Non-intrusive assessment of pipeline Coating and Cathodic Protection (CP) is performed by utilising aboveground surveys, also known as Indirect Inspection. However, there have been two major advancements with these Indirect Inspection survey techniques – (1) Combining multiple aboveground surveys into a single GPS integrated dataset for automatic alignment, better correlation and accuracy, (2) Encrypted recording of raw logs to prove the authenticity of the obtained datasets. Integrated Inspection Techniques (IITs) have the ability of combining up to nine (9) different surveys – CIPS, DCVG, CAT, ACVG, DOC, AC-PSP, Soil Resistivity, Gas-Leak and GPS. All these surveys are conducted by walking only once over the pipeline and the surveys record datasets continuously at up to 35 times per second. Encrypted data is auto-integrated and recorded by the equipment, and further analysed on the viewable software for assessing the pipeline's external integrity. This paper discusses the direct and indirect results from IITs from field experiences.
Direct results include – (1) CP under/over protection, (2) Coating faults, (3) Low depth of cover zones, (4) Soil resistivity/corrosivity, (5) Gas leak locations, (6) Geo-tagged photographs.
Indirect results include – (1) Locations of active corrosion, (2) AC/DC interference areas, (3) Telluric interference areas, (4) Transformer Rectifier malfunction, (5) Authenticity of data over concrete/interlock/challenging surfaces.
Pipelines are laid in the harshest of environments. From enduring extreme heat in sandy environments to sub-zero temperatures near the Arctic Circle, pipelines have primarily two layers of defence – Coating and Cathodic Protection (CP), for managing the external integrity.
Majority of the traditional aboveground CP and Coating survey techniques being utilized in the industry are offered with several hurdles – the most important being the authenticity of the datasets being collected.
The other two approved pipeline integrity validation techniques of In-Line Inspection and Hydrotesting overcome this hurdle by recording continuous raw data and pressure cycles. However, this was missing from the aboveground indirect inspection surveys.
Integrated Inspection Techniques (IITs) solve this problem by recording encrypted waveforms which may be used after the survey for detailed analysis in office and by the pipeline owner for the purpose of future audits. The continuously recorded waveforms help in identifying bad / incorrect data which could be obtained due to multiple issues such as high depth of cover (sand dunes), transformer rectifier malfunction, challenging concrete/asphalt surfaces and many more. Thus, it helps the pipeline owner to make informed integrity decisions. The waveforms also help in locating AC and DC interference susceptible zones.
