Measurement of pipe joint misalignment at weld interface

Details Measurement of pipe joint misalignment at weld interface Measurement of pipe joint misalignment at weld interface

2000-08-21

2001-08-14

Dunn, Tom (Department: 1725)

Metal fusion bonding

Process

With condition responsive, program, or timing control

C228S103000, C219S124340

Reexamination Certificate

active

06273320

ABSTRACT:

This invention relates to the girth welding of pipes, and, more particularly, to checking the alignment of two lengths of pipes to be welded.
In the construction of some specialty pipelines, it is very important to match the ends of individual pipeline segments at the joints prior to welding. The critical match here is the alignment of the internal pipe wall surfaces. This is a weld area that can significantly impact the weld integrity. In practice, a perfect match is not possible, but specified tolerances must be maintained.
FIG. 1
illustrates this situation, showing a misalignment which is referred to as a Hi Lo. Presently, the match between pipes
1
and
2
is measured by mechanical means such as special Hi Lo gauges, bridging bars, micrometers, and calipers. Though this has been adequate, it is only applicable in applications employing an open gap weld profile. The gap assures access to the internal pipe surface prior to welding as can be seen from FIG.
1
. New girth weld welding processes require a profile with a closed gap between pipes
1
and
2
, as shown in FIG.
2
. In this latter case, it is not possible to access the internal surface by mechanical means, and thus existing techniques cannot be used.
An object of the present invention is to provide a Hi Lo scanning technique which can be used in such processes.
According to the invention, a method of monitoring the alignment of pipes to be welded end to end comprises supporting a reference bar extending generally parallel to, and external of, the pipes so as to span a weld position of which the ends of two pipes are to be welded, performing measurements of perpendicular distance between the bar and each pipe a predetermined distance from the end of each pipe, determining the thickness of the walls of the pipes, determining the slope of the exterior of each pipe with respect to the reference bar, calculating from the slopes the difference between the distances from the bar to the outer surface of each of the two pipes to the weld position, so as to provide a measure of the misalignment of the outer surface of the pipes at the weld position, differencing the wall thicknesses of the pipes to provide a wall thickness difference, and subtracting the wall thickness difference from the misalignment of the external walls of the pipe to determine the misalignment of the inner surfaces of the pipes at the weld position. If the thicknesses of the pipe walls are known, then it may be unnecessary to remeasure these values, but it is preferred to measure pipe thicknesses at multiple distances from the end of each pipe and average the results to obtain average thicknesses for the two pipes. The misalignment measurements may be repeated at successive points around the periphery of the pipes. Preferably, the distance measurements are made of two different distances from the end of each pipe to facilitate determination of the slopes of the pipes.
Further features of the invention will become apparent from the following description with reference to the accompanying drawings


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