Guided Wave Inspection of Buried Pipe and the Advantages of Using a Monitoring System by Scott Lebsack

7. Considerations for Buried Pipe Inspection Soil – type, moisture Coatings – type and age Pipe age – possible degradation, coating condition Known conditions - repairs, other conditions Geometry – geometry limit GW shot lengths/sensitivity Pavement – considerations for excavations, interruption of operations Buried pipe tunnels – access conditions, penetration designs Wall penetrations – open or encased Access restrictions at wall penetrations Plant Specific Conditions

8. Underground Pipeline Coatings FBE Coal Tar and Asphalt Enamel Somastic Liquid Coating Systems (Epoxies) Wax Tapes Multilayer (3 Layer) Tapes (Cold and Hot Applied) Shrink Sleeves Polyurethanes Concrete (Weight Coatings) Coating Types Evaluated Bare pipe Coal-tar Epoxy Asphalt Enamel (Bitumen) Tapes (Cold and Hot Applied) Polyurethane There are many types of coatings and coating application processes as shown on the left. In some cases coatings are combined such as when bitumen is used as an adhesive for wraps. Most coating observed in the field is reported as general types shown on the right because owners usually do not know the specific coating or application process of older pipe. The coatings and processes is easier to identify on recently installed pipe. When uncovered in the field, coating types are usually identified as one of the general categories shown.There are many types of coatings and coating application processes as shown on the left. In some cases coatings are combined such as when bitumen is used as an adhesive for wraps. Most coating observed in the field is reported as general types shown on the right because owners usually do not know the specific coating or application process of older pipe. The coatings and processes is easier to identify on recently installed pipe. When uncovered in the field, coating types are usually identified as one of the general categories shown.

9. The GW Baseline (Optimum Conditions) Uncoated pipe on supports or hangars Distance 200 ft. + This shot is typical of one that GW sales people like to present to a prospective end user. It represents the ideal condition for the use of GW. This representation may be responsible for a lot of mis-information and therefore unrealized expectations of end-users of the technology. The shot shows the inspection of aboveground, straight runs of uncoated pipe that is on hangers. Distances in excess of 600 feet have been recorded but of course this is not what we are dealing with.This shot is typical of one that GW sales people like to present to a prospective end user. It represents the ideal condition for the use of GW. This representation may be responsible for a lot of mis-information and therefore unrealized expectations of end-users of the technology. The shot shows the inspection of aboveground, straight runs of uncoated pipe that is on hangers. Distances in excess of 600 feet have been recorded but of course this is not what we are dealing with.

10. Uncoated Pipe to Buried Uncoated Distance in soil is dependent on moisture content and soil type. Coating type will also influence distance for buried pipe. Dry sandy soil ~ 60- 90 ft. Moist sandy silt ~ 40-50 ft. Moist silt-clay < 40 ft. For buried pipe, soil type and moisture are factors as significant as coating type and age in effecting attenuation rates. The shot illustrated clearly shows the change in attenuation on the DAC curve where an uncoated pipe goes into the soil. Uncoated pipe will be most affected by fine grain soils such as clay and silt. Engineered fills, such as sand, attenuate sound less. The example shows that the distance in the buried section is approximately 40 feet, i.e., 67 to 107. Moisture also plays a role. As a rule of thumb, the lower the moisture content the better the data. For buried pipe, soil type and moisture are factors as significant as coating type and age in effecting attenuation rates. The shot illustrated clearly shows the change in attenuation on the DAC curve where an uncoated pipe goes into the soil. Uncoated pipe will be most affected by fine grain soils such as clay and silt. Engineered fills, such as sand, attenuate sound less. The example shows that the distance in the buried section is approximately 40 feet, i.e., 67 to 107. Moisture also plays a role. As a rule of thumb, the lower the moisture content the better the data.

11. Above Ground, Coal-tar Epoxy Expected distance ~ 50 ft. for older applications, can range to 125 ft. Coal-tar epoxy coatings do not restrict GW distance as much as other softer coating types unless they are freshly applied. Coal-tar epoxy coatings become brittle with age and therefore do not influence sound transmission as much as the soil surrounding it. The shot illustrated has achieved just over 100 feet. The line was in service 15 years. This shot is presented so that the effect that soil combined with this coating can be compared.Coal-tar epoxy coatings do not restrict GW distance as much as other softer coating types unless they are freshly applied. Coal-tar epoxy coatings become brittle with age and therefore do not influence sound transmission as much as the soil surrounding it. The shot illustrated has achieved just over 100 feet. The line was in service 15 years. This shot is presented so that the effect that soil combined with this coating can be compared.

12. Uncoated to Fresh Bitumen Tape-wrap Expected distance < 20 ft. for fresh applications Older applications - distances up to 45 ft. depending on age The use of bitumen as a primary coating or in combination with a wrap are highly attenuative. Note in the shot illustrated the rapid drop in the DAC curve once the interface between bare and coated pipe is crossed. The shot illustrated was a fresh application. Increasing age of the coating will reduce sound attenuation but distances over 40 feet were rare in the shots examined.The use of bitumen as a primary coating or in combination with a wrap are highly attenuative. Note in the shot illustrated the rapid drop in the DAC curve once the interface between bare and coated pipe is crossed. The shot illustrated was a fresh application. Increasing age of the coating will reduce sound attenuation but distances over 40 feet were rare in the shots examined.

13. Bitumen Tape-wrap to Buried Section   The previous slide showed the effect on sound transmission from an uncoated to coated section where the coating was a bitumen based tape wrap. The shot illustrated is the same type of coating going into a buried pipe section. The variables introduced here are soil type and the age of the coating. By comparison the attenuation drop is more significant in the previous slide due to the fact that the coating application is fresh even though this line is buried. The changes in attenuation at the points where the coating has been removed and where the pipe becomes buried are apparent even though they are in the near field.The previous slide showed the effect on sound transmission from an uncoated to coated section where the coating was a bitumen based tape wrap. The shot illustrated is the same type of coating going into a buried pipe section. The variables introduced here are soil type and the age of the coating. By comparison the attenuation drop is more significant in the previous slide due to the fact that the coating application is fresh even though this line is buried. The changes in attenuation at the points where the coating has been removed and where the pipe becomes buried are apparent even though they are in the near field.

14. Polyethylene (buried)   This example of polyethylene coating in a buried section shows a benefit to the inspection of the buried section. The influence of soil on attenuation appears to be reduced by the coating however, the soil type was not noted in this inspection. Examples of GW inspections of pipe coated with polyethylene were limited but most showed ranges from 50 to 80 feet in buried sections.This example of polyethylene coating in a buried section shows a benefit to the inspection of the buried section. The influence of soil on attenuation appears to be reduced by the coating however, the soil type was not noted in this inspection. Examples of GW inspections of pipe coated with polyethylene were limited but most showed ranges from 50 to 80 feet in buried sections.

15. Stand-off Distance   Field experience has shown that as the distance between the collar set-up position and the coating/soil interface increases the quality of the shot. Normally, this applies to a standoff distance of up to 8 to 10 feet. Beyond that no noticeable improvement is apparent. In situations where is necessary to install a the GW collar immediately adjacent to an acoustic interface, such as the penetration shown. It is worth the extra effort to take a second shot if possible at a location behind the original location. Note in the picture, that a boot is present at the penetration that needs to be removed for the initial shot. In this situation the support would influence the results of the second shot. The set-up for the shot illustrated is pictured top right. The proximity of the weld, coating and soil interface are unfortunate, however the technician has taken advantage of the extended standoff distance. Originally this pipe section was not cleaned to the extent shown. ID corrosion was found during the B-Scan of the collar set-up position as can be seen between 8 and 11 feet. Note the change in the DAC attenuation and the signal response.Field experience has shown that as the distance between the collar set-up position and the coating/soil interface increases the quality of the shot. Normally, this applies to a standoff distance of up to 8 to 10 feet. Beyond that no noticeable improvement is apparent. In situations where is necessary to install a the GW collar immediately adjacent to an acoustic interface, such as the penetration shown. It is worth the extra effort to take a second shot if possible at a location behind the original location. Note in the picture, that a boot is present at the penetration that needs to be removed for the initial shot. In this situation the support would influence the results of the second shot. The set-up for the shot illustrated is pictured top right. The proximity of the weld, coating and soil interface are unfortunate, however the technician has taken advantage of the extended standoff distance. Originally this pipe section was not cleaned to the extent shown. ID corrosion was found during the B-Scan of the collar set-up position as can be seen between 8 and 11 feet. Note the change in the DAC attenuation and the signal response.

16. Although the illustration on the slide is above ground, it has been included to show the attenuation that will occur where pipe has significant corrosion. The same will be seen in buried pipe that has extensive corrosion. If the corrosion has an extended axial length, attenuation will increase with the axial extent. In a presentation following, a case history showing a buried line with this condition will be presented.Although the illustration on the slide is above ground, it has been included to show the attenuation that will occur where pipe has significant corrosion. The same will be seen in buried pipe that has extensive corrosion. If the corrosion has an extended axial length, attenuation will increase with the axial extent. In a presentation following, a case history showing a buried line with this condition will be presented.

17. Permanently Installed Monitoring Systems (PIMS) Improved S/N ratio Improved sensitivity Eliminates excavation expense for monitoring function As an option to re-excavation to monitor pipe that contains an anomaly that does not reach repair or replacement criteria, a GW monitoring system can be installed. These systems offer the ability to monitor pipe sections without the expense of the original excavation. In addition, once the baseline data has been obtained, very small changes in the pipe section can be detected. The excerpt shows the signal responses from a clean pipe section where an anomaly has been progressively enlarged and shot. The overlaid signals show that changes less than 1% are detectable. Other benefits include the elimination of the soil to air interface signals and the ability to monitor the pipe condition from an above ground plug-in-station. The two shots shown show the differences between the original excavation and the shot taken after the PIMS collar is installed and the excavation filled. With the elimination of the signals from acoustic interfaces, sensitivity is increased and in some cases distance is also increased. As an option to re-excavation to monitor pipe that contains an anomaly that does not reach repair or replacement criteria, a GW monitoring system can be installed. These systems offer the ability to monitor pipe sections without the expense of the original excavation. In addition, once the baseline data has been obtained, very small changes in the pipe section can be detected. The excerpt shows the signal responses from a clean pipe section where an anomaly has been progressively enlarged and shot. The overlaid signals show that changes less than 1% are detectable. Other benefits include the elimination of the soil to air interface signals and the ability to monitor the pipe condition from an above ground plug-in-station. The two shots shown show the differences between the original excavation and the shot taken after the PIMS collar is installed and the excavation filled. With the elimination of the signals from acoustic interfaces, sensitivity is increased and in some cases distance is also increased.

18. PIMS Enhanced Sensitivity

19. Permanently Installed Monitoring Systems (PIMS) Improved S/N ratio Improved sensitivity Eliminates excavation expense for monitoring function As an option to re-excavation to monitor pipe that contains an anomaly that does not reach repair or replacement criteria, a GW monitoring system can be installed. These systems offer the ability to monitor pipe sections without the expense of the original excavation. In addition, once the baseline data has been obtained, very small changes in the pipe section can be detected. The excerpt shows the signal responses from a clean pipe section where an anomaly has been progressively enlarged and shot. The overlaid signals show that changes less than 1% are detectable. Other benefits include the elimination of the soil to air interface signals and the ability to monitor the pipe condition from an above ground plug-in-station. The two shots shown show the differences between the original excavation and the shot taken after the PIMS collar is installed and the excavation filled. With the elimination of the signals from acoustic interfaces, sensitivity is increased and in some cases distance is also increased. As an option to re-excavation to monitor pipe that contains an anomaly that does not reach repair or replacement criteria, a GW monitoring system can be installed. These systems offer the ability to monitor pipe sections without the expense of the original excavation. In addition, once the baseline data has been obtained, very small changes in the pipe section can be detected. The excerpt shows the signal responses from a clean pipe section where an anomaly has been progressively enlarged and shot. The overlaid signals show that changes less than 1% are detectable. Other benefits include the elimination of the soil to air interface signals and the ability to monitor the pipe condition from an above ground plug-in-station. The two shots shown show the differences between the original excavation and the shot taken after the PIMS collar is installed and the excavation filled. With the elimination of the signals from acoustic interfaces, sensitivity is increased and in some cases distance is also increased.

20. PIMS Installation Procedure Perform initial inspection of pipe Verify shot set-up & sensitivity Remove GW collar and install PIMS collar Perform test shots and compare with initial inspection Install polyurethane boot and fill with epoxy sealant Reshoot to verify installation integrity Backfill excavation, install monitoring connection and shoot baseline Expected lifetime is 20+ years

21. GW Reliability from Validated Results One of the significant findings in this study is illustrated in the chart shown. That is, 54 of 55 indications were correctly called using GW. One false positive was called. The lack of any false negatives is significant and a point that service providers have stressed based on their own experience in the field.One of the significant findings in this study is illustrated in the chart shown. That is, 54 of 55 indications were correctly called using GW. One false positive was called. The lack of any false negatives is significant and a point that service providers have stressed based on their own experience in the field.

22. Summary GW has a 10 plus year history of use for the assessment of critical piping in challenging environments. Current applications benefit from the development of GW techniques developed over the last 10 years. Defining pipe conditions for buried and in-plant piping is essential for a successful GW inspection application. Coatings and buried pipe are the two factors that most affects guided wave distance and sensitivity. Tape wraps and thick CTE attenuate sound the most. Adequate planning and consultation with an experienced GW vendor will benefit the end-user’s plant’s piping inspection program. Independent studies of GW have shown that it can reliably detect anomalies when used by qualified personnel. The qualifications of the operator remain the most significant factor using GW successfully. It is important to remember that GW has been in use much longer than its more recent use in nuclear facilities. The use evolved to include regulatory oversight and has emerged as a technique acceptable for the inspection of high pressure piping in High Consequence Areas. The current nuclear applications can benefit from a thorough review of the methodology prescribed by PHMSA and used by pipeline operators in the US. This criteria includes requirements for reporting, anomaly size criteria, shot cut off, and personnel qualifications. With respect to nuclear applications as with any application, a complete definition of the existing pipe conditions will contribute to the success of the use of GW if it is selected. This information is essential for the GW service provider analyze data that is obtained during the inspection. Coated and buried pipe represent the most challenging circumstances for applying GW yet if applied within the limitations known, useful information will be collected. It has been shown that tape-wraps and thick, fresh CTE or Bitumen attenuate sound the most and offer the greatest challenge for inspection. Additional information relating to piping that is to be inspected, such as geometry, wall penetrations, etc., is also important in determining how and where GW will produce the best results. Finally, the at this point in the application of GW to buried piping, the experience of the technician and the information he has at his disposal are the two factors most influencing the success of a project. It is important to remember that GW has been in use much longer than its more recent use in nuclear facilities. The use evolved to include regulatory oversight and has emerged as a technique acceptable for the inspection of high pressure piping in High Consequence Areas. The current nuclear applications can benefit from a thorough review of the methodology prescribed by PHMSA and used by pipeline operators in the US. This criteria includes requirements for reporting, anomaly size criteria, shot cut off, and personnel qualifications. With respect to nuclear applications as with any application, a complete definition of the existing pipe conditions will contribute to the success of the use of GW if it is selected. This information is essential for the GW service provider analyze data that is obtained during the inspection. Coated and buried pipe represent the most challenging circumstances for applying GW yet if applied within the limitations known, useful information will be collected. It has been shown that tape-wraps and thick, fresh CTE or Bitumen attenuate sound the most and offer the greatest challenge for inspection. Additional information relating to piping that is to be inspected, such as geometry, wall penetrations, etc., is also important in determining how and where GW will produce the best results. Finally, the at this point in the application of GW to buried piping, the experience of the technician and the information he has at his disposal are the two factors most influencing the success of a project.

23. References GTI PROJECT NUMBER 20386, Demonstration of ECDA Applicability and Reliability for Demanding Situations DOT Prj#195, Daniel Ersoy daniel.ersoy@gastechnology.org