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DCVG Dig Selection – Above & Beyond %IR - Ryan Swor
- 1. DCVG Dig Selection - Above and Beyond %IR Purdue Corrosion Short Course February 25, 2019 Ryan Swor NACE Cathodic Protection Specialist
- 2. 2 www.LSConsulting.com Agenda Safety Moment What is DCVG Dig Selection Case Study Example
- 3. 3 www.LSConsulting.com Direct Current Voltage Gradient (DCVG) Survey What is it? • A tool that locates coating anomalies “holidays” along buried (submerged) pipelines. • Determines the relative severity of coating defects. • Can be used in conjunction with other indirect survey data for decision-making
- 4. 4 www.LSConsulting.com DCVG Survey Common Applications • Warranty work on new construction • Indirect assessment for ECDA and SCCDA processes • HCAs • Accurate location and sizing of coating faults • Recognize and locate interference from foreign structures • Locating header cable breaks • Locating CP system anodes
- 5. 5 www.LSConsulting.com DCVG Process • Current is super-imposed or the ICCP systems installed are interrupted • DCVG current is interrupted at a 25% or unique duty cycle (Commonly 1.5 seconds OFF 0.5 seconds ON) • Surveyor walks the pipeline landing a pair of probes, spaced 3-4 feet apart at regular intervals • The analog or digital meter measures voltage gradient when in close proximity to an anomaly Insert relevant photo
- 7. 7 www.LSConsulting.com %IR Coating anomalies located during s survey are sized based on the readings of interrupting voltage gradients in the earth. These gradient measurements are sized by the calculation below yielding a %IR. Coating Fault Severity %𝐼𝑅 = 𝐹𝑎𝑢𝑙𝑡 𝐸𝑝𝑖𝑐𝑒𝑛𝑡𝑒𝑟 𝑡𝑜 𝑅𝑒𝑚𝑜𝑡𝑒 𝐸𝑎𝑟𝑡ℎ 𝐶𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑃𝑖𝑝𝑒 𝑡𝑜 𝑅𝑒𝑚𝑜𝑡𝑒 𝐸𝑎𝑟𝑡ℎ × 100
- 8. 8 www.LSConsulting.com DCVG Dig Selection • Anomaly Status • Soil Resistivity and pH • Overall circuit resistance • Relative proximity of all anomalies • Depth of Cover • Coating type and conductance • Geographical and environmental characteristics • Class location • Historical records of past assessments • Polarization of the line by existing or temporary CP systems • Stray currents (AC and DC) • Proximity to foreign lines • Line features • Accessibility • Construction methods used • HVAC collocation • Other relevant survey data: CIS, Current Attenuation %IR should not be used alone as the sole dig criteria. Factors to be considered when trying to categorize potential defects include but are not limited to:
- 9. 9 www.LSConsulting.com Dig selection with CIS 0 0.2 0.4 0.6 0.8 1 1.2 1.4 10+55 10+65 10+75 10+85 10+95 11+05 11+15 11+25 11+35 11+45 11+55 11+65 11+75 11+85 11+95 12+05 12+15 12+25 12+35 12+45 12+55 12+65 12+75 12+85 12+95 13+05 13+15 13+25 13+35 On Off -850 mV DCVG Defect 100 40 20 0 80 60 %IR VDC
- 10. 10 www.LSConsulting.com Dig Selection with CIS on 2-pipe ROW
- 11. 11 www.LSConsulting.com Dig selection with FLX and HVAC collocation • %IR indicates large anomaly near foreign line crossing and HVAC powerline • Increased risk associated with AC corrosion • Verification of Anomaly on surveyed line versus foreign line
- 12. 12 www.LSConsulting.com Dig selection HDD and Depth of Cover • HDD Method for river crossing • Multiple anomalies within proximity to each other
- 14. 14 www.LSConsulting.com Case Study • New pipeline is constructed • DCVG survey completed following backfill • Based on survey findings, sites were selected for further investigation • Sites selected for excavation and direct examination (DCVG tool on site for digs) • Examination findings applied to population of anomalies • Feeds decision making for additional excavations (adding, or cancelling digs)
- 15. 15 www.LSConsulting.com DCVG Data Collected Anomaly # Signal Type Signal Status % IR Depth Analog DCVG Meter Category (Manufacturer Spec.) Notes: Selected for Investigation Hypothesis Pre-Dig Site Verification Results Selected for Excavation 1 ANOMALY 10 A/A 5% 7'2" Category 1 INSIDE STATION x Located near a weld, potential poorly coated girth weld Accessible - Inside Station X 2 ANOMALY 2 A/A <1% Category 1 3 ANOMALY 30 A/C 11% 22'4" Category 1 x Located near a weld, DS drainage ditch, potential bore coating holiday River Bore - Pipe is likely Too Deep for Excavation 4 ANOMALY 4 A/A <1% Category 1 5 ANOMALY 6 A/C 1% Category 1 6 ANOMALY 2 A/A <1% Category 1 7 ANOMALY 3 A/A <1% Category 1 8 ANOMALY 5 A/C 1% Category 1 9 ANOMALY 5 A/C 1% Category 1 10 ANOMALY 3 A/C <1% Category 1 11 ANOMALY 10 A/A 1% Category 1 hard to size due to bridge 12 ANOMALY 4 A/C <1% Category 1 13 ANOMALY 4 A/A <1% Category 1 14 ANOMALY 4 A/A <1% Category 1 15 ANOMALY 7 A/A 1% Category 1 16 ANOMALY 6 A/A 1% Category 1 17 ANOMALY 3 A/A <1% Category 1 18 ANOMALY 4 A/C <1% Category 1 19 ANOMALY 9 A/A 1% Category 1 20 ANOMALY 21 A/A 3% Category 1 21 ANOMALY TBD N/A cannot size or locate due to swamp mats X Size during site investigation No physical Access during investigation 22 ANOMALY TBD N/A cannot size or locate due to swamp mats X Size during site investigation No physical Access during investigation 23 ANOMALY 5 A/C 1% Category 1 24 ANOMALY 37 A/A 6% Category 1 x Located near a weld, potential poorly coated girth weld No physical Access during investigation 25 ANOMALY 35 A/A 6% Category 1 x Located near a weld, potential Tie-in/HDD coating holiday No physical Access during investigation
- 16. 16 www.LSConsulting.com Sites selected for excavation Anomaly # %IR Hypothesis Pre-dig Site Verification Findings 1 5% Located near a weld, potential poorly coated girth weld Accessible – inside station Scrap metal in hole near/touching pinhole coating damage 35 12% Near a T/S, potentially poor cad weld recoat T/S on road Test leads with a break in the coating on each wire 61 5% Located near a weld, potential poorly coated girth weld Behind station in sink hole Several holidays with bare steel exposed. Brushed coating was peeling off near weld. Scrapes in coating possibly due to backfill.
- 17. 17 www.LSConsulting.com Anomaly 1 – 5 %IR
- 18. 18 www.LSConsulting.com Anomaly 1 – 5 %IR • Minor coating damage on pipe • DOC – 7 Feet
- 19. 19 www.LSConsulting.com Anomaly 35 – 12 %IR • Test lead coating broken • DOC – 4.5 Feet
- 20. 20 www.LSConsulting.com Anomaly 61 – 5 %IR • Several scrapes in coating in the axial direction • DOC – 5.5 feet
- 21. 21 www.LSConsulting.com Summary • %IR Alone should not be used to select digs • Consider other data sets including, but not limited to CIS, Annual Survey Data, HVAC collocations, Depth of Cover, Accessibility, company standards and O&M • Comparison between anomalies prior to and after excavation helps with decision making for additional excavations. • DCVG is a tool that supplements other Integrity-based assessments and decision making
Editor's Notes
- With an experienced, specialized focus on five disciplines inherent to the industries we serve, Shawcor is the true end-to-end solution for an endless number of operational challenges. LSC is a key part of the Integrity Management division of Shawcor.
- With an experienced, specialized focus on five disciplines inherent to the industries we serve, Shawcor is the true end-to-end solution for an endless number of operational challenges. LSC is a key part of the Integrity Management division of Shawcor.
- Example of data collected and number of anomalies. Leads to dig selection based on accessibility, %IR, location relative to pipeline features, and findings in next slides. 61 total anomalies identified in this segment. 3 selected for excavation.