EN 1011-2 Preheat Standard: CET Carbon Equivalent, Preheat Tables, and Tempilstik® Selection
Welding engineers in Vietnam are well acquainted with AWS D1.1 and ASME — but when working on EPC projects led by European contractors such as TechnipFMC, Saipem, or McDermott's European operations, WPS and PQR documents frequently reference EN 1011-2. This is the European standard for preheat and weld thermal control for steel, and its core difference from AWS lies in the carbon equivalent formula: it uses CET (a dedicated formula distinct from the familiar IIW CE) and introduces heat input into the preheat calculation. A solid understanding of EN 1011-2 allows QA/QC engineers to read WPS documents, look up preheat requirements, and select the correct Tempilstik® grade without guesswork.
What Is EN 1011-2 and When Does It Apply?
EN 1011-2 — full title: Welding — Recommendations for welding of metallic materials — Part 2: Arc welding of ferritic steels — is the European standard that sets out technical recommendations for arc welding of ferritic steels, including carbon steel, low-alloy steel, and higher-alloy steel (austenitic stainless steels are excluded).
This standard appears in project technical documentation when:
- The contract specifies EN standards rather than ASME/AWS — typically driven by a European client or main contractor
- The design code is EN 13480 (industrial piping) or EN 13445 (pressure vessels) rather than ASME B31.3 / Section VIII
- WPS/PQR qualification is carried out to EN ISO 15614-1 rather than ASME Section IX or AWS D1.1
- The project is destined for EU markets or requires CE marking on pressure-retaining equipment
The CET Formula — the Core Difference from AWS
AWS D1.1 uses the IIW Carbon Equivalent formula:
EN 1011-2 uses a different formula called CET, optimised for modern low-alloy steels:
Two key differences between CE (IIW) and CET:
- Mn weighting: CE uses Mn/6 (higher influence); CET uses Mn/10 — CET assigns lower hardenability weight to manganese
- Ni weighting: CE uses Ni/15; CET uses Ni/40 — CET significantly discounts the contribution of nickel
- Mo grouping: CE groups Mo with Cr and V; CET groups Mo with Mn — reflecting different metallurgical behaviour in low-alloy steels
The practical result: for the same steel grade, CET is generally lower than CE (IIW), and preheat requirements per EN 1011-2 are sometimes lower than under AWS D1.1. This is not a deficiency in the standard — it reflects a different metallurgical approach, not a lower level of safety.
Worked example: CET calculation for S355J2 (comparable to A572 Gr.50)
Typical composition of S355J2 per EN 10025-2: C = 0.20%, Mn = 1.50%, Si = 0.40%, Cr = 0.30%, Cu = 0.35%, Ni = 0.30%, Mo = 0.08%
A CET of 0.40 is then entered into the EN 1011-2 preheat table together with material thickness and heat input to determine the required preheat temperature (see table below).
EN 1011-2 Preheat Table — Method A (Simplified)
EN 1011-2 provides two calculation methods: Method A (simplified, using CET and material thickness) and Method B (more complete, incorporating heat input and hydrogen content). The table below is based on Method A — the most widely used approach in practice:
| CET | Thickness ≤ 25 mm (1") | 25 < t ≤ 40 mm | 40 < t ≤ 60 mm | 60 < t ≤ 100 mm | Tempilstik® Part No. |
|---|---|---|---|---|---|
| ≤ 0.25 | — | — | — | — | Not required |
| 0.25 – 0.35 | — | — | 50°C (122°F) | 100°C (212°F) | #28016 (107°C / 225°F) |
| 0.35 – 0.45 | — | 50°C (122°F) | 100°C (212°F) | 150°C (302°F) | #28016 / #28318 |
| 0.45 – 0.55 | 50°C (122°F) | 100°C (212°F) | 150°C (302°F) | 200°C (392°F) | #28318 / #28327 |
| > 0.55 | 100°C (212°F) | 150°C (302°F) | 200°C (392°F) | 250°C+ (482°F+) | #28327 / refer to Method B |
Note: the table above is a simplified illustration derived from EN 1011-2 Table B.2 Method A. For production work, always consult the standard directly and consider Method B when heat input is low or joint restraint is high.
Heat Input — the Parameter EN 1011-2 Adds That AWS D1.1 Tables Do Not
The second major difference between EN 1011-2 and AWS D1.1: EN 1011-2 Method B incorporates heat input (energy deposited per unit weld length, kJ/mm) into the preheat calculation. Higher heat input means slower HAZ cooling, which reduces cold cracking risk and can lower the required preheat. Conversely, low heat input — such as a GTAW root pass on thin-wall pipe — means rapid cooling, and a higher preheat may be needed.
In field practice, Method B requires the welding engineer to log arc parameters (U, I, v) and calculate heat input before looking up the preheat. This is why many EN 1011-2 WPS documents in Vietnam still use the simplified Method A and accept a slightly more conservative preheat result.
EN 1011-2 vs AWS D1.1 — Similarities and Differences
| Criterion | AWS D1.1 | EN 1011-2 |
|---|---|---|
| Carbon equivalent | CE (IIW): C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 | CET: C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40 |
| Steel grouping | Groups I–IV by CE and yield strength | Continuous CET range (no fixed group boundaries) |
| Heat input in preheat calculation | No (table lookup by group and thickness) | Yes — Method B (optional) |
| Hydrogen content | H4/H8/H16 classification — optional influence on WPS | Incorporated in Method B via hydrogen designator HD |
| Primary application scope | Structural steel, offshore, O&G under US/ASME system | European projects, CE marking, EN piping/pressure vessels |
| Tempilstik® applicability | Full — all grades | Full — same part numbers |
For a detailed preheat look-up table by steel grade with Tempilstik® part numbers, see the Preheat Temperature Reference Table. For background on preheat principles and AWS D1.1 steel groupings, refer to Preheat Temperature for Carbon Steel Welding — AWS D1.1 and ASME.
Frequently Asked Questions
How different are CET and CE (IIW) in practice?
For typical low-carbon steel (C ≤ 0.20%, Mn ≤ 1.5%), CET is generally 0.03–0.08 lower than CE (IIW). The gap widens when Ni and Mn content are elevated — CET assigns a much smaller weight to nickel (Ni/40 versus Ni/15 in IIW). This can lead to a lower calculated preheat under EN 1011-2 than under AWS D1.1 for the same steel and thickness — not because the standard is less stringent, but because the two systems take different metallurgical approaches.
My project has a WPS to EN 1011-2 but uses Japanese steel (SM490) — how do I calculate preheat?
Obtain the chemical composition from the mill certificate for the SM490 heat (or from the maximum permitted values in JIS G 3106), calculate CET using the EN 1011-2 formula, then look up the preheat temperature from the CET and thickness table. Any steel — Japanese, Korean, or Vietnamese — can be evaluated with CET as long as the full chemical composition is available. The standard does not restrict its application to EN-designated steels.
Which Tempilstik® grade is correct for a 50°C (122°F) preheat requirement per EN 1011-2?
Tempilstik® #28002 (109°F / 43°C) confirms the surface has reached 43°C. At this low preheat level — which is close to ambient temperature in Vietnam (28–38°C) — the more critical checks are confirming that no surface moisture is present and that the base metal temperature is above 5°C (41°F). Part #28002 provides an objective confirmation of both conditions.
When should Method B be used instead of Method A?
Method B is advisable when: welding is performed at low heat input (e.g. GTAW root pass on thin-wall pipe), ambient temperature is below 5°C (41°F), the joint has high restraint (heavy flange, T-joint), or the steel has a CET above 0.45. Method A gives a conservative — safe but sometimes higher than necessary — preheat result. In practice, many site WPS documents use Method A and accept the conservative margin rather than calculating heat input for every pass.
Need Tempilstik® for a project working to EN 1011-2 or AWS D1.1? Fast Group (tempil.vn) is the authorised Tempil® distributor in Vietnam — genuine product with C/O, C/Q, and VAT invoice. Free part number selection support based on your WPS.
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