Comparison of results of magnetic and ultrasonic flaw detection in a gas pipeline subjected to corrosion cracking

We compared the results of diagnostics of the state of an overland underground gas pipeline carried out by flaw detection inside the pipe with the aid of a flaw detector UltraScan - CD made by Pipetronics, and also by subsequent local diagnostics of detected defects by methods of magnetic flaw detection in dug pits, by laboratory flaw detection of cut-out sections with defects, and by their metallographic investigation. The methods were compared according to known dimensional characteristics of the defects obtained in the investigation, and also according to the results of theoretical evaluations of the residual life of the section containing cracks. It was concluded that the method of ultrasonic flaw detection inside pipes can be used for evaluating the state of overland underground gas pipelines subjected to corrosion cracking, and for determining the theoretical residual life of the damaged places without additional digging of pits. The residual life calculated from data of flaw detection inside pipes is in all cases too short (on an average by 34%), which constitutes an additional safety margin.