External Corrosion Direct Assessment (ECDA) - inaccuracies and limitations of this NACE recommended practice

摘要

The ECDA concept embodied in NACE RP 2002.050 is increasingly being used internationally as a way of gathering above ground data to establish the Integrity of Pipelines that cannot usually be inspected by inline tools (ILI). The RP identifies ECDA as a four stage process: Pre Assessment. Collecting and analysing historic and current data. Define ECDA regions and selects Indirect Inspection Tools; Indirect Inspection. Above ground inspections with two or more techniques to gather data for analysis; Direct Examination. Analyse data to determine excavation locations. Carry out digs to inspect pipeline and record any metal loss etc; Post Assessment. Covers analysis of data gathered from the three previous steps and assess the effectiveness of the ECDA process. Often in use, little thought is given to in built inaccuracies, misleading sections and omissions of the NACE RP which in some aspects reflect vested interests rather than science of the subject. This paper identifies only some of these limitations. At the same time some limitations of inline inspection tools are presented which are often oversold in terms of their accuracy and their limited contribution to improving ongoing corrosion control. A clear ECDA direction is set out as to the correct survey information to collect for analysis in order to achieve the most cost effective repair of corrosion mitigation techniques for long term improvement in pipeline integrity. The RP originally made available in 2002 should have undergone drastic redrafting beginning in 2006 but that seems to have been shelved for political reasons. Document NACE RP2002.050 has now been re-issued with negligible changes as NACE SP0502- 2008. From its inception it has been called a Standard Recommended Practice and is now called a Standard Practice. It is in fact a Recommended Practice because NACE is not a Standards Issuing Body such as ASME or ISO or BSI. Unfortunately the misrepresentation seems to have duped some of these bodies into incorporating reference to SP0502-2008 without thought to the inbuilt inaccuracies etc. of the document. During this paper references are made to various sections of SP0502-2008. Access to a copy is useful to fully understand the comments and criticisms made.