The DA module offers the following advantages when performing an ECDA:

	the DA module is an integral part of PiMSlider®, thus giving the benefit of easy access to all relevant data from the pipeline under investigation as well as from other pipelines
	the DA module offers considerable time-saving, increased transparency and better reproducibility throughout the ECDA process
	the DA module enables quantification of each mitigating activity to the overall integrity of the pipeline, thereby minimizing the overall cost of mitigating measures
	the DA module accounts for the uncertainties generally associated with ECDA

Indirect Inspection Results

ECDA Distribution

Source Data Segmentation

External Corrosion Direct Assessment

A significant part of the world's pipelines are considered unpiggable due to various configuration issues. In North America, External Corrosion Direct Assessment (ECDA) has become acknowledged by the Office of Pipeline Safety as a viable alternative to both in-line inspections and hydrostatic pressure testing, for assessing the integrity of high pressure pipelines. According to the existing standard, the main goal of ECDA is to prevent external corrosion defects from growing to a size that is large enough to impact structural integrity. "The process integrates information on a pipeline's physical characteristics and operating history (pre-assessment) with data from multiple field examinations (indirect inspections) and pipe surface evaluations (direct examinations) to provide a more comprehensive integrity evaluation with respect to external corrosion (post-assessment)" [NACE RP0502-2002].

The Direct Assessment Module

To ensure safe operation of the unpiggable pipelines in The Netherlands, a Direct Assessment (DA) module for PIMSlider has recently been developed, based on Structural Reliability Analysis (SRA) and Bayesian updating techniques. This module enables computerized storage, retrieval and processing of all appropriate pipeline data and therefore guarantees highly accurate, reproducible and time saving integrity analyses of a pipeline grid. An important function of this system is the ability to use the complete database of all pipelines to pre-assess the integrity of a particular pipeline. This automated retrieval of data from pipelines with similar characteristics and/or environmental conditions results in a substantial increase of accessible data and enables the pipeline operator to improve the reliability of applied statistics throughout the process. As a consequence, the overall cost of inspections and excavations can be greatly reduced.

Pre-Assessment

In the Pre-Assessment phase, the DA module assists the integrity manager in gathering and analyzing data necessary to determine the current condition of a pipeline. After collection and visualization of the available data, the module defines suitable ECDA regions, based on parameters and criteria chosen by the user. Furthermore, the gathered data are used to construct prior distributions of parameters relevant to the SRA model, such as the number and size of corrosion defects and pipeline-related parameters.

Indirect Inspections

In the Indirect Inspections step, the DA module allows the user to store and analyze the data from aboveground surveys, in order to determine the severity of coating faults and to identify areas where corrosion activity may occur. The probabilistic methodology accounts for the individual performance of each applied survey technique in terms of missed defects and false indications, in general a major source of uncertainty in ECDA.

Direct Examinations And Post-Assessment

In the Direct Examinations phase, excavations are carried out to verify the results from the Indirect Inspections and to characterize possible corrosion anomalies. Subsequently, the ECDA module uses this information in the Post-Assessment phase to update, among other things, the parameters concerning the performance of survey techniques, the number of defects and the corrosion rate. As a result, updated failure frequencies are calculated for each ECDA-region (after each excavation if required). These are used by the DA module to advise the integrity manager whether additional mitigating activities are necessary, or by calculating a reassessment interval for the pipeline under investigation.