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PRCI PR-3-703
- Field Techniques to Determine Electrical Shorts between Carriers
- Report / Survey by Pipeline Research Council International, 12/01/1988
- Publisher: PRCI
$125.00$249.00
L51587e
Battelle Memorial Institute
(e-Book Version)Need: Corrosion protection of pipelines inside casings recently has received increasing attention. Although, historically, the safety record of operating pipelines within casings has been excellent, recent experience of the pipeline industry has suggested that potential problems may exist and improved or new field techniques for monitoring the effectiveness of corrosion control practices need to be developed specifically for the pipeline within casings. Furthermore, the mechanism or the root cause of corrosion of pipelines inside casings needs to be better understood.
Benefit: The objectives of the research have been to develop a reliable field technique, based upon the AC-impedance technique, to determine whether or not a carrier pipe is electrically (metallically) shorted to a casing pipe, and to develop a prototype instrument for field use. During 1987, Task 1 "Development of a Field Technique to Determine Electrical Shorts" was performed. Major subtasks performed in Task 1 were a review of the currently available field techniques for electrical short detection, laboratory tests to develop methodology based on the AC-impedance technique, and a series of field tests to assess the feasibility of developing a field technique based upon the methodology established in the laboratory. During 1988, Task 2 "Prototype Instrument Development" was performed. A first-edition prototype was constructed, laboratory tested, and field tested.
Result: Based upon the findings of this research, the following conclusions are deduced. (1) Of the existing field techniques for determining the electrical status, the
Panhandle method is used by the pipeline industry as the final method when other methods leave some doubt regarding the status. During this research, the Panhandle method was compared to the new technique developed at Battelle. A reasonably good agreement was observed between the results obtained by the two respective methods. (2) The new method developed based upon the AC-impedance measurement technique, using the laboratory type instrumentation, performed well in the field. The results of the field tests on about 45 casings showed that the technique is capable of determining the status of electrical isolation of a casing. A constant resistance (impedance) value over the range of frequencies used was obtained for a shorted casing, while a gradual increase in resistance (impedance) with decreasing frequency was observed for an unshorted casing. The results confirmed that the principle upon which the technique is developed is quite applicable to casing short detection in the field. (3) The results of the limited field test with the first-edition prototype on seven casings showed that the prototype is capable of determining casings that are shorted. Although the instrument was capable of determining the unshorted status, the sensitivity of the prototype in detecting the gradual rise in impedance with decreasing frequency needs to be magnified. It appears that strong AC currents, if present on a pipeline, reduce the sensitivity of the instrument. Graphic presentation of the data needs to be improved to permit a more accurate interpretation. (4) Additional work is necessary to improve the operation of the prototype unit to overcome the problems stated in Conclusion (3) above. (5) The use of the Battelle methodology with the yet to be developed field instrument, would be simpler to use and less time consuming than any other of the presently existing methods.
Battelle Memorial Institute
(e-Book Version)Need: Corrosion protection of pipelines inside casings recently has received increasing attention. Although, historically, the safety record of operating pipelines within casings has been excellent, recent experience of the pipeline industry has suggested that potential problems may exist and improved or new field techniques for monitoring the effectiveness of corrosion control practices need to be developed specifically for the pipeline within casings. Furthermore, the mechanism or the root cause of corrosion of pipelines inside casings needs to be better understood.
Benefit: The objectives of the research have been to develop a reliable field technique, based upon the AC-impedance technique, to determine whether or not a carrier pipe is electrically (metallically) shorted to a casing pipe, and to develop a prototype instrument for field use. During 1987, Task 1 "Development of a Field Technique to Determine Electrical Shorts" was performed. Major subtasks performed in Task 1 were a review of the currently available field techniques for electrical short detection, laboratory tests to develop methodology based on the AC-impedance technique, and a series of field tests to assess the feasibility of developing a field technique based upon the methodology established in the laboratory. During 1988, Task 2 "Prototype Instrument Development" was performed. A first-edition prototype was constructed, laboratory tested, and field tested.
Result: Based upon the findings of this research, the following conclusions are deduced. (1) Of the existing field techniques for determining the electrical status, the
Panhandle method is used by the pipeline industry as the final method when other methods leave some doubt regarding the status. During this research, the Panhandle method was compared to the new technique developed at Battelle. A reasonably good agreement was observed between the results obtained by the two respective methods. (2) The new method developed based upon the AC-impedance measurement technique, using the laboratory type instrumentation, performed well in the field. The results of the field tests on about 45 casings showed that the technique is capable of determining the status of electrical isolation of a casing. A constant resistance (impedance) value over the range of frequencies used was obtained for a shorted casing, while a gradual increase in resistance (impedance) with decreasing frequency was observed for an unshorted casing. The results confirmed that the principle upon which the technique is developed is quite applicable to casing short detection in the field. (3) The results of the limited field test with the first-edition prototype on seven casings showed that the prototype is capable of determining casings that are shorted. Although the instrument was capable of determining the unshorted status, the sensitivity of the prototype in detecting the gradual rise in impedance with decreasing frequency needs to be magnified. It appears that strong AC currents, if present on a pipeline, reduce the sensitivity of the instrument. Graphic presentation of the data needs to be improved to permit a more accurate interpretation. (4) Additional work is necessary to improve the operation of the prototype unit to overcome the problems stated in Conclusion (3) above. (5) The use of the Battelle methodology with the yet to be developed field instrument, would be simpler to use and less time consuming than any other of the presently existing methods.
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