Industries
PAUT for Slewing Bearings

MISTRAS Group’s Phased Array Ultrasonic Testing (PAUT) is ideal for rapid and detailed inspection for slewing bearing components on deck cranes, which can be susceptible to major cracking.

Slewing bearings on on-board deck cranes are essential elements of conventional cranes, but as critical parts of major weightlifting, flaws can emerge. These bearings in motor vessel (M/V) ship deck cranes can suffer from fatigue stress, leading to cracking in critical, high stress areas. The top and bottom inner corners of the protruding slewing ring can be specifically susceptible to cracking. MISTRAS’ capabilities allow sensitive areas of the bearings to be reached and defects to be located efficiently.

PAUT Crack Detection Process & Application

MISTRAS Group’s Phased Array Ultrasonic Testing (PAUT)-based technique for early detection of critical fatigue cracks uses specific phased array probes for detection and sizing of cracks in the affected areas. The complex geometry and difficult-to-detect direction of the cracks on cargo ship rotating cranes require a specialized inspection procedure. Prior to testing, MISTRAS will review the drawing to assess testability of any specific bearing.   

While the crane is out of service, inspection is performed from the upper side of the slewing bearing by using a position encoder. The encoder saves the entire inspection and the results can be analyzed and evaluated after the process. The inspection is fast, allowing for up to three cranes having slewing bearing of 2300 mm diameter to be reviewed on one date with limited preparation.

Application Advantages

Being proactive about asset integrity can be the deciding factor in whether operations are unexpectedly halted. Early detection of fatigue cracks promotes responsible crane usage and prevents damages from hurting production down the line. Application advantages of PAUT for slewing bearings include:

• Safe deck crane operations
• Slewing bearing replacement based on inspection
• Permanent encoded inspection records
• No required crane disassembly
• Inspections can take place while sailing
• Fatigue crack growth monitoring & historical tests

Requirements and Site Preparation

Thanks to MISTRAS’ optimized processes, little site preparation is needed prior to inspection. Preparation requirements to conduct the test are:

• Detailed geometry of bearing must be provided to assess if test of the bearing is possible
• Safe access to the upper side of the slewing bearing
• Examination surface must be cleaned of grease
• Sweet water supply must be provided
• Small rotation of crane to inspect entire circumferential bearing length
• Lights in inspection area
• Customer safety requirements on the vessel
• Any legal/regulatory safety requirements

PAUT Data Reporting

After field analysis is completed, the formal inspection report contains the key results and findings operators need. Processed with reliable software, reports are saved and stored for convenient access and retrieval.   

Screenshots of discovered cracks are included to visualize the state of the asset condition. An estimation of the deepest crack found is given. Horizontal and vertical dimensions of cracks are shown to accurately relay the severity of damage. Based on MISTRAS Group’s accessible inspection results, a course of action and necessary maintenance can be determined to solve the defects.