Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.
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NACE International is introducing a new way to communicate with your peers by consolidating existing member platforms into one , easy-to-use Online Communit y. Tailor your experience by choosing the g roups that meet your needs , control when you receive notif ications or updates , and ask advice and g ive feedback to peers within your indus- tr y or area of interest . The new NACE International communities are open to members now, f rom the Resources link at www.nace .org. The following questions and answers are pulled f rom the previous list ser ver archive and f rom the new Online Communit y. Please be advised that the items are not peer-reviewed , and opinions and sug gestions are entirely those of the inquirers and respondents . NACE does not g uarantee the accuracy of the techni- cal solutions discussed . M P welcomes additional comments to these items . They may be edited for clarit y. Performing Direct Current Voltage Gradient Survey on a Pipeline Close to a Power Line Q: I came across a problem when surveying a pipeline close to an overhead power line. Induced alternating current (AC) voltage on the line is ~1 V. The impressed direct current voltage gradient (DCVG) signal on the pipe is ~750 mV. When surveying the line, the needle (analog display) on the DCVG meter (input impedance 1 MΩ) stays to one side and cannot be centered using bias handles. I believe it is because of the induced AC in the DCVG meter circuit (DCVG probes and connecting leads). With the same set of equipment we are able to locate coating anomalies on other pipelines. A lso, we are able to move the needle of the DCVG meter using bias handles once the surveyor is ~100 to 200 ft (30 to 61 m) away from the power line. Has anyone had a similar situation and found a solution for it? A: Have you tried reading the over- the-ground voltage DC using two reference cells and a common voltmeter? If there is a strong gradient, this may cause you problems but I think that the AC induced voltage won't disturb your DC readings. A: I have observed the analog meter needle oscillating at a very high frequency in the presence of AC. e span of the needle movement may be 1 mm or a little more. is was right underneath a 400-kW power line. But I could move the oscillating needle from left to right using a bias probe. 13 NACE INTERNATIONAL: VOL. 56, NO. 10 MATERIALS PERFORMANCE OCTOBER 2017 THE BLOG ■ Universal corrosion resistance in extremely high temperatures. ■ Custom complex shapes in any size with tight tolerances. Visit our NEW website: http://hexoloy.com For more information, technical data & case studies contact: SCD.sales@saint-gobain.com ■ 716-278-6233 ® Eliminate Downtime & Minimize Maintenance Costs Reduce Energy Consumption & Emissions Maximize Productivity