Following the recent failure of two gas-fired power station steel chimneys, Zenith would like to immediately bring to the attention of steel chimney owners our findings and recommendations to assist in identifying, analysing and refurbishing the areas of steel chimneys which may be particularly prone to high corrosion. Of particular note, we will be focusing on two main issues, which will be applicable if you have steel chimneys, namely, chimney dampers and corrosion under insulation.

When it comes to the inspection, structural analysis, specialist access, repair and maintenance of industrial chimneys, Zenith is the leading industry specialist in the country with a world class in-house engineering team combined with highly qualified site operatives.

In the 1990’s more than thirty gas-fired power stations were constructed in the United Kingdom by the newly privatised electricity industry. This was brought about by a regulatory change that allowed gas to be used as a fuel for electricity generation, the faster return on investment of gas-fired stations which are quicker to build than coal-fired stations, and the development of more efficient combined cycle gas turbine technology. Almost all these stations were constructed with steel chimneys ranging in heights of between 60 m to 70 m and having diameters of up to 6 m.

The change in chimney construction was brought about by the economy of steel chimneys coupled with developments in chimney damper technology which allowed larger steel chimneys to be safely designed.

Steel chimneys are much more at risk from the effects of across-wind oscillations caused by vortex shedding due to the inherently low damping of steel as a material and the development of dampers overcame this problem.

Steel chimneys on plants other than gas-fired power stations may be equally at risk, although generally they are smaller in diameter.

There are two significant factors that have come to light with the recent failures: firstly, the often very localised nature of corrosion which may not be picked up in routine surveys and secondly the risk presented by deterioration in the performance of the damper units – which are essential to the safety of the chimneys – and the need to monitor that performance.

For the safe operation of steel chimneys, it must be ensured that the plate thicknesses in all areas are still within the design thickness and that the damper units are operating correctly.

Zenith personnel have recently been involved in the refurbishment of several steel chimneys and the dismantling of a partially collapsed chimney and have seen at first hand the challenges facing owners of aging steel chimneys. Industry guidelines for steel chimney inspections recommend annual ultrasonic thickness measurements without specifying a frequency, and these may typically be taken on a 1m grid. However, this will not pick up local high corrosion, particularly that which occurs externally under insulation. On several projects recently Zenith has used a scanning machine which can automatically scan up to a 600mm wide band over the height or circumference of the stack and provides a much more comprehensive survey. In the process they have gained knowledge as to the areas which may be particularly prone to high corrosion.

Dampers – where fitted are critical to the safety of the stack and regular inspection and maintenance is essential. Zenith personnel have been involved in damper maintenance and replacement on several chimneys.

Zenith has a global reputation for innovation and excellence. Our in-house world class team of engineers oversee the inspection and full structural assessment of steel chimneys. We have an unrivalled level of experience and constantly bring industry leading access and repair solutions for the world’s foremost blue chip companies in the oil, gas, petrochemical, cement and power industries.

Please view below our recently completed safe dismantling of a steel chimney at a gas-fired power station in the United Kingdom following the chimney’s failure during the month of December 2024.