- since 1996 -
|NDT.net Issue - 2018-03 - NEWS |
|Eccentricity, where the OD and ID of a tube are not concentric, is a problem that is often created during extrusion of the billet before being drawn into a tube. Magnetic Analysis Corporation’s Echomac® ultrasonic test system detects eccentricity at a US copper tube mill that manufactures commercial and industrial grade tube and pipe. Eccentricity in the finished product can mean wall thicknesses that don’t meet specifications, causing problems during further processing downstream.
Ultrasonic transducer probes detecting eccentricity wall variation in 2.125” OD, copper tube with 0.1” wall thickness.
MAC’s Echomac® UT test is applied after the extrusion process, while the tube is being drawn in a high-speed draw-production line, prior to further reduction. The test allows accurate plotting of the actual tube wall thickness and eccentricity over the entire product length. Alarm thresholds can be used to sort material into various quality grades and this data can ultimately be used to make adjustments to the production process.
The Echomac® system uses four transducers spaced 90 degrees around the tube. This allows a very accurate calculation of eccentricity of a non-concentric tube, assuming the external and internal extrusion dies are round. A unique mechanical design is used that allows the transducers to track tube movement off of center. An encoder allows accurate tube tracking and measurement for the Echomac® electronics.
Four Channel Eccentricity testing is a special form of 4 transducer operation that is designed to measure wall variation based on four fixed points, 90 degrees apart. The Echomac® software derives the wall variation from these measurements. Eccentricity is an expression of wall variation but the definition depends on the particular user and their agreement with their customers. For example, 2 or more alarms can be set for different eccentricity sort levels, as set by the customer; 1 alarm for a min-max thickness level, irrespective of the circumferential tube orientation under the fixed transducers; and 1 channel can monitor the average wall. The operator can customize how data is presented. The test system responds only to eccentricity, an attribute of the wall thickness, and Ovality, (OD variation) which may be present, is ignored. All production data is stored and easily retrieved, including product identification, date and stamped time. Eccentricity measurement can be expressed in many forms. The MAC system offers a choice of the many different Eccentricity formula definitions.
Magnetic Analysis Corp.