4.2.10

1. 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

2. 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.

3. 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.)

4. 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.

5. 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

6. 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

7. 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.

8. Methods Used to Protect Buried Tanks Figure 3. Sacrificial Anode Installation

9. 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.

10. 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.

11. Attaching the Tank Electrode Lead Wire Thermit or “Cad” Welding Figure 5. Cleaned Surface Figure 4. Cleaning the Attachment Surface

12. Attaching the Tank Electrode Lead Wire Thermit or “Cad” Welding Figure 6. Attaching the Copper Sleeve Figure 7. Drying the Cadweld Mold

13. Attaching the Tank Electrode Lead Wire Thermit or “Cad” Welding Figure 8. Figure 9.

14. Attaching the Tank Electrode Lead Wire Thermit or “Cad” Welding Figure 10. Figure 11.

15. Attaching the Tank Electrode Lead Wire Thermit or “Cad” Welding Figure 13. Figure 14.

16. Attaching the Tank Electrode Lead Wire Thermit or “Cad” Welding Figure 15. Figure 16.

17. Attaching the Tank Electrode Lead Wire Thermit or “Cad” Welding Figure 17. Cleaning and Coating the Tank Electrode Weld

18. Attaching the Tank Electrode Lead Wire Thermit or “Cad” Welding Figure 18. Securing the Tank Electrode Lead on the Riser

19. 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.

20. Attaching the Tank Electrode Lead Wire Conductive Adhesive Process Figure 19. Figure 20.

21. Attaching the Tank Electrode Lead Wire Conductive Adhesive Process Figure 21. Figure 22.

22. Attaching the Tank Electrode Lead Wire Conductive Adhesive Process Figure 23. Figure 24.

23. Attaching the Tank Electrode Lead Wire Conductive Adhesive Process Figure 25. Figure 26.

24. Attaching the Tank Electrode Lead Wire Conductive Adhesive Process Figure 27. Figure 28.

25. Attaching the Tank Electrode Lead Wire Conductive Adhesive Process Figure 29. Figure 30.

26. Attaching the Tank Electrode Lead Wire Conductive Adhesive Process Figure 31. Routing Lead Wire into Tank Dome

27. 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

28. 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.

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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.