Liner cracks can seriously affect the operation of your older type engine

In the first of a new series of Case Studies, The Motor Ship reviews the cause, effect and solution to cylinder liner flange failures in older-type engines.

Over the last decade there have been a number of investigated incidents in which failures of medium speed diesel engines have been attributed to partial or complete detachment of a cylinder liner. In a significant proportion of such cases, the post-event analysis has identified problems occurring in the region of the cylinder liner upper flange, either as cracking or, in extreme cases, in a subsequent material failure that has resulted in the entire flange detaching from the main body of the liner.

As a consequence of such problems, in the initial stages the engine may have suffered from jacket water leaks that have led to entablature block distortion. Ultimately, as the conditions worsen, there exists a risk of complete flange detachment, leading to total liner displacement ? the latter resulting in serious engine damage and catastrophic shutdowns.

Following closer analysis and investigation of these incidents, it has been possible to identify three main causes of the initial failures:

l Cylinder liner detonation damage: in which sudden load application to the engine when the ambient air temperature is low has led to circumferential liner cracks adjacent to the liner flange

l Thermal growth/under flange liner radius cracks: in which a vertical crack forms in the liner caused by thermal/mechanical fatigue mechanism

l Excessive liner flange protrusion: in which the liner installation results in poor or incorrect interface with the cylinder head leading to cracks under the flange fillet radius

Detonation Damage

When engines are operated in low ambient air temperatures and in the absence of no-load charge air heating, the charge air manifold temperatures can fall to 8? Centigrade (and below) as the turbocharger input energy is insufficient to provide heated charge air of sufficient temperature at the moment of sudden engine loading ? commonly known as ?Turbo Lag?.

As the engine load is suddenly applied, detonation conditions are likely to occur that can cause very rapid cylinder pressure spikes/rises ? in certain circumstances exceeding the cylinder liner material fatigue limits.

When these conditions exist, then circumferential cylinder liner wall cracks can occur adjacent to the liner flange. Continued engine operation with these cracks present will most likely cause these cracks to propagate causing jacket water leakage into the cylinder and ultimately result in total liner flange detachment and very serious engine damage.

In practice, initial signs of such cracks forming have been evident from gas bubbles collecting in the respective jacket cooling water outlet pipework system.

Thermal Growth

When a medium speed diesel engine operates at a rating in excess of 18 to 19 Bar BMEP, there will be conflicting thermal and mechanical operating conditions present. The thermal growth of the upper section of the cylinder liner cannot be restricted or restrained by the entablature block upper register or the cylinder head to liner flange clamping load.

Continued operation, particularly rapid thermal cycling as often found in ferry operations where ship manoeuvring frequently occurs, can result in deformation of the upper engine entablature block register and cracking below the cylinder liner flange.

In practice, this condition has been widely recognised by the appropriate parties and has been greatly reduced following the introduction of the intensely cooled liner flanges and bore-cooled type cylinder heads. Additionally, shot peening of the upper liner sections has also been reported as substantially reducing the risk of vertical liner flange cracks.

Excessive Protrusion

Where cylinder liners are installed with excessive liner flange protrusion above the upper entablature block face, then direct cylinder head contact with the upper flange fire dam can occur. When this happens, the liner can sustain cracks at the liner?s under-flange fillet radius position.

In practice, this type of failure can be avoided by checking and adjusting the liner flange protrusion to comply with the engine manufacturer?s specification.

By being aware of the above problems, it will be evident that early diagnosis and consultation with the appropriate engine manufacturer will greatly reduce the likelihood of extensive engine damage.