Introduction
These circuits are used for measuring the resistance of solutions or gases to measure an ohmic IR drop through a material or solution. :R=\frac{2.303\rho}{2\pi L}\log{\frac{d}{r}}
R=\frac{2.303\rho}{2\pi L}\log{\frac{d}{r}}Where:
𝑅 − Resistance to electrolyte(ohms)
𝜌 − Electrolyte resistivity(ohm⁄cm)
𝐿 − Distance through the electrolyte traveled by current,assumed 1cm.
𝑑 − Distance from the central electrode(cm)
𝐾𝑎 − Geometry factor for the central electrode
𝑟 = 𝐾𝑎𝜌
Some commonly used electrode arrays and their geometric factors. Note that for the multiple gradient array, the total array length is ‘(s + 2) a’ and the distance between the center of the potential dipole pair P1 – P2 and the center of the current pair C1 – C2 is given by ‘ma’.
Case Guide
Part 1: Create Case
- Select the Electrolyte Resistance from Surface of an Electrode to any Distance application from the Pipeline Corrosion list.
- To create a new case, click the “Add Case” button
- Enter Case Name, Location, Date and any necessary notes.
- Fill out all required parameters.
- Make sure the values you are inputting are in the correct units.
- Click the CALCULATE button to overview results.
Input Parameters
- Electrolyte Resistivity(ohm-cm)
- Distance from the Central Electrode(cm)
- Geometry Factor for the Central Electrode
Part 2: Outputs/Reports
- If you need to modify an input parameter, click the CALCULATE button after the change.
- To SAVE, fill out all required case details then click the SAVE button.
- To rename an existing file, click the SAVE As button. Provide all case info then click SAVE.
- To generate a REPORT, click the REPORT button.
- The user may export the Case/Report by clicking the Export to Excel icon.
- To delete a case, click the DELETE icon near the top of the widget.
Results
- Resistance of Electrolyte(ohm)
References
- ANSI B31.G Calculations
- PRCI – A Modified Criterion for Evaluating the Remaining Strength of Corroded Pipe, Database for Corroded Pipe Tests and Continued Validation of RSTRENG
- NACE – Electrical Resistance and Resistivity Calculations
FAQ
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ASME B31G Original/Modified and RSTRENG?
ASME B31.G Original and Modified (0.85) are Level 1 assessment along with most other metal loss calculations that are limited to pits and short lengths of pitting clusters. RSTRENG is a Level 2 metal loss calculation; however, it is not limited just to pits, but most lengths of pitting i.e., 2500 mm (100 inches) using interaction rules that is not uncommon on some pipelines. Check Out
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Preventative and Corrective Measures to Control Corrosion Pitting?
A corrosion rate needed to set the re-inspection interval, reassess the performance metrics and their current applicability, plus to ensure the assumptions made are correct. At each direct examination where corrosion pitting is found, the operator should measure and record each pitting cluster. Check Out
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Estimating Internal Corrosion Rates?
Internal corrosion is most likely to occur where water first accumulates. Predicting these locations of water accumulation serve as a method for prioritizing local examinations. Predicting where water first accumulates requires knowledge about the multiphase flow behavior in the pipe requiring certain data. Check Out
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Estimating External Corrosion Rates?
All corrosion defects found during each direct examination should be measured, documented, and remediated as needed. At each excavation, the pipeline operator should measure and record generic environmental characteristics (such as soil resistivity, hydrology, drainage etc.). Check Out