for elevated-temperature service. Creep, oxidation, exposure duration, welding and the governing design code determine the usable temperature range; a grade name alone does not establish a design temperature. 317 and 317L offer increased molybdenum for suitable chemical and pulp-processing environments.

2. High-Temperature and Super Austenitic Grades

This group includes oxidation-resistant and high-temperature grades such as 309S, 310S/H, 314 and 253 MA, as well as high-alloy austenitic grades such as 904L, 254 SMO, 926 and Alloy 31 for demanding aqueous corrosion environments. 310MoLN is associated with urea and carbamate applications, subject to project-specific quality and corrosion requirements. Product-standard coverage must be checked for each grade; 310/S31000 and 314/S31400 are retained below as material references rather than asserted A312/A213 tubular grades.

High-alloy austenitic grades can provide substantially better resistance to chloride stress corrosion cracking (SCC) than conventional 304L and 316L. Where SCC governs selection, compare suitable high-alloy austenitic, duplex, super duplex and nickel alloy candidates using representative corrosion data. PREN is a composition-based indicator of relative pitting resistance, not proof of SCC resistance or fitness for service. Use the specified formula, certified composition and any additional contractual minimum.

3. Duplex Stainless Steels

Properly solution-treated duplex stainless steels contain ferrite and austenite. Common duplex grades solidify predominantly as ferrite, with austenite forming during subsequent cooling. Final phase balance and properties depend on composition, processing and thermal history. In comparable solution-annealed conditions, 2205 typically has about twice the proof strength of common 304L/316L grades and substantially better resistance to chloride SCC. Duplex steels can still crack under sufficiently severe conditions, and strength comparisons do not replace design allowable stresses.

S31803 and S32205 are distinct UNS designations commonly associated with 2205. S32205 has tighter composition requirements. Dual certification requires compliance with all applicable requirements for both designations under the ordered product specification and edition. 3RE60/S31500 remains relevant to heat-exchanger and existing project specifications; substitution requires review of the original design and service conditions.

ASTM A928/A928M covers electric-fusion-welded duplex pipe with filler metal. It is not a seamless product specification. For welded procurement, confirm the individual grade, class, examination and edition separately.

4. Super Duplex and Other High-Alloy Duplex Grades

2507/S32750 and S32760 are common candidates for demanding chloride-bearing environments, including seawater and offshore service. S32760 includes copper and tungsten additions. Other high-alloy duplex grades are included for reference, but family labels and chromium content alone do not guarantee a particular PREN or interchangeable corrosion performance. Verify the specified formula, product-standard table notes and any manufacturer or project requirements.

Composition, solution treatment, cooling, phase balance and fabrication all affect performance. Confirm delivery condition, traceability and the inspections required by the project. For oil and gas production or natural-gas sweetening involving H₂S within the scope of ISO 15156-3 / NACE MR0175, assess material condition and welding against the relevant provisions and the actual temperature, H₂S partial pressure, in-situ pH and chloride level. Grade, PREN or hardness alone does not establish suitability.

5. Nickel Alloys: Inconel and Incoloy

Nickel-chromium alloys 600 and 601 are used in selected high-temperature oxidation and carburisation environments. Alloy 625 combines corrosion resistance with useful strength over a broad temperature range; it is not a universal replacement for creep-designed furnace alloys. Age-hardenable 718 is selected for high strength, with performance dependent on heat treatment, temperature and exposure duration.

800, 800H and 800HT are iron-nickel-chromium alloys. Controlled composition, grain size and heat treatment distinguish the elevated-temperature creep applications of 800H/800HT. Compare the actual design temperature, exposure time and code allowable stresses rather than assuming a universal strength ranking. Alloy 825 is used in suitable sulphuric and phosphoric acid environments. Age-hardenable 925 requires its specified condition and a separate environmental qualification where sour service is involved.

6. Nickel Alloys: Hastelloy, Monel, Nickel and Other Ni Alloys

High-molybdenum, low-chromium B-2 and B-3 alloys are candidates for selected reducing-acid environments, including hydrochloric acid; oxidising contamination can substantially change their performance. Chromium-molybdenum C-type alloys cover a different range of mixed-acid and chloride environments. Selection requires concentration, temperature and impurity data.

Alloy 400 is used in selected hydrofluoric-acid, seawater and alkaline applications. HF selection requires attention to water content, temperature, phase and oxidising contamination. K-500 is an age-hardenable nickel-copper alloy commonly used in shafts and valve components; its B865 bar/forging specification is not a seamless pipe standard. Nickel 200 and low-carbon Nickel 201 are used for suitable caustic duties. Low carbon in 201 helps address the elevated-temperature graphitisation concern associated with Nickel 200; the design code and actual exposure still govern. Food-contact suitability requires separate verification. Alloy 20 is associated with sulphuric-acid processing; N08120 is a high-temperature iron-nickel-chromium alloy whose performance must be compared at the design conditions.

7. Ferritic and Martensitic Stainless Steels

Ferritic and martensitic stainless steels have different corrosion, strength and fabrication characteristics. Selected grades are used as tubing under ASTM A268/A268M, subject to the grades and conditions covered by the specified edition. Other entries below refer mainly to bar, forgings, sheet or strip. A related material entry is not an offer to supply every form. Verify the exact UNS variant, heat treatment, weldability and corrosion requirements before specifying.

8. Precipitation-Hardening Grades

Precipitation-hardening stainless steels develop high strength through specified heat treatment. Properties depend on the solution-treated and aged condition, product form and applicable standard. The entries below are related material references; tube availability and its acceptance specification require separate confirmation.

9. Compatible Butt-Welding Fittings

Compatible butt-welding fittings may be specified under ASTM A403/A403M, A815/A815M or B366/B366M, subject to the grades and forms covered by the ordered edition. The fitting material must satisfy the project design and connection requirements; it need not always have the identical designation as the mating pipe. Confirm grade, class, manufacturing route, heat treatment, examination requirements and any supplementary requirements.

Where ASME B16.9 applies, verify fitting dimensions, tolerances and connection-end compatibility with the mating pipe and the design requirements. A matching schedule alone is not a complete wall-thickness or pressure-design check. Certification should identify the product standard and edition, fitting grade/class, applicable UNS designation, test results and traceability. A UNS designation identifies the alloy; it is not a stand-alone testing specification.

Grade selection by service environment

These are candidate materials for a technical review, not an automatic selection or a ranking. Record temperature, pressure, concentration, chloride level, pH, oxidising impurities, flow/stagnation, crevices, stress and fabrication condition. Pressure design, sour-service requirements, hygienic/contact approvals and any project-specific rules must be checked separately.

Grade data tools

Companion calculators on this site for working with the values behind these grades.

Specifications behind these grades

Use these references to locate the applicable product specification. Confirm its edition, grade coverage, delivery condition and any supplementary requirements against the order. General requirements supplement the product specification; they do not replace it.

• Stainless pipe: ASTM A312, ASTM A999 (general requirements)
• Stainless tube: ASTM A213, ASTM A269, ASTM A270, ASTM A1016 (general requirements)
• Duplex pipe and tube: ASTM A790, ASTM A789
• Nickel alloy pipe and tube: ASTM B161, ASTM B163, ASTM B165, ASTM B167, ASTM B407, ASTM B423, ASTM B444, ASTM B622, ASTM B729, ASTM B983
• Sour service and alternative systems: NACE MR0175, ISO 15156-3, EN 10216-5

Reference sources and editions

Selected data were checked against ASTM A213/A213M-25, A312/A312M-25, A269/A269M-25, A789/A789M-24, A790/A790M-24, B163-22 and B622-23. These identify the editions used for this reference; the contract edition governs each order. Manufacturer data apply to the specified material and condition and must not be treated as a universal service limit.

Further reading: 254 SMO corrosion data; 2202 manufacturer data; ASTM B983 scope (historical edition). Commercial and trade names are included for identification; the quotation and certificate identify the actual manufacturer, grade and agreed specification. A matching UNS designation alone does not establish branded origin.

Frequently asked questions