Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Appendix C Definitions The required criteria for corrosion control call for some terms that may not be familiar. Although these items are covered in more detail within the body of the report, brief descriptions are provided below for clarity of the general corrosion control discussion. anode: The positive electrode or metallic surface location where direct current is discharged into a surrounding electrolyte and corrosion (oxidation with a loss of electrons) occurs in a corrosion cell. The opposite of a cathode. appurtenance or fitting: Items including but not limited to valves, bends, tees, glands, restrained joints and joint restraints, couplings, spool pieces, miscellaneous piping, tapping saddles, blow-off valves, or hydrants, including metallic glands. bell-and-spigot pipe joint: The spigot end of a pipe, which is the same diameter as the pipe barrel, fits into a bell that is larger than the spigot, and a gasket is then used to contain pressurized material. Additional mechanical restraints, such as bolts or collars, may also be used to keep the joint intact. Bell-and-spigot joints may be push-on, mechanical, or restrained joints. bonded dielectric coating: An electrical insulating coating that is physically attached to the pipe surface. cathode: The negative electrode or metallic surface location where direct current 155
156 Corrosion Prevention Standards for Ductile Iron Pipe is received or collected from a surrounding electrolyte and protection (reduction with a gain of electrons) occurs in a corrosion cell. The opposite of an anode. cathodic protection criteria: The National Association of Corrosion Engineers (NACE) criteria for cathodic protection levels in accordance with NACE Standard 169, âTG 169 Cathodic Protection of Pipelines in Seawater.â cathodic protection station: An impressed-current cathodic protection installation location usually consisting of a rectifier and ground bed. cathodic protection system: Two common cathodic protection methods are gal- vanic anodes and impressed-current cathodic protection systems. A galvanic anode system consists of galvanic anode material (usually magnesium or zinc) that natu- rally corrodes or sacrifices itself and does not require an outside power source. An impressed-current-type system employs an outside power source, usually a rectifier (that converts alternating current to direct current) and forces (impresses) cur- rent from a number of anodes (or ground bed) through the environment to the structure to be protected. corrosion monitoring system: A system of test stations, joint bonds, and insula- tors that provides an electrically continuous pipeline that is electrically insulated from other structures and provided with test stations at specified locations to allow monitoring of various testing methods, including pipeline potential, galvanic anode outputs, electrical continuity, electrical isolation, and cathodic protection testing. coupons: Use of two small bare pieces (coupons) of the base type of pipe and an on/off switch that allows one coupon (protected) to be connected into the cathodic protection system and one coupon (unprotected) to freely corrode with no pro- tection. The pair of coupons and on/off switch are used to allow various cathodic protection measurements (on, instant-off, and static [freely-corroding] potentials as well as current collection and direction measurements) to be used to ascertain protection levels provided to the structure. electrical isolation: The condition of being electrically isolated from other metallic structures (including, but not limited to, piping, reinforcement, and casings) and the environment as defined in NACE PR0286, âThe Electrical Isolation of Cathodi- cally Protected Pipelines.â electrically continuous pipeline: A pipeline that has a linear electrical resistance equal to or less than the sum of the resistance of the pipe plus the maximum
A pp e n d i x C 157 allowable bond resistance for each joint as specified or recommended by the pipe designer or pipe manufacturer. fastener: Items including but not limited to bolts, nuts, washers, tees, tie-rods, and restraining devices. ferrous metallic pipe: Any pipe or fitting made of steel or iron, or pipe containing steel or iron as a principal structural material (such as steel, ductile iron, and cast iron), except reinforced concrete pipe or stainless steel. holiday: A physical defect, damage, tear, or puncture in the loose polyethylene or a physical defect, disband, or damage in bonded dielectric coatings. joint bond: A method of making a pipeline electrically continuous by connecting insulated copper wire(s) or strap(s) across each side of the pipe joint or fitting. lead, lead wire, joint bond, pipe-connecting wire, cable: Insulated copper conduc- tor; the same as wire. loose bonded coating: A dielectric coating that is not bonded or physically attached to the pipe surface (polyethylene encasement, polywrap, wrap, encasement, etc.). plastic reference pipe: Plastic conduit or pipe placed in soil next to the structure to allow a portable reference electrode to be inserted for structure-to-reference electrode potential measurements. potential, structure-to-reference electrode potential (also structure-to-reference electrode voltage): Common method to determine corrosion protection levels by measuring the difference in voltage (potential) between the subject metallic struc- ture and the electrolyte in which it is buried or submerged, as measured to the standard specified reference electrode (usually a copper/copper sulfate reference electrode) placed in contact with the electrolyte. raceway: Conduit, sheath, plastic or metal pipe, or electrical metallic conduit (elec- trical metallic tubing) for casing of electrical or cathodic protection cables. resistance probe: Use of a probe with a known resistance to determine the amount of corrosion over a given period of time. As corrosion of the thin resistance probe occurs, the probe resistance increases. By measuring the resistance of the resistance probes over a period of time, the amount of corrosion activity that has occurred can be calculated in mils per year.
158 Corrosion Prevention Standards for Ductile Iron Pipe test station: Insulated lead wire connections to the structure, which are brought to a test station terminal board or box in order to allow an electrical connection to be made to the structure for above-grade corrosion and cathodic protection testing.
