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API REPORT 1114-5 Document Information:
Title
Ultrasonic Testing Requirements for Single-Sided Butt Welds in Offshore Fabrications
American Petroleum Institute
Publication Date:
Jun 1, 1996
Scope:
EXECUTIVE SUMMARY
Background
This project was concerned with investigating alternative ultrasonic
test techniques and alternative acceptance criteria for the
examination of single-sided butt welds. The approach involved
collecting a large volume of ultrasonic test data, covering both
'best' and 'worst' cases, from which the recommendations are drawn.
Objectives
• To evaluate the creeping wave, tandem and time-of-flight
diffraction (TOFD) techniques for the inspection of single-sided butt
welds.
• To formulate prototype ultrasonic test acceptance criteria
which fit into the RP2X framework but apply specifically to
single-sided butt welds.
• To demonstrate, as far as possible, that those acceptance
criteria are effective for the inspection of single-sided butt welds.
Work Undertaken
• Four welded testpieces containing surface breaking and embedded
EDM slots were manufactured.
• A series of ultrasonic detection and classification trials took
place using TWI's P-scan system.
• These data were analysed so that the relative merits of each
technique could be compared and absolute amplitude threshold
information could be extracted.
• A number of recommendations have been made.
Principal Recommendations
• The use of creeping wave and tandem techniques are recommended
only for certain situations such as where there is limited access.
• The use of the TOFD technique is recommended only where speed
of inspection justifies the reduced effectiveness to detect certain
types of flaw.
• A set of alternative acceptance criteria which are recommended
for the examination of single-sided butt welds is given in the report.
Conclusions
1. The use of the creeping wave technique does not improve the
examination of single-sided butt welds for planar surface-breaking
flaws.
2. The use of the tandem technique does improve the examination of
single sided butt welds for embedded planar flaws.
3. The use of the TOFD technique is unlikely to result in as good an
examination of singe-sided butt welds as pulse-echo techniques.
4. The use of automated (pulse-echo) ultrasonic test techniques, where
an image of the weld can be produced, is likely to improve the
examination of the root region of single-sided butt welds.
5. In a 40mm thick, single-sided butt weld, the size of planar flaw
which results in a '50% detection rate' is about 9mm long by between 1
and 2mm high.
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