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Solvator Award 2021 for „Weld Repair of Cast Iron Steam Turbine Casings”

2022-07-14 | 

A groundbreaking success was achieved by voestalpine Böhler Welding UK for its his customer "RWE Generation UK"

The challenge was to find a solution for problems with the steam turbine casings for CCGT power stations, made out of GGG40 grade cast iron. voestalpine Böhler Welding UK's world-class expertise helped to offer precisely the welding consumables needed to increase productivity and speed of repairs within the short timeframe available for work during the shutdown.

With a height of around seven meters, a width of four meters and a typical wall thickness of 40mm the turbine castings are extremely large. They suffer from erosion by water drops, which have a different depth of wear pattern.

Here, typical repairs are required in some places to a depth of 20 mm. Our expertise in cast iron repair was in demand", explains Stuart Thomas, voestalpine Böhler Welding UK.

The task was to investigate different welding processes and techniques for repairs to GGG40 cast iron. To make matters more difficult, the repairs had to be carried out within a short period of time during the power plant shutdown, within the framework of 2 weeks.

Stuart Thomas fleshes out the challenges as follows

"The task was to carry out repairs on a huge section of cast iron without cracking the weld metal or the base metal or the heat-affected zone. And the most effective welding processes had to be used, allowing welding in all positions and in hard-to-reach places."

At the start of the project, Stuart Thomas and RWE held a global conference call, which was also attended by colleagues from UTP MAINTENANCE, Stefan Otto and Jean-Pierre Van Nieuwenhoven. The team of experts presented and discussed the basics of cast welding and informed RWE of the best practices to follow for successful cast repair. Several products were selected for further discussion and welding trials: UTP 86FN / UTP A8051Ti / SK & UTP HYDROCAV / SK FNM4-G / SK FNM-G / CN 13-4 PW-FD.

Consumables where chosen based on application advice and best availability. Gary Taylor and Stuart Thomas from voestalpine Böhler Welding UK visited RWE with TEI (the fabricator) to make an initial assessment of the weldability of the selected consumables. voestalpine Böhler Welding UK assisted in the selection of the optimum welding parameters and techniques to achieve optimum weldability combined with best practice to reduce HAZ hardness.

How did the best solution come about?

After the initial weldability tests, more samples of the selected products were ordered, as well as alternative diameters for further weldability tests. After further tests at RWE, the products UTP 86FN (2.5 mm and 3.2 mm) and UTP A8051Ti x 1.2 mm and UTP A8051Ti x 2.4 mm x 1000 mm were selected. RWE conducted further weldability tests and modifications to the welding procedure protocol to find the fastest welding technique that gave the lowest HAZ hardness with low defects and good mechanical properties.

The welding procedures were qualified with low heat input, acceptable melting values, good mechanical properties and in a range of welding positions. The qualified welding procedures were then used during shutdowns at the Pembroke power station.

RWE now has a proven solution to safely and quickly repair the damage caused by water drop erosion in the steam turbine casing. Water drop erosion is a permanent problem, so the solution will continue to be used where this type of erosion occurs.

Trust counts

Once more, RWE was utterly convinced by the fast, efficient and solution-orientated approach by voestalpine Böhler Welding UK who offers a special kind of services and products of outstanding quality.

About Rewe Generation UK

Since the closure of its last coal-fired power station in the UK in March 2020 (Aberthaw), RWE has continued to provide firm, flexible thermal gas-fired generation with around 7,000 MW of modern and efficient operational capacity, including at the state-of-the-art Kings Lynn CCGT. RWE generates over 12% of all electricity in the UK, of which around 10% is from the gas fleet alone.