API RP 1632:2010 pdf download
API RP 1632:2010 pdf download.Cathodic Protection of Underground Petroleum Storage Tanks and Piping Systems.
3.1 Description
3.1.1 Corrosion protection with sacrificial anodes may be used in preference to an impressed-current system where current requirements are low. Sacrificial anodes are usually constructed of zinc or magnesium metal, packaged in a low- resistivity backfill. Zinc anodes are best utilized in low- resistivity soils where their lower current output will result in longer anode life. Magnesium anodes, because of their higher driving potential (—1.6 volts compared to —1.1 volts for zinc), are frequently used in higher resistivity soils or soils with high concentrations of carbonates. bicarbonates. or phosphates.
3.1.2 Low driving voltages and low-current outputs (usually less than 0. 10 amperes per anode) generally limit sacrificial anodes to cathodic protection of well-coated struct tires. Sacrificial anode corrosion protection systems are particularly suited to new installations involving coated tanks and/or distribution piping.
3.2 Factory-Installed Anodes
3.2.1 Underground storage tanks are available from tank manufacturers with sacrificial anode cathodic protection systems already attached. Current requirements are minimized by factory application of long-lasting corrosion resistant coatings. Sacrificial anodes are attached at the plant. with anode weight and size determined by the tank surface area. Nonconductive bushings and flanges are provided with each tank to isolate the tank from any extra current demand resulting from electrical contact between the tank and associated metal piping. These bushings and flanges must be used to protect the tank and maintain the supplier’s warharm structure coatings or produce interferences with nearby buried structures.
h. Reliability of cathodic protection system components.
2.3.4.3 In some instances, on-site surveys may be required to obtain information necessary for specific designs. In other cases, designs may be sufficiently versatile to cover the wide range of conditions normally encountered.
2.3.5 INSTALLATiON
The installation of cathodic protection systems involves the use of wire conductors connecting anodes and structures, anodes and test stations, and anodes and rectifiers. The exact location of such wiring and anodes should be carefully identified on a plot plan of the facility, and a copy of this plan should be maintained by the owner.
L ANODE PROTECTION
ranty. These tanks may also be obtained with factory- installed test leads which facilitate field monitoting of anode current output and tank-to-soil potential.
Note: Steel product piping isolated from the tank by nonconduclive bushings and flanges will require its own cathodic protection system.
3.2.2 Factory-installed cathodic protection systems for new tanks are designed to satisfy requirements for most soil situations. The purchaser should compare conditions present at the proposed installation sites with the conditions tinder which long-term corrosion protection is provided by the factory-installed system.
3.2.3 Tanks with factory-installed cathodic protection systems must be handled carefully during transportation and installation to protect against coating damage or rupture of anode packages. Anode wires, test leads, tank coating. and tank isolation bushings should be inspected for obvious damage prior to final installation. As with any cathodic protection system. a regular postinstallation monitoring program is necessary to determine that corrosion protection is being maintained.
3.3 Field-Installed Anodes
3.3.1 Field-installed, sacrificial-anode cathodic protection systems may also be used to protect new or existing well- coated tanks and piping. A coal tar coating routinely applied to steel petroleum storage tanks should not be considered art adequate coating for cathodic protection purposes. Many of the corrosion resistant coatings used on cathodically protected petroleum pipelines (see NACE RP-Ol-69) may also be used as coatings for buried petroleum-storage tanks and dispensing piping.
