When a Helicoil thread was damaged on a turbine in the Netherlands, HSOS mobilised teams from Germany and the Netherlands to machine a replacement M107.8×6 thread in weld-critical P92 material – completed within 4 working days of first contact.
Background
During maintenance on a turbine in the Netherlands, a Helicoil thread insert was damaged while removing a blanking plug. The existing thread was already a special repair size – M107.8×6 – machined to repair the original M100×6 thread. A further conventional re-thread was not feasible; the situation called for precision CNC machining carried out directly on site.
Material Challenge: P92 Steel
The component is manufactured from P92 (1.4901 / X10CrWMoVNb9-2), a high-alloy martensitic chromium steel widely used in high-temperature steam turbines. Welding this material demands strict controls: defined preheat, interpass temperature limits, and post-weld heat treatment are mandatory to prevent cold cracking and microstructural degradation.
Welding a fixture bracket directly to the component was therefore ruled out.
Engineering Solution
The HSOS teams from Germany and the Netherlands jointly developed a clamping solution that avoided any weld contact with the base material:
- Nut-based attachment: A suitable nut was threaded onto the component. The support structure was then welded to the nut – not to the component itself.
- Custom clamp fixture: A purpose-built clamp was fabricated at short notice to provide the additional rigidity required to hold the CNC machine securely in position.
- Machining: Using a compact portable CNC machine, the damaged M107.8×6 Helicoil bore was precisely re-machined, allowing a new Helicoil insert to be fitted.
Result
The turbine was returned to service on schedule. The entire process – from first contact to completion – was accomplished in 4 working days, including concept development, fixture fabrication, mobilisation, machining, and sign-off.
Summary
This project demonstrates HSOS's capability to deliver precision CNC repairs on metallurgically sensitive materials with non-standard thread dimensions. Close collaboration between the German and Dutch HSOS units enabled a fast, safe, and component-friendly solution – without dismantling the turbine and without any compromise on quality.