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4.2.10. Installing Corrosion Protection Systems for Underground Tanks & Metal Distribution Lines.

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slide1

4.2.10

Installing Corrosion Protection Systems for Underground Tanks & Metal Distribution Lines

It is important for propane gas service personnel to understand the causes of corrosion on metal structures so that they can identify methods and apply procedures used to protect metal structures from corrosion.

  • In this module you will learn to identify:
  • Causes of corrosion
  • Methods and procedures used to protect metal structures from corrosion
  • Procedures for installing anodes and testing cathodic protection systems
slide2

Identifying Causes of Corrosion

Corrosion is an electrochemical reaction between a metal and its environment.

This damaging reaction occurs between the metal surface on the underground ASME tank and the soil that surrounds it.

Corrosion will also affect buried metallic distribution piping.

slide3

Methods Used to Protect Buried Tanks

Coatings— Specially formulated coatings protect buried tanks and metal pipe against corrosion.

Manufacturers typically coat underground tanks as part of the manufacturing process to ensure a long and safe life of the buried tanks.

Because tanks may be damaged during transport or installation, additional coating may need to be done at the plant or customer location to repair “holidays”. (A holiday is a void in the protective coating that exposes the metal surface of the tank.)

slide4

Methods Used to Protect Buried Tanks

Requirements for Properly Applying & Maintaining Tank Coatings

  • Properly Cleaned Surface
  • Proper Priming and Coating Materials
  • Proper Application of Coatings
  • Proper Handling and Storing of Materials
  • Proper Handling of Coated Surfaces
  • Thorough Inspection and Repair of Holidays

Pipe and tank coatings provide the principle and most effective deterrent to underground tank and steel pipe corrosion. A properly manufactured and applied coating will serve to provide approximately 99% of the protective needs of buried metal structures.

slide5

Methods Used to Protect Buried Metallic Pipe

To protect pipe, apply a protective coating of pipe wrapping tape that has an adhesive side compatible with pipe coatings to cleaned pipe surfaces. Wrap the tape on an angle around the pipe with approximately 1/4 to 1/8 tape width overlap. Where manufacturer coated piping is used, all welded or threaded below ground joints must be coated and taped.

Figure 1. Coating and Wrapping a Threaded Piping Section

slide6

Methods Used to Protect Buried Tanks

Insulating Fittings – Insulating fittings are used when buried metallic distribution lines (especially copper tubing) are connected to underground tanks to isolate various parts of the pipeline system and for quality control in cathodic protection systems.

Figure 2. Insulating

Dielectric Union

slide7

Methods Used to Protect Buried Tanks

  • Sacrificial Anodes – Sacrificial anodes are used where
  • Current requirements are low
  • Metal structures to be protected are usually well-coated
  • Localized protection is required, and
  • Relatively low soils having low electrical resistance exist.
slide8

Methods Used to Protect Buried Tanks

Figure 3. Sacrificial Anode Installation

slide9

Installing Anodes and Testing Cathodic Protection

In almost all areas, corrosion of underground tanks is a serious problem. Tank failure can occur within months if the tank is connected to a copper distribution line. To reduce this problem, sacrificial anodes are installed in the ground near the tank or piping system.

  • The anodes are connected by a lead wire to a separate tank electrode installed on the tank by the tank manufacturer, a service technician at the bulk plant, or by the tank installer.
  • The final connection of the two lead wires is made at the customer installation location.
  • The practice of connecting the two lead wires near the inside top of the tank dome makes it easier to test the anode output on a periodic basis. This test ensures the tank is protected, and makes installation of additional sacrificial anode(s) possible without having to excavate and expose the tank.
slide10

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

  • For the thermit weld process to be effective, the attachment surface must be cleaned to bright metal.
  • Thermit, or “cadwelds” must not be made directly on the heads or shell of the tank. Rather, cad welds are done on a flat surface directly attached to the tank by the tank manufacturer.

NOTE:

Thermit weld cartridges should be of quality equal to or better than Cadweld CA15. CAUTION:Always wear gloves and goggles when igniting powder.

slide11

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

Figure 5. Cleaned Surface

Figure 4. Cleaning the Attachment Surface

slide12

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

Figure 6. Attaching the Copper Sleeve

Figure 7. Drying the Cadweld Mold

slide13

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

Figure 8.

Figure 9.

slide14

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

Figure 10.

Figure 11.

slide15

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

Figure 13.

Figure 14.

slide16

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

Figure 15.

Figure 16.

slide17

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

Figure 17. Cleaning

and Coating the Tank Electrode Weld

slide18

Attaching the Tank Electrode Lead Wire

Thermit or “Cad” Welding

Figure 18. Securing the Tank Electrode Lead on the Riser

slide19

Attaching the Tank Electrode Lead Wire

Conductive Adhesive Process—Recent advances in chemical manufacturing have produced electrically conductive adhesives that can be used to attach electrode leads directly to underground tanks and piping without subjecting the metal to high temperatures. When using this method for attaching tank or pipe electrodes, it is very important to read and strictly follow manufacturer instructions to obtain a secure electrode bond to the metal.

slide20

Attaching the Tank Electrode Lead Wire

Conductive Adhesive Process

Figure 19.

Figure 20.

slide21

Attaching the Tank Electrode Lead Wire

Conductive Adhesive Process

Figure 21.

Figure 22.

slide22

Attaching the Tank Electrode Lead Wire

Conductive Adhesive Process

Figure 23.

Figure 24.

slide23

Attaching the Tank Electrode Lead Wire

Conductive Adhesive Process

Figure 25.

Figure 26.

slide24

Attaching the Tank Electrode Lead Wire

Conductive Adhesive Process

Figure 27.

Figure 28.

slide25

Attaching the Tank Electrode Lead Wire

Conductive Adhesive Process

Figure 29.

Figure 30.

slide26

Attaching the Tank Electrode Lead Wire

Conductive Adhesive Process

Figure 31. Routing Lead

Wire into Tank Dome

slide27

Attaching the Tank Electrode Lead Wire

Tank Manufacturer Installed Electrodes

New underground tanks typically have manufacturer-attached tank electrodes that can be electrically connected to the anode lead. The lead wire and electrode weld must be inspected for proper insulation coverage and coating. The lead wire should be straightened and extended toward the top of the tank dome where its terminating end can be stripped of insulation and electrically connected to the anode lead wire.

Figure 32. Tank Manufacturer-Installed Electrode

slide28

Installing Underground Tank Anodes

Factors Important to the Installation of Underground Tank Anodes

  • The anode performs best when placed in the ground at the bottom of tank depth.
  • The anode should be placed at least two feet from the tank.
  • The anode may be positioned either horizontally in a ditch, or vertically in an augured hole.
  • After placing the anode unit in position, the surrounding soil should be moistened with water to start immediate action.
  • The anode's connector lead wire should be inspected for damage and repaired prior to connection to the tank electrode lead wire.
  • The tank electrode connection and wire must be coated after welding.
slide29

Attaching Anode Lead Wires to Pipe

  • Anode lead wires can be connected to buried metallic piping by
    • Cad Welding
    • Conductive adhesive method

Figure 33. Cad Weld Process on Steel Pipe

slide30

Preparing the Hole for Burying the Anode

The absence of a proper backfill can result in irregular consumption of the anode, thus providing erratic current output per pound of anode consumed.

Figure 34. Digging Hole for Anode Burial

slide31

Preparing the Hole for Burying the Anode

Some anodes are shipped in a paper and plastic wrapping filled with gypsum. The wrapping must be removed, while placing as much gypsum as possible in the bottom of the hole and surrounding the anode.

Figure 35. Remove the Anode

Wrapping, Placing the Backfill

Material in the Hole

Figure 36. Placing the Anode Bag in the Burial Hole

slide32

Repairing Underground Tank Coatings

Before setting the underground tank in the excavated hole, it should be thoroughly inspected for any damage, or abrasions to the protective coating material. After the tank is placed in the excavated hole, a final touch up to any area damaged during the installation should be done, paying special attention to the lifting lugs or any place where the lifting sling made contact.

Figure 38. Repairing Tank Coating Before Installation

Figure 39. Touching-Up Coating After Tank Placement

slide33

Connecting Lead Wires

Figure 41. Twist Bare Ends and Install Electrical Twist Lock

Figure 40. Strip the Lead Wire Ends

Figure 42. Sealing &

Securing Lead Wires

& Connector

slide34

Testing Cathodic Protection Systems

Pipe-to-Soil Potential ReadingsThere are various criteria used to determine the effectiveness of a cathodic protection system. The test criteria typically used is a minimum -0.85 voltage measured between the tank and ground through a reference electrode, typically a copper-copper sulfate half cell.

Figure 43. Making a Tank-to-Soil Voltage Reading on a Buried Tank

slide35

Time to See If You Got the Key Points of This Module…

  • Complete the Review on page 21.
  • See if you are ready for the Certification Exam by checking off the performance criteria on page 22.