Steel Industry Case Study


FURNACE CLADDING

The company produces strip steel for UK and European markets through its pickle line and cold mill. Galvanised coating is also applied through the site’s strip line. The site is capable of producing up to about 2,000,000 tonnes of hot rolled coil per year in a variety of finishes. The installation comprises hot rolling, cold rolling, pickling and galvanising activities.

 

The furnace section of the plant heats the metal strip to 750°C in an oxygen free environment with this temperature held for a given duration to allow the annealing process before being cooled to achieve a temperature of about 460°C prior to entry to the zinc bath coating section. Final mechanical properties are achieved through temper rolling and tension levelling operations prior to passivation/oiling of the product to meet final customer specifications.

 

The company had made significant investments to increase productivity and in order to achieve this, they modified the strip line furnace to increase capacity. The furnace was being used to reduce the section of steel plate for use in the automotive and food sector. 

 

However, there were issues with the internal cladding of the furnace in that it was breaking down regularly due to a change in the heat map of the furnace. The company wanted to run full finish material without any quality defects for their automotive customers. Over a short span of time, there had been 5 production line stoppages, where each stoppage lasted 48 hours resulting in 15 kilo tons of lost production. This equated to approximately £2million in lost contribution as the low-quality steel could only be used in non-automobile applications. There was a 99% probability of the current cladding failing if not rectified.

(Fig 1 - The Plant)

Objective

Fabwell sought to design and develop a new and bespoke cladding for the strip line furnace that would last far longer than the current version (fig 2) i.e. up to 10 years, thus enhancing the service life of the furnace considerably and one which could be easily installed at reduced risk. The aim was to reduce metal scrappage and hence the frequency of plant shutdowns.

(Fig 2 - Old Cladding)

The technological baseline and status at the start of the project

As the cladding was breaking down quite often, it led to high rates of scrappage resulting in large quantities of rolled product being rejected by the company’s customers. When new, the furnace was supplied complete, fully insulated in module form for assembly on site. However, access to the plant and equipment was limited to specific shutdowns which could vary in length depending on customer demand. Once the plant was taken out of service, it could be up to 12 months before review, and any failure would prove costly and inconvenient, thus having a negative effect on the supply chain. With no off-the-shelf solution readily available to address the cladding durability issue, a bespoke programme of development had to be instigated.

Work done

The project began with Fabwell conducting a feasibility study to understand how the furnace functioned as well as its dimensions; the internal surface contours and space constraints; the issues with the current cladding; the method of attachment and material used; the temperature range; as well as the properties and behaviour of materials that could be used of the cladding etc., before a suitable design, development and implementation strategy could be identified (BEIS guidelines paragraphs 27b, 31g and 36).

 

As part of this process, Fabwell trialled a number of different alloys based on the temperature range and desired durability in order to determine which would be best suited for this application, bearing in mind the strict safety measures that the company had already put in place. These included basic 18-8 Ni -Cr stainless steel to more exotic materials. They eventually chose a special hot face cladding nickel alloy 600 & 601 that would be combined with fibre insulation. It was essential that the fibre and cladding were retained independently.

 

Using the knowledge acquired as a foundation and following a critical assessment, a detailed project plan was created to monitor progress and task execution. Fabwell subsequently undertook an iterative design exercise using CAD software, exploring a number of possible configurations for the new cladding and means to secure it to the inner wall of the furnace. CNC programmes were developed as well as exploring machine tool paths, material speeds and feeds in order to determine the most viable approach. In parallel, special jigs and fixtures were designed to support the manufacture.

 

A bespoke fixing arrangement was developed using a combination of welding and screws. Two location points were created in order to retain the insulation and cladding independently. This was to avoid the risk of total failure should the hot face cladding fail. Photos of the new furnace cladding that was developed and installed are shown below.

Failures

There have been no failures to date. All the cladding was inspected during plant downtime and have shown no areas of concern thus far.

Testing

Fabwell engaged an extensive testing process in-house to ensure the new cladding design was compliant with the stringent technical specification and Tata safety standards i.e. with regards to size, weight, fit, form, ease of assembly, durability and dimensional accuracy. The dimensions of the cladding were first verified using a coordinate measuring machine (CMM) followed by assembly testing and quality checks. Further temperature tests were then carried out by the customer at their premises to determine its effectiveness and level of durability (BEIS guidelines paragraphs 27c and 39). Following successful installation, the maintenance costs have been reduced considerably while removing the need for frequent inspections which was the case in the past.