Refurbishment of four ID (centrifugal) Fans that were first installed 40 years ago

Sheffield (UK) is home to the SMACC (Stainless Melting and Continuous Casting Plant), Wire Rod Mill – ASR (Alloy Steel Rods) and the Bar Finishing Facility – SSB (Sheffield Stainless Bar).

Outokumpu produced the world’s first martensitic stainless steel in Sheffield, more than 100 years ago. The Sheffield plant delivers premium quality, industry leading technical services and tailored solutions, which position Sheffield in a class of its own.

The challenge

Outokumpu has four Howden induced draught fans installed at the melting shop plant that are used within their steel making process. The fans which were originally installed in 1979, operate at a temperature of up to 80-90°C. The fans are 6.4m long by 2.6m diameter and weigh a total of 11.5 tonnes.

Since their installation 40 years ago, remedial repair work has been carried out on each of the fans. However, due to excessive wear on the impellers it was identified that a major repair refurbishment was required to bring the impellors back to operational standard. A four-year program was developed to address this refurbishment requirement, where a fan impellor unit would be removed sequentially on a yearly basis to carry out the work.

Through a vigorous tendering and evaluation process, Howden was commissioned to carry out some of the refurbishments requirements.

Our solution

Following a detailed examination of the removed fan unit, this investigation identified some extreme wear of the main impellor components. After many years of ongoing repair work to the impeller it was recommended that to provide a cost-effective solution the centre plates and main impellor blades would need to be replaced with the remaining components of the impeller repaired, the existing side sheets and hub were to be re-used.

In addition to the refurbishment, Outokumpu specified that the refurbished impellor had to deliver operational reliability and cost effectiveness during its lifecycle. It was also required that only minimal and minor repairs works should be undertaken during its four-year life cycle. This challenged Howden to optimise wear resistant materials and best available technology in the construction of the impellor particularly the most exposed wear areas.

Following reconstruction, the impeller was re-balanced and after detailed analysis the main impellor shaft was reused and replaced into the assembly. This refurbishment was the most cost-effective solution for the client as opposed to supplying a new impeller and shaft assembly.

Following refurbishment of the impellor unit, Howden’s Site Service division were commissioned to carry out the change of the impeller and install the refurbished unit, all within Outokumpu’s tight operational outage periods.

Howden were able to refurbish the impeller safely, within a very tight lead-time and achieved an on-time delivery of this order all within the client’s pre-arranged outage dates which ensured they had no major interruptions to their product production.