EN 10028-7 specifies requirements for flat products (plates and strips) of stainless and heat-resistant steels intended for pressure equipment. It is the primary material standard for austenitic and duplex stainless steel plates used in pressure vessels designed to EN 13445. If you are selecting 316L, 304L, duplex 2205, or super duplex 2507 for a pressure vessel — this is the standard your material certificates must reference.
- Scope and Application Range
- Grade System and Steel Designations
- Austenitic Grades: Properties and Selection
- Duplex Grades: 1.4462 and 1.4410
- Heat Treatment Conditions
- Mechanical Properties at Elevated Temperature
- Impact Testing Requirements
- Inspection, Testing, and EN 10204 Certificates
- Cross-Standard Map
- Common Selection and Procurement Errors
1. Scope and Application Range
EN 10028-7 covers flat stainless and heat-resistant steel products (plates ≥ 3 mm, strip ≥ 0.35 mm thickness) for pressure purposes. The standard is part of the EN 10028 family:
- EN 10028-2 — elevated temperature carbon and low-alloy ferritic steels (P235GH, P265GH, P355GH, 13CrMo4-5, 10CrMo9-10)
- EN 10028-3 — weldable fine-grain ferritic steels (P275N, P355N, P460N)
- EN 10028-7 — austenitic stainless, duplex, and heat-resistant steels ← this standard
Part 7 applies to plates used in: pressure vessels per EN 13445, industrial piping per EN 13480, heat exchangers, reactors, and storage vessels operating from cryogenic temperatures to ≥ 550°C.
2. Grade System and Steel Designations
EN 10028-7 uses the steel number system of EN 10027-2. Grades are identified by a four-digit number starting with 1.4xxx for stainless steels. The designation includes the product form (plate/strip) and heat treatment condition. Common format on a mill certificate:
Where: 1.4404 = steel number, AT = heat treatment condition
3. Austenitic Grades: Properties and Selection
Austenitic stainless steels are the most widely used grades in pressure vessel fabrication. They offer excellent corrosion resistance, good weldability (no preheat required for most thicknesses), and retain adequate ductility at cryogenic temperatures. The most common EN 10028-7 austenitic grades:
| Steel Number | Common Name | UNS / AISI | Key Composition Features | Typical Application |
|---|---|---|---|---|
| 1.4301 | 304 | S30400 | 18% Cr, 8–10.5% Ni, max 0.07% C | General pressure service, water, mild chemicals — not seawater |
| 1.4307 | 304L | S30403 | 18% Cr, 8–10% Ni, max 0.030% C (low carbon) | Welded vessels where PWHT is not performed — low C prevents sensitisation |
| 1.4401 | 316 | S31600 | 17% Cr, 10–13% Ni, 2–2.5% Mo | Chemical process, dilute acids, mild chloride environments |
| 1.4404 | 316L | S31603 | 17% Cr, 10–13% Ni, 2–2.5% Mo, max 0.030% C | Most common selection for welded pressure vessels — 316 properties, low C for weldability |
| 1.4571 | 316Ti | S31635 | 17% Cr, 10–13% Ni, 2–2.5% Mo, Ti stabilised (Ti ≥ 5×C) | Higher-temperature service (>400°C) where sensitisation risk exists; less common in new designs (1.4404 preferred) |
| 1.4435 | 316L (higher Mo) | S31603 | 17% Cr, 12–15% Ni, 2.5–3% Mo, max 0.030% C | Pharmaceutical and chemical service — higher Ni+Mo for improved pitting resistance |
| 1.4541 | 321 | S32100 | 17–19% Cr, 9–12% Ni, Ti stabilised | High-temperature vessels (400–800°C) — Ti stabilisation prevents intergranular corrosion |
Room-temperature minimum mechanical properties (representative values)
| Grade | Rp0.2 min (MPa) | Rm min (MPa) | A5 min (%) | Hardness max (HBW) |
|---|---|---|---|---|
| 1.4307 (304L) | 175 | 480 | 40 | 215 |
| 1.4404 (316L) | 170 | 480 | 40 | 215 |
| 1.4435 (316L high Mo) | 170 | 480 | 40 | 215 |
| 1.4541 (321) | 195 | 510 | 40 | 215 |
| 1.4571 (316Ti) | 195 | 510 | 40 | 215 |
4. Duplex Grades: 1.4462 and 1.4410
Duplex stainless steels have a two-phase microstructure (austenite + ferrite, approximately 50/50) that gives them higher yield strength than austenitic grades and better resistance to stress corrosion cracking (SCC) in chloride environments. EN 10028-7 covers the two most common duplex grades:
| Steel Number | Common Name | Composition | PREN | Rp0.2 min (MPa) | Rm (MPa) |
|---|---|---|---|---|---|
| 1.4462 | 2205 (duplex) | 22% Cr, 5% Ni, 3% Mo, 0.17% N | ~34–36 | 450 (plate ≤40 mm) | 620–880 |
| 1.4410 | 2507 (super duplex) | 25% Cr, 7% Ni, 4% Mo, 0.27% N | ~41–43 | 550 (plate ≤40 mm) | 750–1000 |
The higher yield strength of duplex grades relative to 316L (~450 MPa vs ~170 MPa) can significantly reduce wall thickness in pressure vessel design — a 316L vessel at 100 bar may require 30% more wall thickness than the equivalent 1.4462 vessel. This is an important cost driver for large-diameter high-pressure vessels.
5. Heat Treatment Conditions
EN 10028-7 §7 specifies the delivery conditions (heat treatment states) for each grade. The condition code appears on the material certificate:
| Condition Code | Name | Process | Notes |
|---|---|---|---|
| +AT | Solution annealed (quenched) | Heat to solution temperature, rapid quench (water or air) | Standard delivery condition for all austenitic and duplex grades — restores corrosion resistance after hot working |
| +AW | As-welded (no PWHT) | Not a mill condition — refers to final fabricated state | Low-carbon grades (1.4307, 1.4404) designed to be used in this condition without sensitisation risk |
| +CR | Cold rolled | Cold reduction without annealing | Higher strength but sensitisation risk; not typical for pressure vessel plate |
For duplex grades (1.4462, 1.4410), the solution annealing temperature and cooling rate are critical to maintaining the ferrite/austenite balance. Under-annealing (too low temperature or too slow cooling) leaves sigma phase or chi phase in the microstructure — both of which embrittle the steel and reduce corrosion resistance. EN 10028-7 specifies minimum solution anneal temperatures: 1020°C for 1.4462, 1070°C for 1.4410, followed by rapid water quench.
6. Mechanical Properties at Elevated Temperature
EN 10028-7 Annex A provides Rp0.2/T (yield strength at temperature T) for each grade — these values feed directly into the allowable stress calculation per EN 13445-3 §6.1. Key design considerations:
| Grade | Rp0.2 at 200°C (MPa) | Rp0.2 at 400°C (MPa) | Creep limit temperature |
|---|---|---|---|
| 1.4307 (304L) | ~125 | ~105 | Above ~550°C, creep rupture controls design |
| 1.4404 (316L) | ~127 | ~108 | Above ~550°C, creep rupture controls design |
| 1.4541 (321) | ~145 | ~120 | Stabilisation extends service to ~650°C before creep controls |
| 1.4462 (2205) | ~380 | ~290 | Max service temperature ~300°C (embrittlement risk above ~280°C) |
7. Impact Testing Requirements
EN 10028-7 §8.3 specifies impact testing requirements. For austenitic grades, routine Charpy testing is generally not required at the minimum design temperature because austenitic stainless steels do not exhibit ductile-to-brittle transition — they retain adequate toughness to cryogenic temperatures (−196°C for 304L/316L).
However, impact testing IS required in EN 10028-7 when:
- Specified by the purchaser for quality verification
- Required by the applicable design standard (EN 13445-2 §4.4 may require test evidence for heavy section plates)
- The grade is duplex — duplex grades are impact tested at 0°C or the specified temperature, with a minimum requirement of 40 J average at 0°C (stricter than ferritic grades)
8. Inspection, Testing, and EN 10204 Certificates
EN 10028-7 §9 defines the inspection and testing requirements. The default inspection document type follows EN 10204:
| Certificate Type | EN 10204 Reference | Content | When Required |
|---|---|---|---|
| 2.1 Declaration | §2.1 | Manufacturer declares compliance with the order — no test data | Non-pressure parts only |
| 2.2 Test report | §2.2 | Non-specific inspection: manufacturer's standard test results, not cast-specific | Low-risk applications, Cat I PED |
| 3.1 Inspection certificate | §3.1 | Specific inspection: cast/heat-specific test results, signed by manufacturer's authorised inspector | Pressure-retaining parts Cat II/III — minimum standard for EN 13445 pressure vessels |
| 3.2 Inspection certificate | §3.2 | Specific inspection: test witnessed by purchaser's representative or independent third party | Cat IV PED vessels, safety-critical parts with Notified Body witness requirement |
Beyond the certificate type, EN 10028-7 mandates heat analysis (chemical composition per cast), product analysis (per plate), mechanical tests per heat and thickness range, and surface condition inspection. Each plate must carry a traceable marking with steel number, heat number, plate number, and thickness — essential for maintaining EN 13445-2 material traceability through fabrication.
9. Cross-Standard Map
| Standard | Relationship to EN 10028-7 |
|---|---|
| EN 13445-2 | Uses EN 10028-7 as the material source; §4.3 lists approved grades; EN 10028-7 certificate required to qualify material for pressure service |
| EN 13445-3 | Elevated temperature Rp0.2/T from EN 10028-7 Annex A feeds allowable stress calculation in §6.1 |
| EN 10204 | Certificate type (2.2/3.1/3.2) specified by EN 10028-7 §9 and required by PED/EN 13445-2 for pressure parts |
| NORSOK M-001 | Restricts duplex (1.4462, 1.4410) in CP environments (HISC risk); requires PREN ≥ 24 for most seawater wetted surfaces (satisfied by 316L/1.4404 but not 304L/1.4307) |
| DNV-RP-F112 | HISC design limits for duplex in cathodically protected service — applies when EN 10028-7 duplex grades used on subsea or offshore equipment with CP |
| ISO/TR 15608 | EN 10028-7 austenitic grades → Group 8; duplex → Group 10. Controls WPS/WPQR coverage under EN 13445-2 welding requirements |
| PED 2014/68/EU | Materials must be from EN 10028-7 or approved equivalent to be included in a harmonised standard-based PED conformity assessment |
10. Common Selection and Procurement Errors
Grade selection errors
- Specifying 304/1.4301 (standard carbon) instead of 304L/1.4307 for a welded vessel without post-weld solution annealing — standard 304 with 0.07% C max is susceptible to sensitisation in the heat-affected zone, reducing intergranular corrosion resistance; 304L (≤0.030% C) is used in the as-welded condition for this reason
- Using duplex 1.4462 on a process vessel that intermittently reaches 320°C — sigma phase embrittlement begins above ~280°C; cyclic operation that crosses this threshold repeatedly will degrade toughness over time; austenitic 1.4404 or stabilised 1.4541 is appropriate for this temperature range
- Selecting 316L (1.4404) for a strongly reducing acid environment (e.g. concentrated H₂SO₄ or HF) based on "stainless is resistant" — 316L's corrosion resistance relies on the passive film; in strongly reducing or halide-rich environments it breaks down rapidly. Material selection for aggressive process chemicals requires a corrosion engineer review, not a table lookup
Certificate and procurement errors
- Accepting a 2.2 test report (non-specific inspection) for a pressure vessel plate when EN 13445-2 requires a specific 3.1 certificate — the 2.2 certificate uses typical test results from the grade, not the specific cast and plate being installed; the vessel's MDR will not satisfy the Notified Body review
- Ordering to steel number only (e.g. "1.4404") without specifying the heat treatment condition (+AT), mechanical property class, and EN 10028-7 explicitly — a supplier may deliver material to a different national standard or delivery condition that is technically different but similar enough to pass a visual check
- Not verifying that the plate marking is cast/heat traceable before cutting — once traceability is lost (plate cut without marking transfer), the material cannot legally be used as a pressure part under EN 13445 without re-testing the cut pieces at the purchaser's cost; EN 10028-7 §10.3 and EN 13445-2 §4.5 both require marking transfer at every stage of cutting and forming
Ask the Leide Navigator about EN 10028-7
EN 10028-7 (45 chunks), EN 13445-2 (81 chunks), and NORSOK M-001 (29 chunks) are all in the Leide Navigator. Ask about grade properties, heat treatment requirements, elevated-temperature allowable stress, HISC limits for duplex, or specific clause interpretations — cited answers in under 3 seconds.