Corrosion Prevention: Anodes, Nail-polish, and Continuity Checks

Extreme corrosion on a MicroRider-1000 after a long-term deployment with zinc anodes

Corrosion prevention is an easy to overlook, yet critical practice for operating in the corrosive environment of the ocean. Your Rockland Scientific MicroStructure instrument is equipped with one or more sacrificial anodes to prevent corrosion of your instrument. The anodes are electrically connected to the entire instrument providing protection to the instrument when submerged in seawater.

It is important to note that anode protection only works while the instrument is submerged in seawater.  When the instrument is in air, the anodes stop working and any residual sea water will cause corrosion to occur at vulnerable sites.  For this reason, it is important to thoroughly rinse the instrument with fresh water, especially when it is not active for more than 24 hours.  Before storing the instrument, it is imperative that the instrument is completely dried, as even fresh water (or dampness) can lead to corrosion if left long enough.

Zinc Anode vs. Aluminum Anode

Corrosion study with a MicroRider-1000

In 2015 Rockland Scientific’s Production Tech John Wells conducted an internal study of corrosion affecting RSI MicroStructure instruments. The key findings of the study are:

  • Aluminum anodes (mil spec. MIL-A-24779) provide superior protection and longevity than zinc anodes
  • Over time zinc anodes build a layer of oxidation that can insulate the anode from seawater diminishing its effectiveness
  • Aluminum anodes are formulated to slough off any oxidation resulting in continued peak performance. 
  • Placing a rubber washer under the anode helps prevent seawater from oxidizing the threads of the anode screw, thereby ensuring a good electrical connection. 

The study findings greatly enhanced the understanding of corrosion prevention at Rockland Scientific. If you have an instrument with an original zinc anode please ensure that the zinc is well scraped off before each deployment. Not all aluminum anodes are created equal, the study determined that a particular anode alloy formulation works best. RSI recommends that customers source their own spare aluminum anodes with mil spec: MIL-A-24779.  If you would like an aluminum anode to replace a zinc anode on your instrument please contact technical support to request a complimentary aluminum anode and rubber washer.   

Copper tab connecting the rear bulkhead to pressure tube

Consider the anode on the rear bulkhead of a VMP-250. The anode is electrically connected to the rear bulkhead by the threads of its mounting screw. The copper tab on the rear bulkhead contacts the inside of the pressure tube where the anodized layer has been intentionally removed. It is important to check that the copper tab is making a connection to the pressure tube. Overtime the copper tab can become bent and oxidized. The oxidization can easily be removed with sandpaper. You should hear and feel the tab making contact with the tube when the rear bulkhead is inserted into the tube. If you do not hear and feel the tab making contact then gently bend it back into place. You can test if the copper tab is effective by performing the continuity check described below.

 

Continuity Check

Checking the continuity between the rear bulkhead anode and a scratch on the pressure tube of a MicroRider-1000

Before you deploy your instrument, you can confirm the anode will do it job by performing a continuity check. Use a digital multimeter on the continuity (beep) setting and test for continuity between the anode and any exposed metal such as the rear sealing nut, the front sealing nut, any scratches in the black anodized layer and the connectors on the rear bulkhead. If there is electrical continuity between these parts and the anode then the anode will help protect them from corrosion.   

Nail-polish

It is helpful to have two purposes for everything you bring with you to sea. In addition to making you look your best on deck, nail-polish is effective as a paint to cover nicks and scratches on your instrument. The pressure tube has a black anodized layer that electrically insulates your instrument from seawater. This insulation helps prevent corrosion of your instrument. When the anodized layer is broken, for example from being scratched by sharp fingernails, the exposed metal will start to corrode. To prevent corrosion of exposed metal, thoroughly wash, and dry off, the damaged spot and surrounding area, then paint over with nail-polish. Black nail-polish is often used for aesthetic reasons, but many users prefer a clear polish to allow periodic monitoring of the site.      

Freshwater

Please note that while fresh water is much less corrosive than seawater, proper corrosion prevention practices should still be followed when operating in freshwater bodies. Aluminum anodes will remain effective in freshwater, however for long-term deployments in freshwater RSI recommends magnesium anodes. Please contact RSI if you would like to discuss the best option for your application.

Maintenance Tips Review

  • Rinse instrument with freshwater after each deployment
  • Ensure instrument is dry before storing for more than 24hours. Remember, corrosion never sleeps!
  • Perform post cruise maintenance and cleaning before long-term storage
  • Check electrical continuity between anode and sealing nuts and any scratches on pressure tube
  • Bend and sand copper tab on rear bulkhead if necessary
  • Paint any exposed metal due to scratching with nail-polish
  • Scrape oxidization off zinc anodes before each deployment
  • If you have a zinc anode please request a replacement aluminum anode from RSI
  • Clean the anode bolt and coat threads with anti-seize lubricant such as Never-Seez to ensure continuity between rear bulkhead and anode
  • Magnesium anodes are recommended for long-term freshwater deployments

 

Troubleshooting Realtime Instruments

Early morning deployment of VMP-2000 using a Chris MacKay hydraulic winch system aboard the R/V Point Sur, Gulf of Mexico 2017

The Rockland suite of instrumentation includes many realtime instruments including the VMP-2000, VMP-500-RT and the VMP-250-RT. Realtime instruments use an electro-mechanical cable to send data back to the ship in real time. Cables can reach lengths up to 2500m and sending data this distance is no easy task. The strength of the received signal on a communication line decreases with increasing length of the line and bit-rate. You can learn more about the transmission of data and modifying the bit-rate in Technical Note 003 available in the downloads section.

The most common issue with realtime instruments are communication errors known as bad buffers. Bad Buffers occur when a data record sent from the instrument is not interpreted correctly by the receiving computer. The data in the record is lost and the cause of the bad buffers must be investigated. Bad buffers are most often caused by damage to the transmission cable. Cables that have been damaged by anomalously large stresses, such as by bending it around sharp-edged objects, or by excessive twisting and hockling, may still show DC electrical characteristics that are nominal. However, the local discontinuity of resistance, capacitance and inductance will cause a partial reflection of the signals. A reflection reduces the amplitude of the transmitted signal. The reflected signal will probably get reflected back into its original direction of travel (by other discontinuities) and thereby skew the phase of the signal received at the far end. This skewing of phase can be very detrimental. Usually, the maximum stress on the cable is at the instrument end. If a cable, that previously worked well, exhibits progressive deterioration (an increase in the frequency of bad buffers, for example), then it may be necessary to trim off some of the cable at the instrument end, and re-terminate in order to re-establish successful communication. The amount trimmed from the cable is usually 50 to 200 m. The entire length of a cable should also be visually inspected for signs of damage, on a regular basis (such as before every cruise), by spooling the cable from the winch to a holding drum.

Directions for re-terminating (splicing) the instrument end of a VMP cable can be found in Technical Note 014 available in the downloads section.

 

CRECHE Seminar: An EM flow sensor for measuring the axial speed of gliders

An underwater glider deployed by CRECHE doing fine scale measurements near Sodwana Bay [Photo: Sean Whelan – Woods Hole Oceanographic Institute]

Many thanks to the Centre for Research on Environmental, Coastal and Hydrological Engineering (CRECHE) for hosting Dr. Fabian Wolk, the President and co-founder of Rockland Scientific Inc. (Victoria, BC, Canada), a leading developer of scientific instrumentation for ocean microstructure and turbulence measurements. Fabian presented a seminar regarding instrumentation used on robotic autonomous underwater gliders that can be used for long-term ocean deployments that measure mixing and other features of our oceans. CRECHE currently has a project doing such measurements in the Agulhas current off the east coast of KZN – the first such measurements made in this region.
 
TOPIC: An electro-magnetic flow sensor for measuring the axial speed of gliders
ABSTRACT: The axial speed of the glider, U, is an important quantity that affects the flight dynamics of the glider as well as the accuracy of certain oceanographic observations. For example, accurate knowledge of U is required when converting measurement points from time-domain spacing to spatial-domain spacing. Some sensors, e.g. turbulence shear probes, require U for proper scaling of the measured signal. While U can be estimated from hydrodynamic models, a direct measurement of the axial speed is preferred in many applications.  This presentation introduces a small current speed sensor that can be added to gliders to directly measure U to improve glider-borne measurements with shear probes.

Powering a MicroRider Instrument: Startup and Shutdown Sequence

The MicroRider is a small instrument package for turbulence microstructure measurements, designed to integrate with a variety of marine instrument carriers, such as Gliders, AUVs, moorings, CTD rosettes, profiling floats and the WireWalker.

Depending on the age if your MicroRider instrument, it will either have an IE55-1206-BCR or a MCBH(WB)-8-FS connect on the rear end-cap.  This connector serves as the power supply, RS232 serial output and ON/OFF signal for the MicroRider. 


To power on your MicroRider, here is the startup sequence:

Using the connection to the IE55-1206-BCR or MCBH-8-MP connector, where:

Pin 1: +12VDC Power
Pin 2: Power Ground
Pin 3: Not Connected
Pin 4: Not Connected
Pin 5: RS232 TX
Pin 6: RS232 RX
Pin 7: ON Signal
Pin 8: ON Signal Return
  1. Connect the Power to Pin 1 and Pin 2. This power must always be available (on and live) to the MicroRider.  The power supply board has a low power watchdog circuit that checks the power. 
  2. If the power voltage is OK (within limits) than the power supply board waits for the ON signal to be activated. 
  3. The ON signal is connected to Pin 7 and Pin 8. It is either done by shorting across Pin7 and Pin8, or by sending a small current (1mA – 2mA) into Pin 7 and return on Pin 8. 
  4. When the ON signal is detected by the power supply board it energizes the MicroRider. 
  5. The internal computer boots up. 
  6. At this time the customer RS232 connection on Pins 5/6 through a terminal program (Motocross) can be made so the customer has manual control of datalogging. Or, the computer can be set up so it automatically starts datalogging. 
  7. To safely shut off the MicroRider the customer must stop datalogging. 
  8. Then remove the ON signal which tells the power supply board to shutdown. 
  9. The MicroRider goes back to the very low power watchdog state waiting for the next ON signal. 
Basically: 

  • Power must always be available 
  • ON/OFF is controlled by the user through a shorting switch or using a small current driver 
  • Datalogging is either started automatically; or the user can manually control through the serial connection. 
  • Power must not be disconnected while datalogging or the onboard computer files will be corrupted and it will not work properly.

IAPSO – IAMAS – IAGA Conference

Dr. Fabian Wolk and Dr. Rolf Lueck will be at the International Association for the Physical Sciences of the Ocean (IAPSO) Conference in Cape Town, South Africa from August 27 to September 1, 2017.

European Wave and Tidal Energy Conference

Dr. Justine McMillan and Jeremy Hancyk will be at the European Wave and Tidal Energy Conference (EWTEC) in Cork, Ireland from August 27 to September 1, 2017.

Justine will be presenting her paper “An Assessment of the TKE Balance at a Tidal Energy Site Using ADCP and Shear Probe Measurements” at the conference.

Rockland Scientific Hires Staff Scientist

VICTORIA, BC, CANADA, July 24, 2017 — Rockland Scientific Inc. announced the appointment of Dr. Justine McMillan as Staff Scientist. Dr. McMillan will act as scientific and technical liaison between Rockland’s customer base and the company’s R&D and customer service teams.  
Dr. McMillan recently completed her doctoral degree at Dalhousie University, focussing on the measurement of turbulent flows in energetic tidal channels. Her work has been instrumental in the ongoing tidal energy resource assessments. She has also become an advocate for ocean literacy and scientific communication, and is “excited to join the Rockland team.”
“I’ve used Rockland’s instrumentation in several sea-going campaigns for my research work at Dalhousie, which allowed me to develop extensive experience in the processing, analysis and interpretation of turbulence data sets. My experience enables me to support Rockland’s customers, not only helping them get their data, but also assisting them in turning the data into research-paper-ready information”, says McMillan.
About Rockland Scientific: Rockland Scientific Inc., located in Victoria, British Columbia, Canada, provides sensors and instrument systems for ocean turbulence measurements. The instruments are either ship-deployed profilers, moored systems, or deployed from autonomous gliders, floats, or AUVs. RSI measurement systems are used worldwide in a multitude of disciplines, such as Climate Research, Renewable Ocean Energy, Coastal Management and Erosion Studies, and Fisheries Research. 

Rockland Scientific Awarded Camosun College Co-op Employer of the Year

Rockland Scientific has been awarded the Camosun College Co-op Technology Employer of the Year Award for 2016, as well as the overall Co-op Employer of the Year Award for 2016.

The Co-operative Education and Career Services department at Camosun College annually recognizes an outstanding employer in each of the program areas, and one employer across all program areas. The award is given based on the employer’s involvement with co-operative education ranging from assisting in workplace education preparation seminars to providing a co-op student with an enriching work experience. John Wells writes, when nominating Rockland Scientific:

“My time at RSI has been extremely positive and given me highly relevant experience that will be invaluable when seeking full time employment. This co-op has further validated my choice to pursue a career in Mechanical Engineering Technology by demonstrating that I have an aptitude for the work and that this type of work is in fact enjoyable and rewarding for me. Most importantly, I am confident that this co-op has truly initiated my transition from student to practicing technologist.”

Employer partners provide valuable and relevant learning that enhance the students’ success and that of the co-operative education program at Camosun. In particular, their strong mentorship of the students, building upon their strengths and encouraging their career growth throughout the technology world has proved invaluable. The award was presented by Nancy Sly, Director of Applied Learning, Co-operative Education and Career Services at Camosun College.

Rockland Scientific to present at the University of Porto Seminar on Ocean Turbulence

Rockland’s Dr. Rolf Lueck will be delivering the seminar Ocean Turbulence: Synergy between scientific advancement and technological innovation alongside Dr. Jorge M. Magalhães from FCUP (University of Porto). The seminar, organized by the Underwater Systems and Technology Laboratory (LSTS-FEUP), will take place on June 2nd, 2017, at the University of Porto (FEUP).

Robotic Ocean Turbulence Measurements at the Observatório Oceânico da Madeira

When scientists go on holiday: Rockland’s Dr. Rolf Lueck recently presented “Robotic Ocean Turbulence Measurements” as the guest speaker at the Observatório Oceânico da Madeira. The presentation focused on the measurement of micro-turbulence, the autonomous vehicles used with the instruments and their respective technological advances.