Steam strainer failure caused by ‘uncontrolled rotation’

The cause of the steam strainer failure at the steam turbine of the Delimara power station extension has been identified as the uncontrolled rotation of the filter element within its housing.

Enemalta said that this resulted in abrasion and wear on the filter mesh and subsequent structural failure of the strainer. Following this structural failure, parts of the strainer got lodged inside the stop valve, which eventually prevented the valve from closing properly. Furthermore parts of the strainer entered the steam turbine causing impact damage, known as 'foreign object damage'.

In a statement, the corporation said that the final report prepared by contractor BWSC and steam turbine manufacturer Dresser Rand was submitted to Enemalta last Friday.

"After analysis by Enemalta engineers, who deem it to be substantially clear on the root cause of the failure of the steam strainer and of the damage caused to the steam turbine itself, it has been sent for a detailed review by the third party independent consultant DNV KEMA, engaged by Enemalta," the corporation said.

The measures taken by BWSC and Dresser Rand included the replacement of all damaged parts of the steam turbine and combined control and stop valve in order to return it to 'as new' condition.

The steam strainer and its housing have been modified to eliminate any possibility of a reoccurrence.

It is expected that once the detailed review is completed and the report is judged to be satisfactory, Enemalta will give instructions to BWSC to continue with the test programme.

"If the performance tests, which should take 3 days, are successful, the plant should be ready to be taken over before the end of the year," Enemalta confirmed.

These tests will also be monitored by the independent third party consultant, DVM KEMA, engaged by the Corporation.