SHE Alert No. REN-WIN-ON-SHE-COM-2021-001
Introduction
The maintenance requirements contained in the Avanti User’s Maintenance and Installation Manual for the Avanti Service Lift, SWP installed in the Siemens WTG and Dolphin installed in Vestas WTG, details the inspection frequency and maintenance workscope. The Service Lift is designed for standard operation until an overhaul at 20 years or 250 hours of operation (whatever occurs first).
During 2020 Avanti issued a letter detailing a deeper (or enhanced) inspection maintenance plan in addition to the requirement prescribed in the manuals supplied with the turbine. The deeper inspections are completed on the traction hoist unit and the fall arrest safety device in addition to the original annual maintenance workscope.
Avanti’s recommendation is to introduce deeper inspections on year 10 or at 125 hrs (whatever occurs first), or earlier if all previous maintenance records, inspections or service history are not complete.
Background
What happened?
SSE currently complete annual maintenance as prescribed in the User’s Maintenance and Installation Manual using a competent contractor, Statutory Inspections are completed annually, as per SSE’s written scheme of examination, and pre-use inspections and checks are completed prior to first operation each day.
In response to the Avanti deeper inspection plan and as a confidence assurance check, SSE commenced a sample of deeper inspections at site on Service Lift’s installed in the Siemens 2.3VS WTG which are in their 9th year of operation and working hours range from 55 to 75hrs.
During these inspections 100% of the original traction hoist units have demonstrated substantial levels of wear on the key and keyway of the hoist motor shaft, and the gearbox shaft. These units were subsequently declared unserviceable by Alimak, the service function and group owner of Avanti.
Following the discovery of this defect SSE and SGRE inspected 3 further traction hoist units at another SSE site with working hours ranging from 50 to 80 hrs, averaging 63 hours and 9 years of service. 100% of these units also failed due to wear in the aforementioned keys and keyways.
This connection is not inspected during the current annual maintenance, nor is it possible to detect or inspect for this issue during Statutory Inspections and so would remain undetected until a deeper inspection was conducted.
The centrifugal brake forms part of the coupling assembly on this keyed connection. Dependant on the failure mode, it is possible that the key will shear and none of the units brakes will operate as designed. In such an event the Service Lift would be uncontrolled and reliant on the fall arrest safety device to arrest any descent. The fall arrest safety device is the last form of defence in the event of an uncontrolled descent of a Service Lift.
As a result of the above findings SSE have removed all Avanti Service Lifts fitted with an Avanti M500 (500 and 508) Series traction hoist unit from operation, as it is not possible to determine when the wear present exceeds the manufacturing tolerance of 0.056mm as confirmed by Avanti.
These findings are now under further investigation and any relevant learning points will be communicated when available.
Actions required
In line with SSE’s commitment to Safety, all Avanti Service Lifts fitted with Avanti M500 (500 and 508) Series traction hoist units have been removed from service. This Safety Alert will be reviewed and amended as the investigation progresses.
Discussions have commenced with the Turbine OEM and Service Lift OEM to investigate the findings, establish wear limits and remedial actions required.
Further Information
These findings are now under further investigation and any relevant learning points will be communicated when available.
General Note
Acknowledgement: This information was provided by SSE and shared with SafetyOn for circulation to members