Buried cross-country pipelines are protected from corrosion by impressed-current cathodic protection (CP), and modern standards increasingly expect that protection to be monitored remotely. A remote monitoring unit (RMU) measures the rectifier's AC and DC voltage and current, the pipe-to-soil potential, shunts and bonding currents, synchronises global CP interruption surveys by GPS, and reports over cellular or satellite from sites that often have no mains power. Running such an instrument from a small solar panel and a rechargeable buffer - where sealed nickel-metal hydride has specific advantages - is the subject of this paper.
ISO 15589-1:2015 governs cathodic protection of on-land buried pipeline steel and, in its current form, recognises remote monitoring as an option for tracking CP parameters; EN 12954 sets general CP principles, EN 13509 the measurement techniques and criteria, and NACE SP0169 (now part of the AMPP standards family) the control of external corrosion. Together they define what an RMU must measure - rectifier output, pipe-to-soil potential against a reference electrode, current through shunts and bonds - and how those readings are interpreted.
Commercial RMUs such as the MOBILTEX RMU1 and satellite Bullhorn-style units are specified for multi-year battery life (a representative battery interval near five years for a non-solar unit), while solar-powered product families sustain continuous monitoring by pairing a panel with a rechargeable buffer. The instrument is remote, weather-exposed and often extremely hard to visit, which makes power reliability a corrosion-safety issue, not just a convenience.
The first animated figure traces the RMU's current across a day. On a schedule of fifteen minutes to an hour it wakes and excites several analog channels - reference-electrode potential, DC voltage and current, sometimes AC interference - a measurement that takes seconds of milliamperes. For synchronised interruption surveys it acquires a GPS fix (a seconds-long, relatively high-current event shared by every RMU on the pipeline at the same instant), drives the interruption relay, and captures the instant-off potential. It then transmits over cellular or, in remote right-of-way, satellite - a high-current burst, especially for satellite, which can draw an ampere-class pulse during transmission.
A solar installation charges the buffer through daylight hours, while a non-solar unit depends entirely on a primary battery sized for years. In both cases the instantaneous peaks - GPS, relay, satellite PA - are far above the long-term average and set the pulse requirement.
The second figure shows autonomy versus buffer size for cellular and satellite reporting: because each satellite contact is energy-expensive, a non-solar primary battery is forced into infrequent reporting, whereas a solar panel with an adequate rechargeable buffer supports frequent synchronized surveys and multi-channel logging with several days of reserve for overcast winter weather. The buffer must accept irregular charge, hold reserve across cloudy days, and deliver the ampere-class satellite pulse on demand.
Sealed NiMH is well matched: it charges opportunistically from a modest panel, delivers high pulse current from a flat low-impedance plateau, cycles daily for years across the instrument's life, discharges reliably in the cold of a northern pipeline right-of-way, and uses an aqueous chemistry that is safe in a sealed, weather-exposed enclosure with no thermal-management burden.
Close-interval and instant-off CP surveys require every rectifier and RMU along a pipeline to interrupt the CP current at exactly the same GPS-synchronised instant so that the pipe-to-soil 'instant-off' potential can be measured without the IR drop. That means every RMU must wake, acquire a GPS fix, be ready at the synchronised second, drive its relay and measure - simultaneously, regardless of when it last saw the sun. The buffer therefore has to guarantee the GPS-plus-relay-plus-measurement pulse at dawn after several cloudy days and in the cold.
This is a pulse-power requirement layered on top of an energy-reserve requirement, and it punishes any chemistry that sags under load: a failed GPS lock or a drooping relay at the synchronised instant produces a gap in the corrosion survey that may not be discovered until the next site visit.
The radio choice reshapes the power design. Cellular modules attach for seconds at a few hundred milliamperes and are efficient where coverage exists; satellite terminals (for lines through desert, tundra or forest with no cellular coverage) transmit shorter but much higher-current bursts and need a clean, stiff supply to complete the contact. NiMH's low internal resistance is particularly valuable for the satellite case, where a high-impedance primary cell may fail to complete a transmission at low temperature.
Where mains is available at a pump station or rectifier post, the NiMH pack acts as a float-ready DC-UPS that rides out mains loss and keeps the RMU logging and alarming; off-grid, it acts as the solar buffer described above.
The design brief records the analog channel count and excitation time, the measurement interval, whether GPS-synchronised interruption is required and how often, the cellular or satellite radio profile and peak current, the solar-panel rating and required autonomy days, and the site temperature range. Paper B turns these into an energy budget and a buffer sizing; Paper C maps the design onto the CP standards, environmental and the cell-level evidence.
Weijiang Power manufactures sealed nickel-metal hydride cells and solar-compatible buffer packs for cathodic-protection remote monitoring units and pipeline telemetry. Send us your analog channel count, cellular or satellite radio profile, GPS-synchronisation requirement, solar-panel size and remote-site temperature range, and our engineers will design a welded, wide-temperature NiMH buffer with charge management and protection. See formats on the products page.
