Management at Majuba power station ‘was aware of vibrations’

2014-11-04 00:00

THE management of the Majuba power station has known since January that the central coal silo was vibrating and the concrete structure was showing signs of stress.

Eskom workers who are members of the union Solidarity reported professional consultants had even attached equipment to the silo to monitor the vibrations and resonance in the silo.

“By June and July this year the monitoring equipment showed there were vibratons in the structure every 30 seconds.

“At that stage you could already see the cracks where the silo started leaking coal on Saturday and then collapsed,” the head of energy at Solidarity, Deon Reyneke, told sister paper Beeld yesterday.

“Three weeks ago the monitoring equipment showed that the vibrations had increased so that interruptions between vibrations were only of three to five seconds’ duration.

“This was common knowledge among people who worked in the area of the silo — at that stage people started to refuse to go near it,” Reyneke said.

The silo started leaking coal near the cracks on Saturday at about noon. It collapsed about 40 minutes later, cutting the coal supply to the power station’s six units.

This information from Solidarity agrees with information which Beeld had received from consultants, who indicated the management of Majuba had been told since last year that the maintenance work on the coal silos was not up to standard.

The consultants, who want to remain anonymous, had asked to investigate the coal silos at Majuba, but were refused permission.

A structural engineer who has done a lot of work for Eskom said the cracks in the silo could have been repaired even as late as June or July, when the cracks were first spotted.

“Vibrations and resonance in any concrete structure are serious signs of stress and decay.

“This happens when the strengthening steel inside the concrete starts to corrode because moisture is reaching it.”

He explained the volume of steel increases by about 300% when it rusts.

This increases the load inside the concrete incrementally, which is what causes the concrete to crack. There are standard methods in place to repair such cases.

“The silo must be emptied and the concrete must be chipped off around the cracks to expose all the corrosion on the reinforcing steel.

“The steel then gets treated with a chemical product to stop the rust and the concrete is replaced by a filler product to waterproof that area again,” he said.

He said if the cracks are serious, it is even possible to add a “belt” around the silo to strenghten and safeguard the structure.”

He said corrosion was a constant danger in coal silos because the coal contains sulphur, which acts as a catalyst for oxidation of steel.

“And if the coal is wet, as is often the case these days in Eskom’s power stations, corrosion is a serious risk which must be constantly monitored,” the engineer said.

Eskom’s communications manager Raeesa Waja last night said Eskom is aware of the allegations made by Solidarity.

“The executive committee is looking at it. We will react later,” he said.

Acting head of technology at Eskom, Matshela Koko, said on Sunday the silos were inspected in September last year. He said the cause of the collapse was as yet unknown, but it was definitely not because of a lack of maintenance.

A video recording was made while the silo collapsed.

Eskom was willing to make the video available to the media and public on Sunday, but Eskom’s liaison office asked that the video be issued only yesterday to accomodate logistical issues. But yesterday Eskom simply refused to release the video.

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