SEVERE OIL LEAKAGE THROUGH BEARING PADESTAL 33MW TG. UNIT-1. BORL, BINA PROJECT

OIL GUARD RING ASSEMBLY

DESCRIPTION During steam rolling and synchronization of U#1 from 22.07.10 to 29.07.10, severe oil leakage was observed from rear brg pedestal end (TE). The leakage started when turbine reached at full speed i.e 5000 rpm and gradually increased. The pedestal end from where oil was leaking out is located very close to turbine exhaust casing.

During that time U#2 pedestal box up work was in progress During that time U#2 pedestal box up work was in progress. It was seen that with rotor in position, the oil guard ring was coming in direct contact with the oil deflector collar of the rotor. As per drg there should be an axial clearance of 4.0 mm clearance between rotor and oil guard ring. It was suspected that similar condition must be existing in Unit-1 also.

ACTION TAKEN Pedestal was opened for inspection. Severe rubbing marks on the oil guard ring was observed. The oil guard ring was machined on the face. One of the brass sealing fins had to be sacrificed in order to obtain adequate clearance . The component was assembled and 4.0mm clearance was ensured. The oil leakage problem was resolved.

ANALYSIS The turbine was assembled and tested at Hyderabad works with all the components supplied to site. During erection, TG axis and pedestal locations were finalized as per drg. All clearances of turbine internals were rechecked and recorded during box up except this reading.

OIL GUARD RING ASSLY WITH ROTOR

The turbine rotor expands by about 4 mm at coupling end. During the course of its expansion it came in direct contact with the oil guard as there was insufficient clearance between them. This caused axial rubbing of the component and also leakage of oil.

REMARKS The oil guard is assembled in the final stage of erection during box up of pedestal. Though this an important component, normally it does not receive proper attention which lead to such mistakes. Assembly of oil guard ring should be paid special attention in view of the rotor expansion issue involved with it.