Ultrasonic measuring process for the wall thickness curve of a w

Details Ultrasonic measuring process for the wall thickness curve of a w Ultrasonic measuring process for the wall thickness curve of a w

1993-09-23

1996-12-10

Chilcot, Richard

Measuring and testing

Vibration

By mechanical waves

73588, G01N 2904

Patent

active

055832920

DESCRIPTION:

BRIEF SUMMARY
The invention pertains to an ultrasonic measuring process for the wall thickness curve of a weld seam of a pipe, especially a pipe with a shaved weld seam, wherein an ultrasonic oscillator is coupled acoustically to the pipe via a hydraulic buffer, from it ultrasonic impulses enter in an acoustic entry zone into the pipe, the reflected components of these pulses from the ultrasonic oscillator are received again and fed as an electrical signal to a measured value processing circuit, the ultrasonic oscillator is moved relative to the pipe parallel to the pipe axis and the acoustic entry zone is moved back and forth transversely to the pipe axis in such a way that the weld seam and the peripheral regions to the left and right of the weld seam are passed over; the invention also pertains to devices for execution of this measurement process.
In a welded pipe, the wall thickness curve in the region of the weld seam generally deviates from the curve of the wall thickness of the remaining cross section of the pipe. The goal in the production of a welded pipe is that the wall thickness curve differ as little as possible, preferably not at all, from the wall thickness curve outside of the weld seam so that the welded pipe differs as little as possible from an ideal cylindrical pipe.
Without reworking, the weld seam is generally thicker than the wall thickness of the coil from which the pipe is manufactured. In this process it is attempted to have the weld seam protruding both to the outside and to the inside relative to ideal cylinder geometry, i.e. to be convex. The weld seam can be taken down by reworking, especially shaving, to such an extent that the ideal cylindrical curve is present on the outside and the inside.
During welding, defects may appear; despite the greater wall thickness in the region of the weld seam, the outside contour may run concavely, the inner contour will then have a relatively strong convex curvature. Furthermore, small irregularities in the longitudinal direction of the weld seam, e.g., waves or ribs, may appear.
As a result of the secondary treatment which is summarized in the following under the concept of shaving, material is removed on the outside and inside with the purpose of configuring the cross-sectional curve in such a way that an ideal purely cylindrical pipe geometry is present. The shaving is generally performed with a chisel: an external chisel is used for outside shaving and an internal chisel is used for inside shaving. Both are arranged at a certain distance behind the welding device of a conventional type and need not be discussed further here. If deviations appear during the shaving, e.g., if the attitude of the chisel changes, the chisel wears down or breaks, the pipe geometry will deviate from the sought ideal curve. Typical in such case are shaving operations which are conducted a little above the actual ideal pipe contour and result in sharp edged "steps" in the cross-sectional curve of the pipe. Another deviation involves shaving off too much, causing the pipe then to be flattened out in the cross-sectional curve at the weld seam.
A weld seam test of the type mentioned initially is known which operates by means of a hydraulic-coupled ultrasonic oscillator. This ultrasonic measurement process, however, does not operate with the accuracy required for testing of reworked weld seams. Thus it is difficult to register the geometries of shaved pipes in which the wall thickness in the curve of the weld seam although just as large as that beside the weld seam, nevertheless deviates from the ideal curve of cylindrical geometry, because the outside shaving, for example, has caused flattening and a certain convexity was preserved during the inside shaving. But in particular, according to the previously known ultrasonic measurement procedures, steps, especially small steps in the cross-sectional curve of the pipe cannot be demonstrated with certainty. The transportation of the pipe by the conveyer mechanism always takes place with a certain irregularity. The pipe being conveyed

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