There’s been questions of late on OB social media about what was happening next to the AutoZone on Santa Monica.
Finding myself on Santa Monica Ave on Thursday across the intersection from a small fleet of trucks, drilling equipment and workers clad in white suits next to the AutoZone, I jaunted over and made some inquiries.
Some workers were mixing and pouring what at first looked like mud but turned out to be carbon particles down a hole in the street (I couldn’t actually see the hole) – and this curious scene needed an explanation, I thought.
At first I asked a couple of the workers, guys driving trucks or operating equipment, what was going on; they declined to tell me – and pointed me in the direction of somebody that could.
A guy with a white hardhat with SDG&E decal approached – we had to move off to one side nearly to the sidewalk and away from the noise to talk.
It was indeed a San Diego Gas & Electric project; they had hired NRS Environmental Services to do the actual work. And they were drilling – but for what?
“We drilled down 200 to 300 feet,” the guy from SDG&E said.
“Wow,” I responded, “you must have hit seawater.”
“Not at all,” he said.
And then I asked what they were doing, and why they were drilling down so deep.
His answer – I had to ask him to repeat it several times – was something I cannot really explain or describe. He kept saying, “look it up on the internet,” – which I’ve done, and I still cannot explain it.
But basically, it’s a procedure to stop corrosion of steel cables, electrical lines. It’s highly scientific – and one needs an engineering or chemical degree to understand it.
Potentially – something like this diagram is going on below the surface in OB. Graphic from “Corrosion Protection of Metals”
It’s all about being a method of combating corrosion which is actually widely used : it’s called cathodic protection. And it’s one of a couple methods which depends – according to a scientific paper on “Corrosion Protection of Metals” –
“… on controlling the charge on the metal surface, and this can be monitored by measuring the potential of the metal. The conditions needed to stop corrosion can then be predicted from an electrochemical phase diagram.
Cathodic protection is effected by forcing the potential to a negative region where the metal is completely stable. This can be done by using a sacrificial anode made from a more reactive metal, or using an external power supply to change the amount of charge on the metal surface. Cathodic protection is well suited to steel structures in marine or underground environments.”
See what I mean.
Actually, similar things are done to boat hulls.
In the case of this project in OB – which was to be just a 2-day project, Wednesday and Thursday – they’re using the carbon “mud” to spread the charge out over a wider “field”. Don’t ask me to explain this more.
“Where’s the actual steel cable?” I asked.
The SDG&E guy pointed off to the northeast. “It’s over there,” like in blocks away in the alley.
It just got more confusing for me.
So, that’s it, facebook. They’re not drilling for oil – or water. They’re drilling to squish a bunch of carbon down a long hole to provide a wide area for the electrical charge that will prevent the steel cable from corroding. Understand?
{ 10 comments… read them below or add one }
Really would like Stu or Geoff or Frank Florz or somebody to explain this more. Me, I have a sociology degree and doctorate of law – and it’s over me.
Well Frank, none of this makes much sense to me and I’m not being critical. I am familiar with cathodic protection and I think you explained it well enough. Metal pipe underground can corrode quickly in corrosive soil, that is it can carry an electrical charge that eats away at the pipe. An anode is attached as a sacrificial metal, usually zinc. For some projects, the anode is in a surface box and connected to the underground pipe with a wire. The zinc is sacrificed instead of the metal pipe and it literally is eaten away as it draws the charge to it and away from the pipe. This is similar to galvanizing that people are more familiar with. The galvanized coating is usually zinc and it protects the metal under it by corroding first. These anodes are replaced on a regular basis. And, you are correct, a similar system is used on boats due to the electrical charge caused by saltwater, movement I believe, and the metal parts exposed to the water.
What I don’t get is the “steel cable” thing. I did a lot of underground work including electrical and never saw a buried “steel cable”. Electrical cables are not usually direct buried but are in conduit. And, the cable that is direct buried is coated to protect it from moisture. There is steel inside the cable.
Drilling down that far also doesn’t make sense to me, there are no utilities that deep.
I’ve never heard of this method and can’t find anything on it by Googling. I can’t find a website for NRS Environmental but what little I did find was that it specializes in environmental cleanup. Methinks there is more to this story. This smells more like some kind of clean up to me.
Geoff has the same questions I do. The guy’s excuse sounds right. But it doesn’t take into account n un-shielded cable buried 200 foot deep. Those are the kind of depths used to engineer hydro-electric dams – not something you’d find in OB.
I’m pretty sure that if y’all search for “Conductive Carbon Grout” (the mud of which Frank speaks) the commercial product descriptions will explain a lot.
This process is used to prevent corrosion when the environment is salty, moist soil. SDG&E does this in Oceanside a LOT.
…as I understand it they are protecting conduit (running under the alley, and nowhere near 20 feet deep, let alone 200) by constructing a vertical Anode: sinking a steel sleeve and filling it with this conductive grout . . . 200 feet deep.
It’s probably not the electrical but the Natural Gas pipes. Most of the old high pressure piping is steel, and not galvanized since zinc can react with petroleum products.
I concur. They do the same procedure to maintain the HP Gas line that runs down the LOSSAN Railroad corridor outside of my bedroom window.
Well, I typed a comment earlier in the day but it didn’t seem to go through. I just wanted to thank Peter for the information, it is interesting. And I also think that Micah is correct, gas lines do need this protection so that sounds right to me.
The 200-300 foot bore hole isn’t to reach a pipeline or whatever they are trying to protect, but, to provide space for enough anode material, sounds like they are using graphite, to work over a long period of time. (The mud is probably just drilling fluid to lubricate the drill bit and force the cutting up out of the hold). The graphite will eventually be consumed (or more accurately transferred to the cathode i.e. the thing being protected), so, you need to have enough to last for a while to avoid doing this again any time soon. 200 to 300 foot bore hole sounds about right for at least 30 years of protection. Since the anode material is connected to a junction box and then connected to the cathode via electrical cable the bore hole containing the anode doesn’t necessarily have to be real close.
MOre good information, Toolpusher, thanks for that.