• Accurately locates coating defects.
• Estimates defect sizes.
• Estimates levels of CP protection at defects.
• Identifies priorities for excavation.
• Provides data for CP adjustment/upgrading.
• Enables coating deterioration to be monitored.
• Also confirms electrical continuity and locates shorts.

Features

• High accuracy coating defect surveying.
• Rapid technique requiring 1 person.
• Incorporates the proven reliability of the DC voltage gradient technique.
• Advanced, patented electronics.
• User-friendly operation.
• Ergonomic design for surveyor comfort.

Environments

The PCS-2000 and development models have been tried and proven under harsh and varying conditions:

• Across deserts, streams and rocky terrain.
• Along asphalt and concrete paved roads.
• Near electrified DC rail systems and overhead power lines.
• During extreme weather conditions.

Benefits

• The most efficient and accurate method available to detect pipeline coating defects and damaged cables.
• Advanced electronics make it uncomplicated and easy to use.
• Proven across asphalt, concrete, deserts and rocky terrain - unaffected by stray currents, induction and static.
• Pinpoints defects, assesses sizes, levels of CP protection and maintenance requirements.
• Versatile equipment unsurpassed in speed and accuracy for underground utility owners and service companies.

The PCS-2000 is designed for use by operators, inspectors and technicians. No previous experience is necessary, as the equipment is simple to use. A training video plus manual provide comprehensive instructions. An average person can gain proficiency in under four hours.

Sophisticated electronics detect signal voltage gradients to provide rapid visual interpretations at defect locations. An easy to read meter panel and the convenience of several scales permits speedy location and assessment.

Probe polarity provides a left-right meter deflection to indicate the direction of a defect. For example, when the right probe precedes the left probe and the meter deflection is to the right, the defect is right ahead.

The ability to test over bitumen is a unique feature of PCS-2000. Specially designed probe tips, the probe contact enhancing system, high input resistance sensitivity and advanced noise rejection design combine to provide a capability unparalleled by other surveying equipment.

A single operator can survey on an average 5 miles (8 km) of pipeline per day. This varies with pipeline access and coating quality. Ease of operation, rapid surveying, high accuracy, unique features and ergonomic design makes PCS-2000 indispensable for owner-operators and service companies.

A comprehensive set of equipment is supplied as standard. It contains all the equipment and instruction necessary to undertake a survey. Service and technical backup are available from Farwest Corrosion Control Company.

Knowledge of the coating condition on a buried pipeline enables maintenance program to be formulated. Unless there is a certainty of the condition, sole acceptance of potentials at test points spaced often 1 - 2 km apart may lead to a false sense of security, as potentials between test points may not indicate protection.

DC voltage gradient surveys have evolved as the most accurate and economic means of locating coating defects. The PCS-2000 utilizes this method to detect defects.

When a DC current is applied to a pipeline in a similar manner to cathodic protection, ground voltage gradients are created due to passage of current through resistive soil. Well coated pipelines have a high resistance to earth. However, at locations where there are coating defects the resistance to earth is such that current can flow through the soil to be picked-up by the pipe. In the vicinity of these defects measurable voltage gradients can be detected at ground level. The larger the defect the greater the current flow. Increasing the current flow also results in an increased voltage gradient for a given soil resistivity.

The application of DC current to a pipeline at a regular pulsed frequency using the PCS-2000 interrupter enables coating defects to be distinguished by stray traction and telluric currents. Existing cathodic protection systems may be utilized to inject the required signal, or temporary earths may be established at convenient connection points along the line.

The surveyor traverses the line using two non-polarizing electrodes in conjunction with the PCS-2000 receiver. As the surveyor approaches a coating defect, a pulsing signal is detected by the receiver.

The electrodes are placed at 2 or 3 differing locations to confirm the validity of the indication and exact defect location. Probes placed across voltage gradient lines will indicate a voltage deflection. This signal is indicated by the meter. Probes placed along equi-potential lines will result in the meter pulling. Tracing of the voltage gradients will rapidly locate the defect epicenter.

Having detected the epicenter, a series of lateral readings are taken, moving away to remote earth. These readings combined with the signal strength enable the coating size and reduction in CP protection levels to be estimated. Historical knowledge of the line and experience from excavation work enables a more detailed and accurate analysis to be performed.

PCS-2000 Background

What happens at a coating defect?

Cathodic protection provides backup protection for areas of the pipe where the coating has been damaged. Current flows to the exposed pipe surface and shifts the potential in a negative direction. Well protected areas will generally build up a calcareous film deposit. A ring deposit will often be observed at defects. The deposit layer is always thickest at the defect edge. This is because cathodic protection current can flow more easily to the edges rather than the center.

  
A bathtub-type curve of potentials can be measured across the defect face. Most negative potentials existing at the edges. On a given pipeline, larger defects have greater potential dips in the middle. Thus, on any coated pipeline the cathodic protection system has a limitation on the size of defects which can be protected.

Can't we increase rectifier outputs to fully protect defects?

In summary, no. The fact is that once we polarize the pipe surface to around -1.17 V versus Cu/CuS04, a region of overprotection is entered. Increasing the CP current once an "off" potential of around -1.22 V is achieved simply increases the hydrogen evolution at the cathodic surface. This frequently results in coating disbandment. Also associated with overprotection is alkali generation. Alkali can act as a very effective paint stripper on some coatings. Ideally, "off" potentials should be maintained in the range of -0.85 to -1.15 V versus Cu/CuS04.

What does this mean for a pipeline that has small and large sized coating defects with potential surveys indicating full protection?

While trying to prevent coating disbandment, the probability will be that the small defects are fully protected and large ones are possibly underprotected. If there is unbonded coating then shielded corrosion could be occurring adjacent to both small and large defects. Several small defects close to each other runs a greater risk of experiencing underprotection than if they were widely distributed. It is therefore economic to:

• Delineate large defects from small ones.
• Repair the largest defects and allow the cathodic protection system to protect the smaller ones.

It would only be necessary to excavate some or all of the smaller defects if the coating is found to be disbanding and shielding corrosion is occurring. Sole reliance upon potential measurements for assessing corrosion protection is both uneconomical and risky.

The philosophy of the technique is to use more than one monitoring method to determine the effectiveness of the protection system. One can have a degree of confidence that no corrosion is occurring if all the results indicate that full protection is being afforded.

Objectives:

• Optimize the effectiveness of the installed cathodic protection system.
• Avoid overprotection which can lead to coating disbandment.
• Reduce coating defect sizes to a level where the cathodic protection system can provide full protection.
• Provide a basis for ongoing monitoring of the cathodic protection system and coating.

What the results tell you:

• Accurately locates coating detects. The PCS-2000 method is the most accurate and sensitive survey method developed to locate coating defects. It has also been refined to test pipelines in built-up areas using a patented technique.

• Defect sizes. Experience has shown that where a pipe is buried at a 3 - 5 ft (1 - 1.5 m) depth, a 5% IR represents approximately a 2 in² (12 cm²) defect. Pipe depth varies the signal strength measured at the surface. Coupons connected to the pipe with known bare areas enables the defects to be calibrated.

• Continued coating deterioration. Percentages IR calculated from surface readings are permanent defect benchmark figures which will be noted on subsequent surveys to increase if the coating deteriorates further.

• Reduction in protection. The overline to remote earth potential drops can be used directly to determine potential drops at defects.

• Priority for refurbishment. Defects with the largest percentages IR are given first priority for recoating. The cathodic protection system should be able to protect the smaller defects. Small defects should be investigated where the pipe is experiencing coating disbandment. Plotting of the defects enables easy assessment of the coating condition and acts as a good management reporting format.

• Cathodic protection system adjustment or upgrade. The survey together with test point potentials identifies sections with under or over protection. The latter is frequently found at impressed current system drain points where current outputs have been regularly increased due to reducing protection levels. This is a self defeating practice, as it leads to further coating damage. It may be necessary to provide supplementary protection between rectifier stations in order to even out the spread of protection.

1. Meter dial layout is designed for easy reading with an accuracy Class 1 ASC42. It has a pivoted spring suspension action and a high sensitivity 100 / 1000 megohm input resistance.
2. On-Off switch incorporates a battery test.
3. A 1.2 AH rechargeable battery enables up to 50 hours of operation before requiring a recharge.
4. Range selection available provides the operator with a high degree of flexibility when surveying differing coating qualities.
5. Input impedance selection for testing across normal terrain or high resistance surfaces.
6. Black powder coated aluminum case.
7. Auto-zero button automatically returns meter needle to zero position for ease of taking readings.
8. Soft foam comfortable hand grip.
9. Sturdy cables with positive lock connectors.
10. Lightweight aluminum construction.
11. Easy-to-maintain non-polarizing copper/copper sulfate reference electrodes.
12. Built-in probe contact enhancing system for asphalt, concrete and dry soils.
13. Current interrupter for signal injection. Switching capacity 30A at 12V, 5A at 50V DC only with a rechargeable 1.2 AH battery giving up to 12 hours of operation before requiring a recharge. LED indicates low battery.