IDENTIFICATION OF ULTRASONIC ECHO SOURCE IN 4140 STEEL BARS USED FOR AN OIL-FIELD TOOL

Ultrasonic reflections obtained in inspections of 4140 round steel bar s being manufactured into oilfield tools were not associated by the ma nufacturer with any easily identified anomaly within the material. One of the bars was selected for more detailed analysis. A detailed secti oning procedure was initiated in order to isolate the source of the re flections. Using both angle beam and longitudinal beam probes, reflect ions were confirmed in smaller pieces cut from the bar. An attempt to correlate the reflections with cracks in the material was unsuccessful . It became clear in the course of the investigation that the indicati ons were originating within a region where the attenuation was higher than expected. After the presence of significant cracking in the mater ial was eliminated, extensive metallurgical investigations showed that the region of the material which exhibited the high attenuation, and was the source of the reflections, also possessed a higher than expect ed density of nonmetallic inclusions in the form of manganese sulfide stringers. Comparisons with other regions in the bar showed the densit y of the inclusions to be higher in the region that was the source of the reflections. While the correlation of the reflections and the incl usions is only circumstantial, the association is felt to be quite str ong.