Klaus Wenselowski

One steelworks – Many losses

A number of losses at a blast furnace lead to lengthy and complex repairs and negotiations in the claims settlement process.

Type of industry: Steel manufacture
Age of plant: Over 110 years
Blast furnaces: Three, of which just one active, relined 11 years ago
Production volume: Approx. 1.3 million tonnes of pig iron annually
Blast furnace cooling system: Water, roughly 38,000 l/min
Source: A nearby river
Filter system: Four-stage, initial filtering by coarsely meshed grilles linked to the water source extraction point by means of metal connections

Initial damage caused by dilapidated cooling system

The filter system grilles and connectors corroded over the years. They became brittle and loose and gave way to floating debris that was sucked up by the 1,000-HP pumps. The grilles were deformed, creating gaps through which huge amounts of solids, including many fish, entered the cooling system, which consequently became blocked. In order to ensure proper cooling of the blast furnace, the solids were repeatedly removed and the leaks in the filter stages re-sealed by divers.

Shortly after one such operation, a burst water pipe caused a sudden drop in pressure in the cooling system. Hours passed before the leak was located and sealed. The diminishing water flow rate caused a temperature increase in the blast furnace; cooling elements overheated and melted. Water shot into the blast furnace, and the iron extraction process became unstable. A number of the fans were also severely damaged by overheating.

The policyholder decided to repair the fans and cooling elements during ongoing but reduced operations. The blast furnace went back into full operation about two weeks later. Since it is a very lengthy process to shut down a continuously running blast furnace, the policyholder intended to log the damage to the lining during the general overhaul scheduled to take place five months later.

When the surveyor commissioned by the insurer came to assess the loss, he found that the damaged fans had already been removed and melted down, thus making a detailed loss assessment impossible.

Local temperature increases trigger consequential losses

Just a few weeks later, cracks were discovered in the metal exhaust duct1, so that production had to be stopped for the repair work, which lasted a total of thirteen days. Once again, the surveyor was not informed of the damage until after it had been repaired. The policyholder justified this action by claiming that repairing the blast furnace had priority.

The outcome of the surveyor’s inspection was that the cracks had been caused by local temperature increases due to the ignition of escaping hydrogen. The hydrogen originated from the dissociation of water entering cooling systems which either had not been repaired or had been damaged again. This loss was thus a direct consequence of the initial loss.

Although the operating staff admitted having registered temperature increases of up to 500°F (206°C), they had not investigated their origin. It was not until temperature increases exceeding 1,200°F (approx. 650°C) were measured and the date for the general overhaul was drawing nearer that the decision was taken to carry out repairs. This would have necessitated production stoppages (mostly lasting 12 hours, but sometimes up to 36 hours) which should have commenced shortly thereafter.

Overheating of blast furnace after power outage causes second loss

However, an even more serious incident occurred before the planned repairs could be carried out. It was triggered by a large-scale power outage. Although the plant’s own emergency power generators were initially activated, a 25-Hz generator that powered the cooling-water pumps failed shortly afterwards. Furthermore, the cooling-water valve on the main pump could not be closed, allowing cooling water to flow back out of the blast furnace and into the river. The replacement pump was ineffective because it was at the other end of the plant and was not strong enough.

As a result, the blast furnace overheated. Some of the fans in the lower section of the furnace were so severely damaged that iron ore, coke, cooling water, and solidified and liquid pig iron escaped. The hot substances also set fire to the control systems nearby and damaged the furnace’s loadbearing structures.

The loss was so immense that numerous experts were called in to investigate the loss besides the loss surveyor. Their brief was to establish the cause of the loss, calculate the loss amount, draw up a plan for the quickest possible reconstruction measures, analyse the insurance coverage, and review the possibilities of recourse. Both the insurer and the policyholder commissioned surveyors, resulting in some responsibilities being assigned to several parties.

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