When an Allianz boiler surveyor identified progressive degradation inside the reversal chamber of a horizontal shell and tube boiler at Crediton Dairy, Boiler & Valve Engineering was called in to carry out a technically demanding repair that would restore the boiler's structural integrity and extend its operational life.

The project also underlined Boiler & Valve Engineering’s national reach. From its headquarters in Nairn, Scotland, the steam engineering specialist supported Crediton Dairy in Devon without geography getting in the way of a specialist repair requirement, despite the locations being 600 miles apart. For Crediton Dairy, distance was not a barrier to bringing in the right engineering partner.

The degradation within the boiler had concentrated in the "letterbox" waterside corner sealing welds, where leaching had carved a continuous groove along all four internal corners. Left unresolved, the consequences would have been significant.

Commenting for Boiler & Valve Engineering, managing director Andrew Macdonald says: "This type of repair requires not just technical skill, but a clear and methodical approach to access, preparation and reinstatement. The upper welds are reached through the top manhole, while the lower sections require the careful removal of third-pass plain tubes to fully expose the affected areas."

To carry out the repair, Boiler & Valve Engineering partnered with specialist welder John Varley of Varley Boilers. With weld-procedure access established, engineers extracted the compromised weld material and ground the waterside surfaces clean. Before any welding began, an independent Allianz MPI engineer conducted magnetic particle inspection to confirm all defects had been removed.

Commenting, John Varley says: "The preparation phase is where the quality of the final result is determined. A clean, defect-free surface is what allows the weld to truly restore the boiler's integrity."

Using the MMA welding process, the team reinstated the excavated zones with precision. A second MPI inspection validated the completed welds, confirming structural soundness and compliance. New tubes were then supplied, fitted, expanded and seal welded at both tube plates, completing the mechanical restoration of the boiler internals.

Crediton Dairy’s engineering manager Russell Bennett was clear about what stood out: "The clarity and control shown throughout the repair process was impressive. Every stage was handled with care, and the result speaks for itself."

The project concluded with a full hydraulic test, witnessed and signed off by the Allianz boiler surveyor, providing formal confirmation that the boiler had returned to safe, reliable operating condition.