CIP survey

CIP surveys are used to identify the levels of protection that exist along pipelines. Today, it is well accepted by the industry that point measurements only at test posts are insufficient to judge the overall condition of the pipeline. To solve this problem and get a clear overview of the total length of the pipeline, a trailing wire is pulled from the nearest test point and potentials are taken at typically 1.5-metre interval along the entire length of the pipeline. This approach has now become best practice in the industry.

Principle of survey

The close interval potential survey provides a detailed profile of the potential level along the entire route of a pipeline. This profile can be used to assess the performance of the cathodic protection system and also provides information on the coating system and interaction effects.

Potentials are normally recorded at intervals between 1 and 5 metres to provide a continuous pipe to soil potential profile. If recorded with the CP system 'ON', the measurement will include an 'IR volt drop' component in the reading caused by the flow of CP current in the soil. To overcome this error, timers are fitted in the DS circuit of the transformer rectifiers or other power supplies to interrupt the protection current. Where protection is provided by two or more sources, the timers must be synchronised to interrupt all current sources simultaneously. Potentials recorded immediately after interruption (before significant depolarisation has occurred) will then be free of the IR component and are referred to as polarised or 'instantaneous OFF' potentials.

In areas where stray currents cause pipe to soil potentials to fluctuate, stationary data collectors are also employed at selected test locations during the survey.

Site equipment

Microprocessor controlled data collector/voltmeter with a minimum input impedance of 10Mohms and an adequate level of AC rejection.

Copper/copper sulphate reference electrode(s) fitted to pole(s).

Synchronised timers/current interrupters for switching DC power sources.

Insulated wire, which may be disposable or re-usable, wound on dispenser and distance recorder.

Pipeline location equipment.

Survey procedure

If polarised potentials are required, synchronised timers/current interrupters are installed in all transformer rectifiers or other DC power supplies providing CP current to the pipeline.

Where the route to be surveyed is subject to interaction or fluctuating potentials, stationary recording units are installed.

Unless the exact route of the pipeline is known or marked out ahead of the survey, a survey assistant is used to locate the pipeline route immediately ahead of the survey operator.

The insulated wire is connected to the pipeline (usually at a CP test post), the survey proceeds with the operator carrying the mobile data collector/voltmeter and placing a copper/copper reference electrode on the ground above the pipeline at the required intervals. Features along the route are entered into the data collector manually to assist in interpretation. Survey sections between connection points should be minimised wherever possible and on completion of each section the wire trailed out should be collected for disposal or re-use.

Data obtained

The CIP survey provides a continuous plot of both 'ON' and 'instantaneous OFF' pipe to soil potentials and these plots may be interpreted to indicate area of poor levels of protection due to poor coating, interaction from other sources, soil conditions and failure of the cathodic protection system. A hard copy of this data obtained which is useful for record purposes and for comparison with the past and future data.

Processing and presentation of data

Raw data is transferred to computer/floppy disc on completion of each day's survey and the data checked to verify accuracy and that equipment was fully functional and to identify any areas which may require immediate re-survey.

Data collected from a CIP survey is normally processed by computer and presented in graphical form.

Manpower and Vehicles

A close interval potential survey team would normally be undertaken by a minimum team of two men. One operator would locate the pipeline and the second perform the actual survey. In practice, a third team member is useful to assist the operator, retrieve the wire and process the raw data. To work efficiently, two vehicles are required.

Advantages of the CIP survey

• Provides a complete pipe to soil potential profile on the pipeline for both 'ON' and 'polarised OFF' potentials.

• The entire pipeline section is walked enabling an inspection of CP equipment and the right of way at the same time as the survey.

• A hard copy of the survey data is produced allowing easy identification of defect areas by non-technical personnel.

• A base line survey of the pipeline potentials can be obtained providing guidance for future operation and maintenance of the CP system.

• Provides information on CP levels at coating defects and likely active corrosion location.

• Identifies areas of stray current interaction.

• Survey less reliant on survey team for interpretation of result.

• Progress is independent of coating quality.

• Can easily be combined with integrated GPS and/or DCVG measurements

Our experienced inspectors are well trained to analyse the gathered data and prepare a detailed report, which includes recommendation for corrective actions, or need for further detailed investigation.
They work fully compliant to our extensive Standard Operating Procedures and our safety manuals.

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