Identifying Casing Shorts With or Without Test Leads - Jim Walton

1. Identifying Shorted Casings with
and without Test Leads
by
Jim Walton
Mears Group, Inc.
Integrity Solutions Division

2. Safety/OQ
• Pre-Job Meeting
• Clothing – Hard Hat, Safety Glasses, Work Boots,
Reflective Vest and other
• Equipment – Cones, Flags, Flares, First Aid Kit,
Flashers, Barricades and other
• Job Site Considerations
• Abnormal Operating Conditions
• Qualified Individuals
• Emergency Response Plan
• Job Safety Analysis

3. What methods should be utilized for identifying
shorted casings?
• Alternating Current Current Attenuation
(ACCA/CA/Electromagnetic)
• Close Interval Survey (CIS/CIPS)
• Direct Current Voltage Gradient (DCVG)
• Alternating Current Voltage Gradient (ACVG)
• Panhandle Eastern
• Casing Resistance
• Shifting the Casing potential

4. Principles of CA
• A specific signal/frequency is applied to the pipeline
• A magnetic field is created around the pipeline
• A receiving device at the ground surface receives the signal without
needing ground contact
• At areas of lower pipe to ground resistance (e.g. holidays or shorts) the
current attenuates at a higher rate
• Location, depth and distance must be established to acquire the
needed current measurement
• Distance between readings can vary (50 to 100 foot spacing is
common although distances much greater can be utilized in some
circumstances)

5. Current Attenuation Tools
PCM PPL with HDV

6. Principals of CIS
• A DC structure-to-electrolyte potential is collected during both the
CP “on” state and the CP instant “off” state
• Spacing is determined by depth of pipeline and 3 – 5 – 10 foot
spacing is common
• All influencing current should be interrupted
• All interrupters must be synchronized
• Sufficient ground contact must be achieved

7. CIS tools

8. Principles of DCVG
DCVG measures the voltage difference between two reference
electrodes. These differences can assist in pinpointing
holidays and corrosion cells on a pipeline. DCVG, because it
uses DC current, can also determine if the holiday is cathodic
(protected) or anodic (corroding) at the time the survey is being
performed.
• Asynchronous interruption (0.3sec on, 0.7sec off) is required
• Accurately locates indications of coating anomalies or shorts
• Predict relative importance/severity of anomaly.
• Must have sufficient current flow and voltage shift to obtain
accurate measurements.

9. DCVG tools

10. Principles of ACVG
ACVG uses the differences in the electrical field between two known
locations. One type of ACVG (the A-Frame) uses fixed pins on a frame
that are approximately 2’ apart. Since the distance never changes, each
data point is comparable.
Most ACVG devices will have a meter or a display that will show the
operator which way the holiday or indication is located. The severity of
the holiday is indicated by the strength of the signal at the holiday
location.
The signal strength increases until the probes are straddling and equal
distance from the holiday. Once the probes pass the holiday, the
direction changes and the strength of the signal decreases.
• Low frequency transmitter or special interrupt signal is required
• Accurately locates coating anomalies
• Predict relative importance/severity of anomaly

11. ACVG tools

12. ACVG tools

13. Sample Conditions of Cased Crossings
• Clear – No electrolyte in casing and complete electrical isolation
• No Anomalies – May have electrolyte in casing but no coating
holidays
• Electrolytic Condition – Electrolyte is present around a coating
holiday
• Metallic Short – There is metal to metal contact between the
casing and pipeline.

14. Shorted Casing Tests – Tool Methodology
• Current Attenuation (CA) – Take measurements before
and after the cased crossing.
• Alternating Current Voltage Gradient or Direct Current
Voltage Gradient (ACVG/DCVG) – Take measurements at
each end of the casing and over the cased crossing.
• CIS – Take on and off pipe to soil potentials and on and
off casing to soil potentials at the ends of the casing.
• Pipe to Casing Tests – Connect CA tool to pipeline and
casing and measure values outside the cased crossing.

15. Indirect Inspection Methods and types of Casing problems found
Indirect Method Type of Method Metallic Short Electrolytic Contact
P/S & C/S
Potentials
Electrical Potential  Low probability
P/S & C/S Shift Electrical Potential  
Pipe Current
Mapper
AC Current
Attenuation
 
PCM A-Frame AC Voltage Gradient  
Internal Resistance Electrical Resistance  Low probability
Panhandle Eastern Reverse Current
Applied to Casing
 Low probability
Pipe/Cable Locator Radio Signal  Low probability
Tinker & Rasor
Model CE-IT
Casing/Pipe
Capacitance
 Low probability
Guided Wave  
Provided Corrosion is Present

16. Portable Current Source

17. Tool Results
Results meant for Bare Casings
Coated Casings will require different criterion.
• Clear – Indirect Inspections will show no indications
across the casing.
• No Anomalies – ACVG/DCVG will show no indications;
CA over the length of the casing will show no indications;
CA utilized with pipe to casing connections may show
some loss of current outside the casing; Pipe to Soil and
Casing to Soil will be significantly different from each
other.

18. Tools Results (cont.)
• Electrolytic – ACVG/DCVG will find indications at the end(s) of the
casing and possibly over the casing (values normally <80dB). CA
over the length of the casing may show some loss (between 5 –
25%); CA utilized with pipe to casing connections should show some
loss of current outside the casing (between 20 – 80%); Pipe to Soil
and Casing to Soil will be different from each other but may be within
10 – 100 mV.
• Metallic - ACVG/DCVG will find indications at the end(s) of the casing
and possibly over the casing at the point of contact (values are
normally very high >80dB). CA over the length of the casing should
show significant loss (> 25% but may be less); CA utilized with pipe
to casing connections should show almost complete loss of current
outside the casing (> 80%); Pipe to Soil and Casing to Soil will
normally be identical (at least within 10 mV).

19. • Per DOT Part 192.921, DA can be used to assess the integrity of gas
transmission pipelines for the external, internal, and SCC threats.
• Per DOT Part 192.921, DA must be performed in accordance with
192.923, 192.925, 192.927, and 192.929, and specifically ECDA in
accordance with NACE RP0502.
From the NTSB Advisory Bulletin dated 01/03/2011
• Specifically, §192.921(a) requires the operator to select the method or
methods best suited to address the identified threats to the covered
segment (pipeline), which include internal inspection tool[s], pressure
test, direct assessment, or other technology that an operator
demonstrates can provide an equivalent understanding of the condition
of the pipeline.
• More than one assessment method may be required to address all
the threats to the covered pipeline segment.
DOT Code Requirements

20. The process assesses if a corrosion cell could exist
– Anode, Cathode, Metallic Path, Electrolytic Path
• If the coating is free of holidays, an external corrosion cell
cannot occur (absent disbonded coating issues).
• If a holiday is present, the highest risk of external corrosion
occurs with a metallic contact and electrolyte in the casing.
• If an electrolytic contact is present, a potentially corrosive
environment exists, however Cathodic Protection may be able
to polarize the pipeline.
Technical Basis

21. • Testing and field results have validated that the shorted casing
tests are applicable to cased pipelines with or without test
leads.
– Indirect Tests Find Metallic and Electrolytic Conditions
– Process Elements and Guided Wave Assess for Atmospheric Corrosion
• The process improves the safety of cased pipelines by
– identifying when potentially corrosive situations exist.
– mitigating the conditions.
– examining the integrity of the pipeline.
• Multiple applicable tools are key to having a good survey test
results across cased crossings.
• Coating condition & cathodic protection state are key in
making informed decisions about external corrosion.
• Of course any and all historical data is crucial to success.
Technical Basis

22. Questions
2 2
Jim Walton
Mears Group, Inc.
Integrity Solutions Division
1840 Hutton Drive, Suite 190
Carrollton, TX 75006
www.mearcorrosion.com
Office: 972-755-2633
Fax: 972-755-2637
Cell: 817-907-4444
email: jim.walton@mears.net