ARI utilise an innovative Ultrasonic Inspection technique to test Ball Studs in situ from the bottom to improve the time it takes to test each ball stud while still providing a very high Probability of Detection (POD). Below is a description of the qualification of this test procedure.

Ultrasonic testing of Cat® ridged dump truck ball studs from the inferior position of the stud

In the event of a cracked ball stud, serious accidents can occur as well as very costly losses in service. Manufacturers require that they are tested ultrasonically every 1000 hours of service. Guidelines prescribe that they are tested from the top position which requires two technicians and 1.5 hours per truck to test including access time to expose the top of the ball stud. Some technicians test from the bottom (inferior) end to reduce the time (0.25 hours per truck) required for testing however, the accuracy of the assessment is questionable. 

Aims:

1) To determine the accuracy of testing ball studs in dump trucks from the bottom versus top position ultrasonically using usual methods and non-custom/conventional equipment.

2) Should the accuracy of testing from the bottom position using usual methods not meet satisfactory standards, design a method of testing ultrasonically from the bottom position which meets accuracy standards.

Method:

A sample of 10 ball studs from Cat® Ridged Dump Trucks was tested ultrasonically inferiorly (bottom) and superiorly (top) using conventional ultrasonic equipment by two ISO 17025 Ultrasonic Level 2 certified technicians. They were blinded to the condition of the components. Top and bottom testing was done a week apart so technicians could not compare results for each item. The ball studs were then tested using magnetic particle testing to confirm if cracks are present or not. As the results indicated unsatisfactory accuracy for testing ball studs from the bottom using standard technique, a new procedure using a custom-made angled wedge with a 13mm ultrasound probe was developed and tested, with technicians testing the 10 samples using this technique and comparing them to magnetic particle testing results. Technicians were again blinded to the condition of components.

Results:

Testing as per the manufacturer recommended top position versus magnetic particle testing, true positives were 100% and true negatives 100%. When testing from the bottom with a standard probe true positives were 40% when compared to magnetic particle testing, therefore indicating 60% false negatives. Testing from the bottom and using a custom-made angled wedge with a 13mm probe the true positive rate was 80% with a 0% false positive rate.

Discussion:

Testing from the top with a standard probe and from the bottom using a custom angled wedge with a 13mm probe meets satisfactory accuracy standards. Testing from the bottom with a standard probe does not meet satisfactory accuracy values. Given that the time taken to test the ball studs in one truck from the top position versus the bottom position is 1.5 hours compared to 0.25 hours, the results for this new technique suggest using a custom angled wedge and 13mm probe is a satisfactory and efficient alternative.

Read the full article Qualification of Ultrasonic testing of Cat® ridged dump trucks ball studs from the inferior position of the stud as published in Industrial Eye – The Official Journal of the Australian Institute of Non-Destructive Testing