Attemperator Fabrication for a Lincolnshire Power Station — Cr-Mo Steel in ASME Service
The Client
GC Logicals was approached by a leading ISO 9001 certified fabrication and welding company who had secured an order to supply a number of Attemperators into a power station in Lincolnshire. The fabrication scope was, on the face of it, straightforward. What lay beneath the surface was anything but.
A Note On This Project
This case study is included deliberately — not because it was the most complex fabrication GC Logicals has been involved in, but because it illustrates something more important than complexity.
When the client made their approach, GC Logicals was transparent from the outset: the specific material grades involved were outside familiar territory. The client’s response was unequivocal — they wanted GC Logicals involved precisely because they trusted the approach, the methodology, and the commitment to getting it right. That trust was not misplaced.
What followed was a disciplined exercise in working through unfamiliar technical territory systematically — consulting the correct codes, verifying every requirement, and ensuring that a job that looked simple on the surface was treated with the rigour it actually demanded. It remains one of the most satisfying projects GC Logicals has delivered. Not because of what it looked like, but because of what it could have been without the right oversight.
The Scope
An Attemperator is a device used in power generation to control steam temperature — typically a pipe assembly incorporating a branch that introduces atomised water into the main run to reduce steam temperature to the required level. The fabrication itself was relatively straightforward: a main run pipe of 4,500mm length with a branch pipe assembly.
The complexity was entirely in the materials.
The Challenge
Main Run Pipe — 13CrMo4-5, 25mm Wall
The main run pipe and associated internals were specified in 13CrMo4-5 — a Low Alloy Chromium Molybdenum steel offering good creep resistance in pressure service at elevated temperatures. The wall thickness was 25mm. Critically, 13CrMo4-5 is a European designation — and the item was being welded to ASME requirements. Identifying the correct ASME equivalent material was not optional; it was the foundation on which every subsequent welding decision depended.
Through code research and technical library review, GC Logicals identified the nearest ASTM equivalent as ASTM A182 Grade F11 — classified under ASME IX Table QW-422 as P Number 4, Group 1.
Branch Pipe and Inserts — ASTM A182 Grade F22
The branch pipe and all inserts were specified in ASTM A182 Grade F22 — a higher-grade Chromium Molybdenum material with significantly improved creep strength, capable of sustained service up to 600°C. This is an ASME designation, classified under ASME IX Table QW-422 as P Number 5a, Group 1.
The combination of two dissimilar Cr-Mo P-number materials — one European-designated, one ASME — across a 25mm wall thickness immediately signalled that existing welding procedures would not be adequate, and that preheat and Post Weld Heat Treatment would be mandatory requirements.
No Existing WPQR Coverage
A full gap analysis of the company’s existing WPQR and WQR confirmed what experience suggested — no suitable qualifications existed to cover these welds. Three new PQRs were required:
- PQR A: P No 5a to P No 5a — ASTM A182 F22 to ASTM A182 F22
- PQR B: P No 4 to P No 4 — ASTM A182 F11 to ASTM A182 F11
- PQR C: P No 4 to P No 5a — ASTM A182 F11 to ASTM A182 F22 (dissimilar)
Preheat, PWHT and Hydrogen Induced Cold Cracking
Both material grades are susceptible to Hydrogen Induced Cold Cracking (HICC) — a serious risk with Cr-Mo steels if thermal management is not correctly controlled. GC Logicals consulted ASME VIII Division 1, specifically:
- Section UW-40 — Procedures for Post Weld Heat Treatment
- Section UCS-56 — Requirements for Post Weld Heat Treatment
The requirements were verified and specified:
- Preheat: 150–200°C applied to all test pieces and production welds
- Controlled cooling: insulation blankets applied immediately after welding to retard the cooling rate and limit HICC risk
- PWHT: 675°C for a minimum of one hour per inch of section thickness, with heating and cooling rates specified in full compliance with ASME VIII Div 1 UCS-56
Welder training was provided to ensure every welder on the job understood the preheat requirement, why it was necessary, and the consequences of non-compliance. This was not a tick-box exercise — it was a genuine technical briefing.
The GC Logicals Approach
Weld Mapping & Procedure Planning
A full weld map was produced to identify every weld type, material combination, and wall thickness across the scope. This drove the three-PQR qualification programme and ensured no weld on the job was left without a fully qualified, code-compliant procedure.
Welder Qualifications
Welder qualification was straightforward — the recommended weld consumables for both material grades were classified as F6 under ASME IX, meaning existing welder qualifications provided coverage without the need for additional qualification testing.
WPQR Qualifications with Tech Inspections Ltd
Tech Inspection Ltd (techinspection.co.uk) — a trusted GC Logicals partner and UKAS accredited Certifying Body and Recognised Third Party Organisation (RTPO) — were engaged to support the qualification programme. Their response was exemplary. All three PQRs were turned around inside three weeks — exceptional performance given the PWHT scheduling, laboratory availability, and testing requirements involved.
Documentation
A full documentation package was submitted for review by both the fabricator and the end client, covering:
- Inspection and Test Plan (Quality Plan)
- MPI Procedure
- Radiography Procedure
- Ultrasonic Testing Procedure
- Welding Documentation Pack
- PWHT Procedure
Every document was returned Code 1 — Approved Without Comment.
Final Manufacturing Record Book (MRB)
On completion, GC Logicals compiled and issued the Final Manufacturing Record Book — containing all drawings, procedures, test reports, material test certifications, and the fully signed-off ITP. A single, complete, auditable record of everything that was done and how.
The Outcome
The Attemperators were manufactured and delivered on time, within budget, and right first time.
The fabricators were skilled, capable, and professional throughout — this was never in doubt. What GC Logicals brought to the project was the technical knowledge to identify what the materials actually demanded, the code literacy to verify every requirement from first principles, the qualification programme to underpin every weld, and the welder training to ensure the shop floor understood what they were being asked to do and why.
A relatively simple fabrication. An outcome that was never in doubt — because the groundwork was done correctly before a single weld was made.
It could have been a very different story.
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