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 Remote Visual Inspection |
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| Specialist NDT |
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| Flexible Pipe Integrity |
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 CP Survey |
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Corrosion prevention of underwater structures and pipelines by cathodic protection technology is an established technique, which requires regular monitoring to ensure effectiveness. iicorr are market leaders in the field of specialist inspection and monitoring with a proven track record. Cathodic protection survey is a core area of expertise with an extensive client base covering a worldwide market. iicorr provide a fully integrated Cathodic Protection inspection service ranging from land based to ROV mounted survey of subsea installations and pipelines. iicorr have developed a survey team of a very high technical calibre. The team provides the expertise to acquire, analyse and report data as required by our clients, while conforming to the highest safety standards. iicorr Cathodic Protection Services are able to provide this high quality, cost effective service through a combination of proven technology and world leading engineering capability. We are able to realise a rapid response to our clients needs on a worldwide basis as a result of iicorr's international business streams. |
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| Why use iicorr? | |||||
iicorr have operated in over 20 countries worldwide, supported by our bases in Aberdeen, Houston, Kuala Lumpur and Perth, Australia since commencing offshore Cathodic Protection Surveys in 1977. The survey techniques and equipment that have been developed by the company during this time, are continually updated and improved by a dedicated team of engineers with a view to providing a reliable and accurate survey service. |
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| CTC-2 Technique | |||||
Based on the Cell to Cell (CTC) technique for CP measurements, the CTC-2 system, combines cathodic protection profile and electric field gradient of submarine pipelines in conjunction with ROV surveys. The system comprises the CTC-2 contact probe for obtaining "absolute" potentials of exposed sections of bare metal or anodes on submarine pipelines. The CP profile of the pipeline is measured with reference to a marinised Ag/AgCl cell in conjunction with the offset value from the calibration contact measurement and a remote half cell usually deployed from the survey vessel - commonly referred to as the "towed remote" a trailing wire connection can be used in place of the towed remote. The electric Field Gradient is measured simultaneously with the potential by means of the integral matched pair of Ag/AgCl reference cells which can be used to detect "active " coating damage and allow current output and remaining life of the pipeline's sacrificial anodes to be calculated. The data is correlated with the corresponding position fix (KP), provided by the survey computer. It is possible to display the raw CP & FG values on video overlay if required. |
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CTC-2 Technique |
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| Trailing Wire Technique | |||||
The trailing wire technique is used when the pipeline is buried, close to the shoreline or where it is not possible to obtain direct contact with the pipe at the point of measurement. Since the resistance of the pipe and the wire is small with respect to the measuring device, the potential of the pipe can still be measured locally even if the contact point is several kilometres way from the point being measured. |
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Trailing Wire Technique |
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| Operation | |||||
Readings are to be obtained from the test post on land using a Copper/Copper Sulphate (Cu/CuSO 4 ) electrode. This takes the form of a copper electrode immersed in a saturated CuSO 4 solution. The components are contained in a Perspex tube with the electrical contact at one end and a porous plug at the other. This plug allows the solution to make contact with the ground, completing the electrical circuit via a voltmeter to the test post. Readings obtained are 60mV more negative than those of a Silver/Silver Chloride [Ag/AgCl] electrode and therefore are used as a check to ensure continuity with the pipeline was achieved before the trailing wire survey commenced. A 15km drum of trailing wire will be connected to the data acquisition system and then fed from the stern of the vessel and connected to the test post. A Silver/Silver Chloride reference electrode, also connected to the data acquisition system, is then also deployed from the stern of the vessel. It is recommended that the Silver/Silver Chloride Electrode be attached to the towed fish, so that the fish can keep the Electrode in close proximity to the pipeline for the duration of the survey. However, in shallow water areas this is not always possible. Once a good connection to the pipeline has been established, logging of the data can commence. The vessel then proceeds along the pipeline survey route away from the start point. As the survey vessel proceeds along the route, the depth of the reference cell is adjusted to maintain a position as close to the pipeline as is practical. The trailing wire payout is maintained until the required distance of the pipeline has been surveyed. The position of the vessel is relayed to the survey computer as Kilometre Post (KP) and the CP values are recorded against KP position. |
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| Equipment | |||||
| Subsea Digitizer | |||||
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iicorr offer a versatile, compact and robust CP subsea digitizer for fast and reliable transmission of CP data via ROV umbilicals. The CP digitizer is small, lightweight and user friendly. It is designed for ROV mounting and provides easy-interface data transmission. Based on tried and tested PLC and RS458 or RS232 transmission, it features a single calibration per ROV interface. |
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| Selecting RS485 or RS232 data transmission | |||||
| RS232 will normally be used if the data is being sent via a data-mulitplexer. RS485 will normally be used if the data can be sent via a twisted pair in the ROV umbilical. Data is made available as RS485 and RS232 simultaneously, and selecting the required transmission type is simply a matter of connecting the correct pin-outs. | |||||
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Example of RS485 configuration |
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| CTC-2 Probe | |||||
The CTC-2 probe is unique to iicorr and comprises of one matched pair of Ag/AgCl half cells and an inconel stab tip for obtaining cathodic potential with field gradient measurements. The probe must be held axially to the pipeline to obtain accurate field gradient measurements. Direct CP measurements are obtained for calibration by stabbing an anode or exposed pipe at regular intervals along the pipeline, while local variations in CP and FG are detected with reference to a remote half cell towed beneath the vessel.
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| CP Contact Probe | |||||
The CP contact probe incorporates one high purity Ag/AgCl half cell for measuring cathodic potentials on a marine structure or pipeline. The contact probe is used to obtain direct values of cathodic potential on exposed steel or anodes. The hand held or ROV mounted probe is extremely robust and reliable, and can be used in conjunction with a remote reference electrode to also measure proximity CP potentials.
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