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Cathodic protection of pipe lines
July,1939.1 NATIONAL BUREAU OF STANDARDSNOTES.
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a locality for the building where the noise level is not excessively high. Also, when it is desirable that some rooms should be quieter than others, they should be placed where there will be the least disturbance from normal noises which occur in the building. The report summarizes the data on the construction of many of the panels which have been tested at the Bureau, and their corresponding sound insulating properties. Copies of BMSI-/ are obtainable from the Superintendent of Documents, Government Printing Office, Washington, D. C., at IO cents each. CATHODICPROTECTIONOF PIPE LINES. The use of cathodic protection has rapidly increased since the first installation on gas transmission lines in 1930, until now practically all of the large companies are using this method to prevent the corrosion of parts of their pipe line systems. Cathodic protection is usually installed on lines that were properly coated before they were laid. By applying current cathodically the potential of the entire pipe line is lowered with respect to a reference half-cell in the surrounding soil so that current flows toward the pipe through any imperfections in the coating. However, by careful design and proper location of anodes from which the drainage current is discharged into the soil, it has been found to be economical in certain cases to apply cathodic protection to bare lines such as gas pipe lines of large diameter. On bare oil lines, which are of smaller diameter, reconditioning operations still seem to be preferable to cathodic protection if the occurrence of leaks should become excessive. At the meeting of the Petroleum Industry Electrical Association in Houston, Texas, the afternoon of May 4 was devoted to a paper entitled “Applications of Electrochemistry to Cathodic Protection ” which was presented by Scott Ewing, Research Associate of the American Gas Association at the Bureau. In this paper some electrochemical principles were discussed which will be useful to the cathodic protection engineer by helping him make more accurate voltage measurements and by giving him a better understanding of the
94
NATIONAL BUREAU OF STANDARDSNOTES.
[J. F. I.
corrosion process. The design of copper-copper sulfate and cadmium-cadmium sulfate half-cells ha& been improved to correct some of the faults of the half-cells previously used. (See Technical News Bulletins 264 and 265, March and April, 1939.) A brief .description of these improved half-cells was given, together with temperature correction curves. With these half-cells the potential difference between two points in the soil can be measured with an error not greater than 2 mv. A consideration of the potentials and currents in a corroding pipe line indicates that in some cases it should be possible to apply cathodic protection to bare pipe lines of small diameter. The protective current should be drained from the pipe line in places where the reference half-cell has a large positive potential with respect to the pipe line. In such places the pipe is usually found to be discharging current into the soil. By locating anodes so as to take advantage of the galvanic currents in the pipe line, a much greater length of line can be protected with one anode. The potential of the pipe with respect to a reference half-cell is not appreciably changed except in the originally anodic area near the anode. This is probably the only part of the line that really needs protection. The feasibility of the method depends upon the distribution and stability of the originally anodic areas along the pipe line. Whether it is economical or not will depend upon the relative costs of cathodic protection and probable future reconditioning. ALLOYS FOR ELECTRICALHEATING ELEMENTS. The manufacturers of electric heating devices, from toasters to furnaces, as well as the users of these devices, have always been vitally interested in the life and maximum operating temperature of the heating unit. Various types of tests, such as the “Accelerated Life Test for Metallic materials for Electrical Heating” B76-38 of the American Society for Testing Materials, have been devised with the view of predicting the life expectancy of a heating element The operating under specified conditions of operation. temperature of the material probably has more effect upon
93
a locality for the building where the noise level is not excessively high. Also, when it is desirable that some rooms should be quieter than others, they should be placed where there will be the least disturbance from normal noises which occur in the building. The report summarizes the data on the construction of many of the panels which have been tested at the Bureau, and their corresponding sound insulating properties. Copies of BMSI-/ are obtainable from the Superintendent of Documents, Government Printing Office, Washington, D. C., at IO cents each. CATHODICPROTECTIONOF PIPE LINES. The use of cathodic protection has rapidly increased since the first installation on gas transmission lines in 1930, until now practically all of the large companies are using this method to prevent the corrosion of parts of their pipe line systems. Cathodic protection is usually installed on lines that were properly coated before they were laid. By applying current cathodically the potential of the entire pipe line is lowered with respect to a reference half-cell in the surrounding soil so that current flows toward the pipe through any imperfections in the coating. However, by careful design and proper location of anodes from which the drainage current is discharged into the soil, it has been found to be economical in certain cases to apply cathodic protection to bare lines such as gas pipe lines of large diameter. On bare oil lines, which are of smaller diameter, reconditioning operations still seem to be preferable to cathodic protection if the occurrence of leaks should become excessive. At the meeting of the Petroleum Industry Electrical Association in Houston, Texas, the afternoon of May 4 was devoted to a paper entitled “Applications of Electrochemistry to Cathodic Protection ” which was presented by Scott Ewing, Research Associate of the American Gas Association at the Bureau. In this paper some electrochemical principles were discussed which will be useful to the cathodic protection engineer by helping him make more accurate voltage measurements and by giving him a better understanding of the
94
NATIONAL BUREAU OF STANDARDSNOTES.
[J. F. I.
corrosion process. The design of copper-copper sulfate and cadmium-cadmium sulfate half-cells ha& been improved to correct some of the faults of the half-cells previously used. (See Technical News Bulletins 264 and 265, March and April, 1939.) A brief .description of these improved half-cells was given, together with temperature correction curves. With these half-cells the potential difference between two points in the soil can be measured with an error not greater than 2 mv. A consideration of the potentials and currents in a corroding pipe line indicates that in some cases it should be possible to apply cathodic protection to bare pipe lines of small diameter. The protective current should be drained from the pipe line in places where the reference half-cell has a large positive potential with respect to the pipe line. In such places the pipe is usually found to be discharging current into the soil. By locating anodes so as to take advantage of the galvanic currents in the pipe line, a much greater length of line can be protected with one anode. The potential of the pipe with respect to a reference half-cell is not appreciably changed except in the originally anodic area near the anode. This is probably the only part of the line that really needs protection. The feasibility of the method depends upon the distribution and stability of the originally anodic areas along the pipe line. Whether it is economical or not will depend upon the relative costs of cathodic protection and probable future reconditioning. ALLOYS FOR ELECTRICALHEATING ELEMENTS. The manufacturers of electric heating devices, from toasters to furnaces, as well as the users of these devices, have always been vitally interested in the life and maximum operating temperature of the heating unit. Various types of tests, such as the “Accelerated Life Test for Metallic materials for Electrical Heating” B76-38 of the American Society for Testing Materials, have been devised with the view of predicting the life expectancy of a heating element The operating under specified conditions of operation. temperature of the material probably has more effect upon