On-board gearbox inspection on container vessel sailing from Taiwan to Hong Kong

Challenge

Our customer invited Stork diagnostic services to carry out a visual inspection of two renk-tacke PTG 16 epicyclic gearboxes. The gearboxes are part of the power supply installation on a container vessel and are driven by tow gas turbines.The crew discovered  excessive clearance at the low-speed shaft of the gearboxes. In order to determine the condition of the gearboxes, we performed a visual inspection of the gearboxes , including flanks and bearings. 

The equipment involved is a steam turbine-driven generator set. It is also possible, if desired, to supplement this with two gas turbines in order to obtain more power from the generator. These two gas turbines drive a David Brown parallel gearbox by means of two planetary gearboxes. The parallel gearbox’s output shaft is linked to the generator.

Solution

The engineers on the container vessel have noticed excessive bearing clearance on the planetary gearbox’s ouput shaft during an alignment. Based on their observations, Stork Diagnostic Services has been asked to inspect the gas turbine-driven Renk Tacke planetary gearboxes for defects and/or damage to bearings and/or gearwheels.

An Everest XLGO-type videoscope from General Electric was used during this visual inspection to allow for closer scrutiny of the bearings and the planetary area of the gearbox.

During inspection severe bearing damage was found on both bearings of the low speed shafts of both gearboxes. The bearing damage consisted of indentations, standstill marks and corrosion. Micropitting has been formed on the inner race and on the rolling elements. 

The flanks of the sun wheels, planet wheels and ring gears showed corrosion, indentations and scratches ( usually caused by hard particles in the lubrication). Corrosion has been observed on the planet wheel carrier and on the inside of the gearbox casing.

The recommendation was to have the two gas turbine-driven planetary gearboxes extracted and overhauled. Our customer will consult internally to determine the fate of the gas turbine area of the equipment, as to whether it will be overhauled or removed from the vessel as enough power can be generated from the steam turbine alone. To avoid corrosion and standstill damage, it is recommended to reduce the moisture content in the gearbox and minimise standstill of the equipment.

Benefit

Gearbox damage examples- view pictures below from ge everest xlgo videoscope  corrosion, scratches, micro-pitting, stillstand marks and indentations

Bearing damage at the low speed shaft with indentations, corrosion and standstill marks.

Gearbox 1: The sun wheel (picture 1), active flank shows signs of increased contact pressure and scratches. The planet wheel shows scratches, minor indentations and corrosion at the active flank (picture 2) and inactive flank (picture 3).

Gearbox 2: The planet wheel (picture 1) shows micropitting, indentations and corrosion. Also micropitting and scratches on the active flank of the sun gear (picture 2), corrosion at the inactive flank (picture 3).​

Location: Container vessel sailing from Kaoshiung, Taiwan to Hong Kong.

Market segment: Maritime, marine, container vessels

Gearbox details: The epicyclic gearboxes - Renk Tacke PTG 16 - are part of the power supply installaton on a container vessel and are driven by tow gas turbines.

• Generator: Siemens 4080 kW

• Gearbox manufacturer: Renk Tacke (planetary)

• Power: 1140 kW

• Input speed: 25000 rpm

• Ratio: 13,75

• Number of gearboxes: 2