(i) A-Frame

Cause of Cracking:

• Stress concentration due to sharp changes in section.
• Incorrect preparation of plate edges.
• Welding root faults, like lack of penetration.
• Engine overload or excessive crosshead force.
• Vibrations and twisting.
• Loose tie bolts or termination of horizontal stringers.

Avoidance Measures:

• Use a monoblock structure for the A-frame to provide structural rigidity.
• Avoid sharp changes in section to reduce stress concentration.
• Address manufacturing defects with proper treatment.
• Make the guides integral with the A-frame or manufacture separately from cast iron. Perform regular inspections and checks on tie bolt tightness. Ensure engine operates within specified load, temperature, and pressure limits.

Rectification of Cracks:

• Conduct visual inspections and non-destructive testing (Dye-Penetration Test, Magnetic Particle Test) to locate cracks.
• If necessary, drill and tap the crack to prevent its spread.
• With shore assistance and class approval, remove the crack and repair it with metal welding, using similar or superior material.
• Pre- and post-heat treatments may be required for proper metal integration.

(ii) Bedplate Longitudinal Girder

Cause of Cracking:

• Manufacturing defects such as welding faults.
• Imbalanced engine loads.
• Incorrect tension of fastenings, like holding-down bolts and tie bolts.
• Excessive vibration, which may be due to improper operation of vibration dampers.

Avoidance Measures:

• Ensure constructional strength to provide sufficient rigidity for various forces.
• Prevent sharp changes in section, which can increase stress concentration.
• Eliminate manufacturing defects with proper heat treatments and welding techniques.
• Operate the engine within specified load, temperature, and pressure limits.
• Regularly inspect and maintain all fastenings.

Rectification of Cracks:

• Perform visual and non-destructive testing to locate and assess the extent of the crack.
• Drill and tap the crack if needed to control propagation.
• If shore assistance is available, perform grinding and welding repair under class approval, followed by pre- and post-heat treatments to maintain material integrity.

(iii) Bedplate Transverse Girder

Cause of Cracking:

• Cylinder overload, often from excessive power output, causing high stress.
• Misalignment of the crankshaft, which can lead to uneven loading.
• Material defects and high residual stresses in welded areas.
• Deformation of the tank top due to pressurization or overheating.

Avoidance Measures:

• Build the bedplate with M.S. plates and cast steel cross girders, assembled and welded for longitudinal and transverse strength.
• Reinforce longitudinal strength by constructing bedplate sides as box girders.
• Use cast steel cross girders under the main bearing for transverse strength.
• Place resin cast chocks between the bedplate and tank top to absorb shocks and stresses.

Maintenance and Rectification:

• Perform monthly checks on bolt tension and engine load.
• Regularly measure and maintain crankshaft alignment.
• Check and adjust main bearing jack bolt tension.
• In cases of cracks, follow inspection and repair protocols similar to those for the A-frame and longitudinal girders, including pre- and post-heat treatments where necessary.