Reports have been published in various newspapers about cracks in the bedplates of Sulzer RTA84T and RTA84T-B low-speed marine diesel engines. Some reports have tended to be rather alarmist, exaggerating the extent and severity of the problem. For this reason, Wärtsilä NSD Corporation and HSD Engine Co Ltd, on behalf of Hanjung (KHIC), have jointly issued a report to put on record the basic facts and briefly describe the problem.
There are today 41 of the RTA84T and RTA84T-B engine types in service, all in VLCCs. The first began operation in 1994, and the longest running engines have individually accumulated up to more than 40,000 running hours. Of these, 11 engines have cracks in one or more of their bearing girders. The bearing girders are arranged transversely in the engine bedplate and carry the main bearings in which the crankshaft runs. The cracks are all in the circumferential direction beneath the bearing housings.
Two remedies have been developed, involving the weld repair of cracks and replacement of bearing girders, both being made in situ. However, a complete change of bedplate appears to be preferred by most of the shipowners concerned. The time required for repair is expected to be about two months, and will in most cases be combined with normal dry-docking of the ships concerned.Meanwhile, the engines are safe to operate as most of the existing cracks are stable and not propagating, or in a few cases only propagating very slowly. The existing cracks are carefully monitored and unaffected girders are regularly checked for cracks.
For future new engines, in order to restore confidence in view of the on-going newbuilding projects, a new bearing girder design has been introduced. This modified girder design has a thickness of 60 mm to increase the tolerance for material deficiencies, and an extra manufacturing specification regarding casting risers. In addition, it has been agreed with licensees to exert a stricter quality assurance procedure and to adopt an improved quality and test specification.
Wärtsilä NSD summarised their findings stating “It is clear that all requested answers are not yet available but it is also a fact that there is no technical need to take immediate unplanned action to replace bedplates or to replace cracked girders on engines. Such engines can clearly remain in service as normal. It is also a firm opinion of Wärtsilä NSD that Sulzer RTA84T and RTA84T-B engines, which do not have cracks, even if fitted with 'type b' girders, can continue to operate without any other action than visual inspection of the girders at prescribed intervals.”