ABSTRACT In-line inspection (ILI) of pipelines has established itself as the most efficient tool for evaluating the condition of a pipeline and an indispensable part of pipeline integrity management. This paper describes the new generation of ultrasonic ILI tools, both for metal loss (corrosion) and crack detection. This paper shows how requirements on ILI data and ensuing defect assessment procedures; influence the development of new tools. The performance of these new tools is discussed, their detection and sizing performance, as well as their operational characteristics and improved reporting. It is demonstrated how the new ultrasonic (UT) metal loss tools provide superior results over others in fully using the most advanced defect assessment algorithms.
Inspection of pipelines for crack and crack-like defects is another aspect where this technology offers the highest standards within the industry. Examples are shown of how cracks and crack-like defects of different kinds can be reliably detected classified and sized using this technology. Most recent results obtained with the described technology are shown, illustrating the performance and fields of application.
INTRODUCTION As pipeline integrity management becomes an area of increasing interest worldwide, in-line inspection (ILI, also called intelligent or smart pigging) gets into the focus as one of the most efficient and straightforward ways to assess the condition of a pipeline. Several technologies of ILI are available nowadays and emerging new NDT techniques will even enhance that choice in the future.
Pipeline operators have been using several defect assessment methods to evaluate the remaining strength of their pipelines based on the input data obtained from ILI tools. Often instead of appropriate assessment calculations just a quick ranking is being done and in that case the limitations of the methods are often not considered. In the end, nevertheless, the distinction is not obvious for the pipeline operator between a calculation carried out precisely according to the code and a rough one performed to produce a quick ranking
When planning to use ILI data for defect assessment, however, it is essential to know what kind of data needs to be acquired in the first place in order to allow for carrying out certain assessment calculations. In the usage of ILI technologies, and especially development of new ones, the knowledge of pipeline integrity assessment methods and their requirements is the key input for the specification of technical requirements of such tools1.
EFFECTS OF TOOL ACCURACY ON DEFECT ASSESSMENT
All the data used for defect assessment, including data obtained from ILI tools, have an inherent measurement error. Usually, ILI vendors state the accuracy of tools in data sheets and final reports2. When using defect geometry for assessment purposes, errors of measurement are usually ignored and other safety factors are introduced in assessment codes for compensation. Only the code of Det Norske Veritas Part A3 allows for input of ILI tool accuracy and measurement technology, by introducing probabilistically calibrated coefficients. To demonstrate the effect which tool accuracy has on defect severity evaluation, we carried out sample calculations using capabilities of ILI tools available today.
Table 1 shows defect specifications of tools used for metal loss measurements, given in percent of the wall thickness for magnetic flux leakage (MFL) tools and in mm for ultrasonic testing (UT) tools, with commonly specified accuracies assumed for the calculations.