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Cathodic Protection - Galvanic ProtectionHowever, standard minus 1.5 volt magnesiumanodes are more generally used in the propaneindustry because they work best in themajority of underground conditions found inthe United States.The purpose of the magnesium anode is toprotect the tank and connected steel piping byproviding current and electrons to the entiresurface area of both.2.1In doing this, the anode acts like a light bulb,lighting up the surface of the steel tank.This happens because electrons flow from theexternal magnesium anode along a wire to thesteel tank the cathode. At the same time, asmall electric current measured in milliampsflows through the earth from the magnesiumanode to the steel cathode. By using naturallaws and processes where electric current flowsfrom a high voltage source to a lower voltagereceiver, man-made anodes of higher voltagemetal such as magnesium will artificiallyprevent lower voltage metal like steel fromdecomposing. The electrons actually preventthe iron atoms in the steel from oxidizing intorust. And if enough electrons flow from ananode to the tank, it will not corrode, becausethe voltage of the tank will change.8

Cathodic Protection - Galvanic ProtectionThis voltage can be measured with a voltmeterand a copper sulfate electrode.Although different metals have differentvoltage readings, the voltage reading of steel isnaturally around minus 0.50 volts.2.1A voltage of minus 0.50 volts on a propanetank would indicate that the tank isunprotected and is susceptible to corrosion.9

Cathodic Protection - Galvanic ProtectionTo avoid corrosion, the electrons must shiftthe voltage of the steel to a minimum of minus0.85 volts or more. The rule is the higher thevoltage, the better. However, the electronsshould not shift the voltage above a minus2.00 volts.2.110When a tank is totally protected fromcorrosion, it means that the entire tankhas become a cathode. The length of theprotection measured in years is dependenton the severity of the environment in whichthe tank is installed. If the tank is installedin non-corrosive dry sandy soil, it may berelatively free of corrosion and the anode willlast a lifetime. However, if the tank is installedin wet, fertilized and sticky clay like under alawn or flowerbed, the anode could possibly beconsumed in less time.

Cathodic Protection - Galvanic Protection2.2 Pre-Installation PreparationBut remember, before you do any digging, firstrefer to your company’s policy, or call the nationalhotline (811) or your local one-call system toprevent damage to underground structures.Although there are several locations where ananode can be placed, one way is to dig a holeso that the anode can be placed below thebedding of the tank. If two anodes are beingused, you’ll dig two holes.2.2Another way is to place the anode beside the tank.Again, if two anodes are being used, one can beplaced on each side or each end of the tank.When installing two anodes, they can also beplaced diagonally from each other at the endsof the tank.11

Cathodic Protection - Galvanic Protection2.3 Installation Procedures2.3The first thing is to remove the outer box orplastic bag from the anode. The anode shouldbe wetted. One good way to wet the anode isto place it in a bucket brought to the jobsiteand then fill the bucket with water. The ideais to let the anode soak up the water. It willdo this because the anode is packaged in abag of gypsum, sodium sulfate and bentoniteclay. After a couple of minutes, turn the anodeupside down in the bucket so it soaks up theremaining water. Another way to wet the anodeis to pour water over it from the container. Justmake sure you get it good and wet and that thewater soaks in. This procedure ensures moistureretention and good soil contact. That way theanode will work more evenly.Once the anode is placed in the hole, unwindthe wire and temporarily anchor it to the topof the hole with a dirt clog or rock. Then coverthe anode with dirt from the hole.12

Cathodic Protection - Galvanic ProtectionRun the anode wire to the connecting lug ortank lead wire and make the connection with asilicon filled underground wire connector. Thisis where the manufacturers have made the jobeasier. There are no more Thermite welds thatformerly needed to be performed.The integrity of the tank coating is one factorin the success of the Cathodic Protectionsystem Once the tank has been set, make sureyou’ve touched up any damaged areas on thetank that happened while loading, in transit,or unloading at the job site. Tank fabricatorsand coating manufacturers supply touch-upkits that are easy to use. Use a piece of coarsesandpaper to rough up the area around theding. Wipe the area clean with a dry clothand then apply the coating per manufacturer’sinstructions. Doing this puts less of a drain onthe anode.2.3In desert or semi-dry parts of the country,and after the tank has been set, anodes shouldstay wet so that you get acceptable results onthe tank-to-soil test. One way to do this is toplace a two inch diameter, five foot long plasticpipe, or any kind of flexible tubing into thehole next to the anode. Keep it upright whilethe hole is being partially backfilled. Afterthe tank has been buried, the top of the pipeshould extend a few inches above the ground.In order to keep what ground moisture there isfrom evaporating through the pipe, place a capon the pipe.13

Cathodic Protection - Galvanic ProtectionOnce the installation is complete, you’ll wantto document it for future reference. Followyour company’s policy and local codes, butremember, in snowy climates, NFPA 58requires the tank location to be marked.2.314

Cathodic Protection - Galvanic Protection2.4 Electrical IsolationWhen metal pipe like steel or copper is used,electrical isolation becomes critical. All metalshave a unique voltage stored within them.Bare copper lines must be isolated from thetank at the outlet of the regulator on the tankto prevent anodes from having to supply moreelectrical current than necessary to protectthe tank. Care must be taken to isolate barecopper lines from metallic tank domes or thesteel of the tank.2.4Black iron or steel lines may be protectedusing the same anode that protects the tank,but must be isolated from the building beingserved to prevent the anode from supplyingelectrical current to protect everything that’sunderground at the building that is not apropane pipe.15

Cathodic Protection - Galvanic ProtectionA dielectric union may provide the necessaryisolation. Without a dielectric union to isolatethe tank from bare pipe, or insulation toprevent a bare copper tubing from touchingthe tank through a metal dome, the currentcan collect on interconnected undergroundcopper and steel pipe that connects acustomer’s well casing or the city water systemand the electrical grid. This unwanted loss ofcurrent is like having the cathodic protection“light” illuminate all the unwanted previouslymentioned structures.2.416

Cathodic Protection - Galvanic Protection2.5 Testing EquipmentChecking your cathodic protection system isvitally important. It’s easy and takes just a fewmoments.All you need is a voltmeter and a coppersulfate electrode to measure the voltage orstored energy surrounding the tank and itspiping.2.517

Cathodic Protection - Galvanic Protection2.6 Tank-to-Soil Potential TestsFirst, if the ground is dry where you’re goingto take the readings, moisten it with water.Also, make sure the electrode has beenproperly maintained per the manufacturer’sinstructions.2.6Next, set the voltmeter on the 2 volt DC orthe 20 volt DC scale.Then connect the voltmeter to the tank, withthe positive lead connected to the multivalve ,and the negative lead to the copper electrode.Do this at the multivalve rather than thedome. While many newer domes are madefrom a poly/plastic type of material, evenif the dome is metal, it might be loose andyou probably won’t get a good reading. Themultivalve is well connected to the tank, andregardless of whether there is brass, steel or anyother metal on the valve, the important thing isthat it is a metal to metal connection betweenthe voltmeter and the tank.18

Cathodic Protection - Galvanic ProtectionThen take a couple of steps to the side of the tankopposite the dome. You’ll want to be just abovewhere the side of the tank is underground. Stickthe tip of the electrode into the ground where youhave moistened it, and take your reading. Recordyour data according to company policy. Repeatthe process on the opposite side of the dome, andthen at both ends of the tank. It is important totake four tank-to-soil potential readings around atank to get a complete picture of the cathodicprotection level. It is possible to record a goodreading above -0.85 volts on one end or one sideof a tank and have a bad reading below -0.85volts on the opposite end or opposite side of atank. When this happens, the areas of the tankthat have readings above -0.85 volts are protectedwhile an area with a reading below -0.85 volts isnot protected and could still suffer corrosiondamage. A single reading would not detect anarea of low protection . And remember, you’llwant to record all four readings. This informationcan be valuable for future reference.2.6The voltage reading on a healthy tank shouldbe equal to or greater than minus .85 volts. Thevoltage of an anode should be at least minus1.5 volts. The voltage of an unprotected tank isusually around minus .50 volts. When the anodeis connected to the tank, the two voltages averagesomewhere in between. If the average voltage ishigh or close to the voltage of magnesium, -1.50volts or higher, this indicates the tank’s coating isgood. If the voltage is low or close to the voltageof steel, there may be any variety of problemswith the tank or installation. Perhaps the anodewas not connected to the tank properly. If the copperanode wire does not make good strong metal-tometal contact with the tank, the reading couldbe low. Another possibility for a low reading isthat the electrode was not making good contact withthe earth. Additional reasons might be the rubberboot was not removed from the electrode. The batteryin the voltmeter was dead. The electrode and theconnection to the tank were not good. Or, the anodehas been consumed and needs to be replaced.19

Cathodic Protection - Galvanic Protection2.7 Troubleshooting and RetrofittingWhen a reading at an existing installation iszero, you’ll have to do some troubleshooting.The following is a laundry list of things tocheck when troubleshooting.2.71. Start with the voltmeter. Is it on?2. Is the battery good?3. Have you taken off the rubber boot on thecopper sulfate electrode?4. Have you set the voltmeter switch to thed.c. volt scale?5. Have you connected one lead wire to thecopper sulfate electrode?6. Have you connected the other lead wire tothe multivalve securely?7. Does your copper sulfate electrode have ablue liquid in it?8. Have you set the electrode firmly on theground?9. Have you poured a glass of water on theground if the ground is dry?10. Are your lead wires and their 0-0.30-1.10-0.20-1.00-0.10-0.90-0.0-0.85

Cathodic Protection - Galvanic ProtectionIf everything you’ve checked is okay, and the meter reading is below -0.85 volts, thethe meter isreadingis below-0.85Butvolts,thefollowinga secondchecklist.remember,not all of these items are going to be offfollowingis samea secondchecklist. But remember,markat thetime.not all of these items are going to be off markat thetime.is there copper tubing leading from the regulator?1.In samethe dome,1. IsIn therethe dome,is thereorcoppertubingleading2.a dielectricinsulatingunionbetween the copper tubing and the tank?from the regulator?2. Is thetherea dielectricinsulating3.coatingon theortankpeelingunionoff or non-existent in the dome?between the copper tubing and the tank?3. Is therethe coatingthe tankor4.a steelonservicepipepeelingand no offdielectricunion in the piping at the building?non-existent in the dome?4. Is there electricala steel servicepipe andno the multivalve and the pipe into the building?5.continuitybetweendielectricthepipingat the setting and a jumper wire between the multivalve Checkthisunionusingintheohmsresistancebuilding?and the pipe at the building. A reading less than 20 ohms indicates there is continuity5. Isbetweenthere electricalbetween thethe tankcontinuityand the building. multivalve and the pipe into the building?Checkthis wireusingmaythe notohms6. The anodeberesistancesecurely connected to the tank.setting and a jumper wire between theand havethe pipethe building.A its plastic bag.multivalve7. The anode maybeenatburiedstill insidereading less than 20 ohms indicates thereis continuitybetween8. The anode maybe dry.the tank and thebuilding.6. The anode maywire bemaybehavesecurely9.oldnotandbeen consumed.connected to the tank.7. The anode may have been tooburiedstill(1 lb, 3 lb, 5 lb. anodes are too small).10.smallinside its plastic bag.8. The anode may be lyingdry. up against the opposite side of the tank.11.9. The anode may be old and have beenconsumed.12. Isthere a plastic liner under decorative rock or bark between the electrode and the10. The anodehavebeen holetoo smalllb, 3 and pour water at the hole before takingtank?If so,maypuncha smallwith a(1pencillb,lb. anodesare too small).the5readingagain.11. The anode may be lying up against theoppositeside of thetotank.13. Areyou connecteda metal dome and not the multivalve ?12. Is there a plastic liner under decorative ro2.721

Cathodic Protection - Galvanic ProtectionIf everything checks out that you can see, theground is moist and your readings are stillbelow -0.85 volts, try this.2.7Take an anode out of its protective plastic bagor box, lay it on the ground next to the tank,pour water on the anode and let the water flowonto the ground.Using a 12” jumper wire with alligator clips oneach end, connect one end to the multivalve and the other end to an anode wire. Thevoltage readings on the tank should startto increase in the direction of -0.85 volts.If the voltage readings do not change, youcould disconnect a copper service line at thefirst stage regulator inside the dome. If thetank-to-soil voltage readings immediatelyjump above -0.85 volts, you need to install adielectric union inside the dome. If the voltageslowly increases, you can now think aboutretrofitting the tank by adding a new anode.If you need to retrofit an existing tank, beforeyou do any digging, refer to your company’spolicy, or call the national hotline (811) oryour local one-call system to prevent damageto underground structures.22

Cathodic Protection - Galvanic ProtectionFirst, verify there are no sprinkler lines, lowvoltage electric wires, the propane service lineor other owner installed bulbs or wires whereyou plan to dig.Cut out a plug of grass five feet to the side ofthe dome with the shovel and set it aside.2.7Dig a vertical hole at least 3 ft. deep. If thisisn’t possible, you may have to lay the anodedown horizontally. In dry environments, theanode may work better if it is laid horizontallyin a ditch 18 in. deep where sprinkler or rainwater will wet the anode. As stated earlier, ifthe tank is in a desert environment, set a PVCpipe in the hole with the anode so that watercan be poured into the pipe to wet the anode.23

Cathodic Protection - Galvanic ProtectionPlace the anode in the hole and pour water on it.2.7Touch the anode wire to the multivalve while taking a tank potential reading. Thereading should be above -0.85 volts. If so,continue with the installation. If the reading isstill not good, refer to the troubleshooting liston page 21.With the shovel, wedge the grass apart fromthe anode to the dome, and push the wiredown below the grass into the dirt.24

Cathodic Protection - Galvanic ProtectionWith a portable electric drill, drill a holethrough the dome and insert a rubber grommet in the hole.Then, push the wire through the hole into thedome.2.7Connect the wire to the tank at the studunder the multivalve , or to the riser pipeusing a band clamp. Any water proofed secureconnection between the anode wire and theriser pipe or multivalve will cause the tankpotential readings to shift to the protectedlevel of -0.85 volts or greater.25

Cathodic Protection - Galvanic ProtectionFill the anode hole with the dirt removedduring digging and use the shovel handle totamp the dirt around and on top of the anode.This fills in the voids between the anode andthe hole you dug. If you don’t do this, therewill be a gap between the anode and the holethat the current can not flow across. This willreduce the amount of current your anodecreates, and cause the readings to be lowerthan what is possible. Replace the plug ofgrass on top of the anode hole and push theseparated grass back together where the anodewire was run.2.7Once you’ve completed these steps, one lastmajor thing to do is to take a tank to soilpotential test. This was covered on pages18-19 of the manual. Remember though totake four readings, one on each side of thetank and one on each end, with a healthyreading being any voltage equal to or greaterthan minus .85 volts. But in the unlikelyevent that one anode does not increase thereadings to a protected level of -0.85 volts orgreater all around the tank, install a secondanode on the opposite side of the tank.And just like the original installation, oncedone, you’ll want to document your workfor future reference. Follow your company’spolicy and local codes.If after following all these procedures andyour reading still does not increase to -0.85volts or greater, it is possible the container istoo corroded and may need to be removedfrom service. Check with your supervisor forcompany policy regarding these guidelines.26

Cathodic Protection - Galvanic Protection2.8 Gas Piping ProtectionThe following are general recommendationsfor protecting lines connecting undergroundtanks to buildings or gas utilization equipmentsuch as generators. These recommendations arebased on commonly accepted installation codesand good operating practice. Any deviationsshould be with the recommendation of acorrosion specialist and approval of theauthority having jurisdiction.Coated Steel or Black Iron Pipe – The anodesinstalled to protect the tank will also protectcoated steel or black iron gas lines where adielectric union is installed at the building orgas utilization equipment.2.8Coated Copper Tubing – The anodes installedto protect the tank will also protect coatedcopper gas lines where a dielectric union isinstalled at the building or gas utilizationequipment.Uncoated Steel or Black Iron Pipe Uncoated steel or black iron piping is notrecommended. NFPA 58 and good installationpractices requires black iron or steel pipe to becoated.Uncoated Copper Tubing - Becauseuncoated copper tubing does not presentcorrosion problems in most soils that canresult in reduced anode performance andlife, this material must be isolated fromthe underground tank being cathodicallyprotected. Use of uncoated copper tubingis dependent on local soil conditions andapproval of the authority having jurisdiction.27

Cathodic Protection - Galvanic ProtectionCoated Steel or Black Iron Pipe WithUncoated Fittings - Uncoated fittingsshould never be used with coated black iron orsteel piping. All pipe fittings must be coatedand wrapped before burial.2.828Since coatings, pipe sizes, composition andlengths vary from one job to another, the-0.85 volt criterion will determine whetherone anode or multiple anodes are needed toachieve protection. Multiple readings over andalong a pipe may be needed to confirm thata single anode is protecting the gas line fromthe tank to the building.

Impressed Current Overview3.0

Cathodic Protection - Impressed Current Overview3.1 Impressed Curr

The Propane Education and Research Council (PERC) is a non-profi t 501(c)6 trade organization authorized by the Propane Education and Research Act of 1996 (PERA), Public Law 104-284. PERC was created “to enhance consumer and employee safety and training, to provide for research and development of clean and effi cient propaneFile Size: 2MB