TWI Industrial Member Report Summary 836/2005
By C R A Schneider, D Kleiner and S M Williams
Pipes clad on the internal or external surface with another material are used in various applications. The ultrasonic inspection of clad pipes presents a significant challenge, because different acoustic velocities in the cladding, the parent pipe material and the weld metal can adversely affect the transmission of ultrasound to and from the cladding. The inspection of clad pipes used in transporting oil and gas through risers in deep-water fields is particularly challenging, where severe fatigue loading and an acidic (sour) environment makes it necessary to be able to detect relatively small flaws.
Differences in acoustic velocities between materials cause partial reflection of the incoming ultrasonic beam at the cladding interface, and refraction and attenuation of the transmitted beam. The amplitude and position of flaw signals may be affected, particularly in the region of weld caps. Also, the nature of the bond between the cladding and weld metal can affect the inspection of welds, particularly of the root.
Theoretical models of inspection systems can, in principle, be used to support the inspection of clad pipes (as well as ultrasonic inspections more generally) by:
- Allowing inspection procedures to be optimised;
- Allowing inspections to be qualified more quickly and cost-effectively by avoiding the need for large numbers of test specimens;
- Providing physical insight into inspection data.
It is, however, necessary to validate such models and establish any limits to their validity, especially if the models are to be used to underpin the inspections of safety-critical plant.
This project is aimed at verifying the application to clad pipe of the CIVA software for modelling ultrasonic beams and its underlying theoretical formulation. However, it also has generic application to the ultrasonic testing (UT) of layered metallic components of more general geometries. The work is, for instance, relevant to the modelling of UT (either preservice or in-service) for clad pressure vessels, as used in the nuclear industry. The work will be relevant to the detection of flaws in weld zones, parent plate or the cladding, and will apply to components with external cladding as well as those with internal cladding.
This report is the first of two covering the project.
- The objective of the specific work described in this report is to verify theoretical models of ultrasonic inspection (using both focused and unfocused beams) in the unclad material using the CIVA software.