PCS-2000/DCVG

DC voltage gradient surveys are used along buried pipelines to: 

• Accurately locate coating defects 
• Estimate defect sizes 
• Identify priorities for excavation and repair 
• Provide data for cathodic protection adjustment/upgrading 
• Enable future coating deterioration to be monitored 
• Can be used to estimate levels of cathodic protection at defects when used in conjunction with potential surveys 
• Confirms electrical continuity along the pipeline and can often identify shorts to other structures 

A summary of the technique and how it is applied is contained in the PCS-2000 page. 

The DCVG is the most accurate technique available in the world for location of defects along buried pipelines.  Pin holes can be identified and the epicentre established to within a few millimetres.  SCCS surveyed pipelines buried in a built up area and located defects beneath the roads. 

The incorporation of our GPS technology has resulted in both speeding up the inspection and improving on our repeatability and accuracy of relocating pipeline coating defects. 

The technique is a DC method and normally existing cathodic protection systems are used to inject a signal by the insertion of a 1 Hz cycle current interrupter.  It is normally best to isolate away any other bonded pipelines from the pipe under test. If more than one pipe requires testing and they are all bonded together being buried in the close vicinity of one another, then they can all be tested simultaneously as defects can normally be detected several metres distant. 

If the pipeline is protected by sacrificial anodes then it is normal to use, say, a 12V battery which is put in circuit to add a boost to the signal and this increased output is interrupted for the survey. 

If the pipeline is not cathodically protected then temporary ground beds have to be established in order to inject a signal.  The pipeline under test should wherever possible be isolated from foreign structures to minimise signal loss.  Higher signals should be used when testing in built up areas or in dry/desert conditions in order to provide reasonable signals to be detected through the higher resistance ground contact points. 

The DCVG method is often compared to Close Interval Potential Surveys (CIPS).  It is important to clearly understand the differences between the two techniques. 

The DCVG technique is specifically designed for location of coating defects and to act as a delineation technique for coating refurbishment in order to balance the coating quality with cathodic protection. It is a particularly useful corrosion management tool.  Its capabilities include:

• Can be used in all situations e.g. built up areas, across mountains, across deserts, etc. 
• Unaffected by induced AC signals. 
• Unaffected by stray DC traction currents. 
• Can be used to plan future maintenance work without additional surveying. 
• Only minimal data is collected relevant to actual defects identified. 
• Can be undertaken by one surveyor. 
• The technique is extremely rapid and relatively low cost. 
• Has been successful in detecting disbonded coating. 

The PCS-2000 equipment has been developed by SCCS using the DCVG technique based on extensive experience over 16 years.  Specific advantages are: 

• Equipment has been developed with special high contact low resistance probe tips to enable accurate testing over high resistivity surfaces such as asphalt, concrete and desert. 
• Only in rare situations do holes have to be drilled through highly rubberised asphalt in order to enhance the contact.  This is unlike other equipment available on the market which needs extensive hole drilling in built up areas. 
• The instrumentation has been designed to be user friendly with auto-zeroing and clear metering for operator convenience which enhances final results. 
• Variable input impedances permit rapid and accurate readings to be obtained under all conditions. 
• The equipment is relatively light and tough being constructed largely from aluminium and fibreglass thus making it highly suitable for surveying. 
• The equipment and technique is fully supported by specialist engineers and technicians with rapid turnaround should any parts, service or support be required. 

A full set of PCS-2000 equipment comprises of the following: 

• PCS-2000 receiver 
• One pair of probes and cables 
• PCS-2000 current interrupter 
• Battery charger 
• Backpack and contact enhancing system 
• Spare probe tip 
• 50 defect location markers and holster 
• Receiver harness 
• Operator training video 
• Operator manual 
• Carry case and probe tube 

A single survey can normally test 5-10kms of pipeline per day.  Less in a built up area.   Coating quality affects the rate of progress. 

With long lengths of pipeline, we would generally send up to  two surveyors who would operate in a leapfrog manner completing typically fifteen km of survey per day along a reasonably well coated pipeline.  Older pipelines with numerous defects would obviously slow up the survey resulting in much lesser progress.  It would not be unusual to only complete around ten km per day along an older pipe.  Given a brand new pipeline with minimal defects it is possible to survey in excess of twenty km or more per day. 

It can be summarised that the progress of survey along a pipeline is affected by: 

1. The coating quality i.e. the number of defects requiring location and measurement 
2. Access along the route 
3. The quality of the cathodic protection system that exists i.e. if it can be used to inject signals or possibly temporary ground beds have to be established
4. The presence of shorts to other structures 
5. Whether the pipeline route is cross country or a built area 
6. If the route is clearly identifiable or pipe location work is also required 

It would typically take four - five hours for a reasonable proficient technician to get accustomed to use of the equipment.  The operators manual and video provided with the PCS-2000 equipment is very detailed and provides a good basis for the performance of surveys.  Obviously, all possibly situations cannot be covered in the video and the manual. 

Experience of the technician particularly in the field of cathodic protection will make a big difference as to how quickly they become proficient with the equipment.  Testing in built up areas is more difficult than other situations and therefore we recommend technicians to become familiar with setting up the equipment and testing with known defect pegs in the ground prior to commencing actual surveys. 

SCCS having  conducted more than 50,000km of pipeline surveys, provides back up support to all customers varying from fax advice to onsite training. 

As mentioned earlier, the technique only obtains data at individual defects.  Only minimal data is obtained.  When a defect is located several readings are taken around the location and at right angles to the pipeline which would complicate any computer inputs. 

However, derived data can be input continuously along the pipeline using a data logger fitted with a key pad.  SCCS undertake this form of work with global positioning systems (GPS) in order to locate defects at a later date accurately and provide a computerised output. In addition to rating defects, SCCS also allocate and plot GPS co-ordinates for test points, fences, rivers, roads, pipeline markers, TRU's, etc. 

Southern Corrosion Control Services have previously marked coating defect locations on pipelines using the following technique: 

Cross country defects are temporarily pegged and at the end of each day using the vehicle odometer for distance measurements, the pipeline is again traversed, temporary pegs removed and permanent wood pegs are installed. 

In built up areas spray paint is normally used and local reference points such as lamp posts are utilised for measurements. 

SCCS are now employing the Global Positioning System (as used by the military) to record locations of defects and fixed structures for later analysis and repair. 

For more information on our GPS solution see our GPS page. 

SCCS personnel were instrumental in 1980 in the development of the technique which was originally being used by Telstra Australia for location of deterioration on underground lead sheathed cables.  Trial sets of equipment were produced at that stage for testing of pipelines and ultimately the PCS-2000 equipment evolved.

Thus, SCCS: 

• Have accumulated 16 years of experience with the technique and to date has surveyed over 50,000 km of pipeline in all corners of the World. 
• SCCS has the largest group of professional corrosion specialists in the Asia Pacific region providing expert advise, support and field crews. 

The PCS-2000 equipment is being utilised around the World by numerous corrosion control companies, pipeline operators, plant owners and government bodies for pipeline corrosion management. 

Watch PCS-2000 video
 

Further information on this product can be obtained by e-mailing us.