What is close interval survey, or CIS, in the corrosion world?
A CIS is a type of corrosion survey performed above ground and provides insight on cathodic protection's effectiveness on buried structures. This survey is an on-foot inspection, taking constant pipe-to-soil potentials in regular intervals, typically 2-5ft in range. This is an extremely useful procedure to gather native data, making sure criteria is "passing", finding coating defects, tracing stray current, etc.
What do I need to perform this survey?
Here's a list of items NECASSARY items/tools to complete this survey:
Data Logger: We use American Innovation's Allegro QXs and AXs. All you need is a tool that can collect the pipe-to-soil readings, or reads, and store them in a file that can be exported and interpreted for later.
Very small strand copper wire: We use Advanced Electrical for our survey wire. It's #32 gauge, comes with a sleeve to go over the spool to protect the spool from brush, come in various lengths in miles, and the customer service is great. Copper is VERY conductive and the prime choice.
Survey pack/Reader pack: These can be bought or created in-house. This pack needs to hold the wire and data logger in place as you survey.
(2) Reference Electrodes: We call these reader sticks, and we use MCMiller to obtain them. They need to be cells tall enough to walk with, have leads coming out of them to plug into the data logger and be able to walk with.
Test Lead: This just needs to be a piece of coated copper wire, with one lead being an alligator clip and the other being a banana jack to insert into the data logger. This will be very necessary to read test points along with assisting in reconnects during the survey.
Calibrated High Impedance Multimeter: This tool is useful in every single thing to ever be done in the corrosion world. If you don't have one, steal your coworker's.
Pipeline Locator: Need to stay directly above the line as much as possible. We use Radiodetection's RD7200. Amazing device!
Here's some of the equipment:
Survey pack w/ tray, reader cell, and Allegro AX.
Survey pack w/ tray, reader cell, and Allegro AX.
How can I prep for this survey?
There are some things that need to be known prior to boots on the ground. Here's some of my recommendations:
Is the line coated or bare? What type of coating?
Is the line galvanically protected or with rectifiers?
Rectifiers & Interruption (if applicable); How many rectifiers are there? Where are they? Who's installing the portable interrupters or are they RMUs?
Is there any AC mitigation on the line? If so, does it disconnected to survey or can it remain connected?
Any SSDs needing disconnected prior to the survey?
Are there any critical bonds that need interrupted?
Are there foreign utilities in the area? If so, they'll need interrupted to match your cycle or completely depolarized for native surveys.
Is there a KMZ of the line?
There's no end to questions that can be addressed prior to beginning a close interval survey. These are my personal favorite to know ahead of time. Oh wait, I forgot...the most important question is...
IS THE LINE BRUSHY OR CLEAR?!
Waveprints
You got the gear, you asked the questions to be prepared, and you took the time to get fully OQ'd and trained before heading out there. Prior to clicking that enter button, you NEED to look and obtain a waveprint of the line if possible. A waveprint shows the readings and interruption of the line. You can gain useful information from this:
This shows the interruption is in sync and all the current is getting off the line. Accidents happen; one interrupter may be starting in the wrong cycle, and the waveprint will show this. This needs addressed to obtain accurate readings.
There could be a capacitance effect on the structure:
AC mitigation or decouplers could still be attached.
Coating quality could be very old, coal tar, for instance, which may result in setting an earlier ON delay and a longer OFF delay within the waveprint settings for better potential accuracy.
I was surveying once, and the client instructed me all AC mitigation was disconnected. I checked the wave, and I noticed a shark fin looking graph. This is a dead giveaway a CP source is still connected. The reason for the shark fin:
Once the interruption is cycling OFF, there is a CP source somewhere still connected giving the line CP.
You can tell is a reference cell is shorted. A shorted cell will cause the readings to go all over the place. Jiggle around the wiring and tap on the cell from top to bottom to ensure no shorting.
How do I begin?
Once you’ve gathered all your materials and equipment, got all interruption set, it’s time to begin the hard work:
Before putting on the survey pack, mount the survey wire spool on the back of the pack. Once mounted, have a coated wire (preferably #10 or so) running from the inner connection of the spool, the pig tail, to the front tray of rhe pack where the data logger is mounted.
Put on the survey pack and mount the data onto the tray coming off the front of the pack.
Verify both reference electrodes are within a threshold of calibration.
At RCS, we plug one reference cell into the positive port of a calibrated multimeter and the other into the negative port on the meter. We turn the meter to mV DC and touch the two porous tips of the electrodes together. Every company has different requirements, but we aim for 3mV or less in calibration. This ensures when both cells are used for CIS, there's a MAX 3mV discrepancy between the cells.
Connect both reference cells into the negative port on the data logger. Plug the three prong attachment coming off the electrode into the corresponding receiver on the data logger. This allows the surveyor to click the buttons mounted on the top of the survey cells to collect readings instead of manually pressings ENTER. • I use electrical tape on the banana jacks of the electrodes to ensure they don’t come disconnected as I survey.
Now it’s time to find the starting location. This could be a test station, valve, riser, IFL, whatever the designated “start” is.
At the starting location, use your test lead, plugging it into the positive port on the data logger, and clip onto whatever you’re starting at. It’s time to verify readings and collect a waveprint to ensure the system is ready to be surveyed. • If you’re starting at a coated piece of pipe, look for a stainless steel grease fitting or any other invested piece on the structure.
Once everything is verified, strip and connect the other end (unused side) of the survey spool wire onto the starting location. Remove the test lead and plug in the #10 wire ran from the inside wiring of the survey spool to the positive port, Ensure the data logger is receiving correct and accurate readings.
If everything matches in and there’s no issues, place the first reference cell of your choice 2.5ft, or whatever your interval spacing is, in front of you. Using the button on the cell, collect a potential.
Have whoever is lucky enough to have the pipeline locating job to locate the structure ahead of you to keep you center of the structure.
Repeat these steps in systematic order until you come up to another structure or test point on the line or the end of the line. • If you come across another test point or structure, it’s CRUCIAL to obtain an MIR, or reconnection. • A reconnect ensures all current is coming off the line, verifies you’re still on the correct structure, and can help track current if there is any still on the line.
Last, but not least, make sure to note, or key in, every obstacle, road, line marker, fence….just everything you can into the data logger. It’s always safe to have too many comments/remarks than not enough.
(my reference cell button broke, so I had to manually press enter, but you get the idea)
Quick Notes & Tips:
Asphalt, concrete, and other extremely dense, thick materials are very difficult to obtain accurate readings. You may have to drill through or skip the pieces, if applicable, and continue with the survey. Consult with your company to ensure you’re doing everything correctly.
Piping inside casing vents and through horizontal direction bores are extremely difficult to accurately collect readings from while surveying directly on top of them. They will have to be skipped if allowed.
Always collect readings in places that are free of debris. For instance, don’t read on top of rocks, huge leaf piles, straw matting…you get what I mean. Water packs may be needed in dry conditions.
What are some obstacles I can run into?
Obstacles vary in all situations, but they’re nothing to be nervous or scared about. Some obstacles are the following and how to overcome them:
Fences: Survey up to them, and try to crawl under, if possible, or look for an entry/exit gate or door nearby. Walk around to the going away directly across where you surveyed up to.
If the fence is electric, and you crawl under the strands, I highly recommend tying the wire around grass, rocks, or any other debris to avoid it flinging up onto the electric strands. This could cause significant harm to you and the equipment.
Creeks, rivers, lakes, or even the ocean: Treat these situations just like fences, but you will include a skip if necessary. Survey up to the edge as close as you can, and if the creek is impassible, begin a skip in the comment section of the data stream. Find a way around the body of water upstream or downstream and go directly across where you began the skip. End the skip on the opposite edge of the water, and continue.
Sometimes bodies of water have no safe passage around. This happens, but don't worry. Survey up to the edge, collect your final readings and waveprint, save and end that file. Walk out and find a way to the opposite side of the body of water. Connect to a test point somewhere downstream of the line, walk back into the going away side of the body of water, create a new file, and continue the good fight.
Asphalt roads: Unless it's recently been a monsoon or you're drilling through the asphalt, the chance of obtaining accurate readings is very, very slim. Survey up to the edge of the coming in side of the road, key in the road name, tie your wire down around rocks or any sort of debris to keep it tight and flat to the road, and safely cross the road. Once on the going away side, tie down the wire in the same fashion, key in the road name, and end the skip. Continue with the survey.
There are road spools manufactured by companies specifically for crossing roads. They are made of a heavier gauge wire, on a reel spool, with two separate connection points that allow the wire to not break on the busy road. This allows a survey to hook up their CIS wire to one point on the road spool, lay the road spool wire tight across the road, and connect the survey wire onto the second connection point across the road.
When in doubt of an obstacle, always consult your team, manager, or whoever you can to safely come up with a gameplan moving forward.
What can be done with all the data collected?
Once you've walked all the grueling miles and endured "the suck," you will have a data logger gushing with data. You can process the data and plot everything that's been collected. Once everything is plotted, it's time for interpretation:
Where exactly low and high spots are on the line
Interference areas
High risk corrosion areas
Be able to accurately represent passing data per your company's spec
Close interval surveys aren't glamorous. It's raw data collected by boots on the ground enduring rough terrain, inclement weather, and long days to adequately obtain pipe-to-soil measurements to determine CP's effectiveness. It's a very rewarding experience. A technician gets to see CP systems firsthand, and they get to see what goes wrong and why it's happening. They're problem solvers and have to be able to adapt quickly. People who have completed or been involved in a CIS make the best technicians.
As always, let me know if you have any questions, concerns, or want to follow up on anything in the article.