This paper summarizes the results of a series of demonstrations used to evaluate the effect of various conditions on conventional automated full-length ultrasonic inspection of heavy wall tubular goods using reference indicators with depths significantly less than 5% of the specified wall thickness.
Nondestructive examinations are relied upon to know the quality of pipe used to perform great tasks. Ultrasonic inspections are the Industry's most reliable and critical examination currently being performed on Oil Country Tubular Goods. The minimum defects searched for are 5% of the specified wall thickness. For example 9 5/8? casing weighing 53.50 pounds per foot with a specified 0.545? wall thickness would be inspected with 0.027? (5%) deep reference notches normally 1? in length. When considering string designs for wells with high pressures and high temperatures, the wall thicknesses required are over 1.000?, which is double the typical API specified size. When using the API recommended notch depth of 5% for critical applications in thicker wall pipe known stress risers could be allowed. The past has shown failures could occur with flaw depths as little as 0.025? regardless of the specified wall thickness they propagate in. This does provide a greater inspection challenge for High Pressure High Temperature wells.
This study was performed with an array of multiple transducers applying the ultrasonic inspection technique. Each tube is scanned full length on the outside diameter surface in the longitudinal and transverse orientations.