Induced Alternating Current Used for Cathodic Protection of a Coated Pipe Line★

CORROSION ◽  
1956 ◽  
Vol 12 (1) ◽  
pp. 17-19 ◽  
Author(s):  
S. J. BELLASSAI
Keyword(s):  
Salt Marsh ◽  
Cathodic Protection ◽  
Alternating Current ◽  
Selenium Rectifier ◽  
Leak Location ◽  
The Earth ◽  
High Line ◽  
Pipe Line ◽  
Graphite Rods ◽  
Circuit Resistance

Abstract After making repairs on a leak on a coated line through a salt marsh and paralleling a high voltage high line, it was learned that although considerable gradients existed in the earth adjacent to the high line there was no correlation in the measured quantities. It had been considered that natural rectification of the induced AC voltage was occurring. After tests with coupons buried near the pipe line showed the pipeline was predominantly positive to earth at the leak location, a test ground bed was constructed to examine the feasibility of rectifying the induced alternating current. Measurement of the rectified voltage between the pipeline and the test ground bed through a 25-ampere, 18-volt selenium rectifier was 5 volts DC available for cathodic protection. A 5-ampere, 15-volt selenium stack, ten 3-inch x 60-inch graphite rods and 500 feet of 1/0 copper cable was calculated to provide circuit resistance of the required value to protect the line cathodically.

New Cathodic Protection Criteria Based on Direct and Alternating Current Densities Measured Using Coupons and Their Application to Modern Steel Pipelines

CORROSION ◽  
2004 ◽  
Vol 60 (3) ◽  
pp. 304-312 ◽  
Author(s):  
Y. Hosokawa ◽  
F. Kajiyama ◽  
Y. Nakamura
Keyword(s):  
Cathodic Protection ◽  
Field Tests ◽  
Alternating Current ◽  
Pipe Material ◽  
Review Of The Literature ◽  
Density Measurements ◽  
Corrosion Risk ◽  
Ac Current ◽  
Current Densities ◽  
Dc Current

Abstract The risks of alternating current (AC) corrosion, overprotection, and stray direct current (DC) corrosion are increasing on cathodically protected buried steel pipelines due to the recent changes in factors such as burial conditions, the characteristics of coatings, and pipe material. In the present study, field tests as well as a review of the literature on these risks were conducted. As a result, it has been revealed that there is a certain limitation to assess these risks with respect to conventional cathodic protection (CP) criteria based on pipe-to-soil potential. Therefore, new CP criteria for the elimination of these risks have been developed based on DC and AC current density measurements on coupons. The effectiveness of the new CP criteria was evaluated through the design of CP systems on newly constructed pipelines subject to the risks of AC corrosion, overprotection, and stray DC corrosion. Using these new CP criteria, the design and installation of CP systems as well as the elimination of these risks were completed successfully. The risks of overprotection as well as stray DC corrosion were eliminated by providing an appropriate level of DC current from CP rectifiers. The elimination of the AC corrosion risk was accomplished using distributed magnesium anodes and solid-state DC decoupling devices. Finally, the new CP criteria were proven to be effective in eliminating the risks of AC corrosion, overprotection, and stray DC corrosion on buried steel pipelines.

The Low Potential Zinc Anode In Theory and Application

CORROSION ◽  
1961 ◽  
Vol 17 (11) ◽  
pp. 550t-556t ◽  
Author(s):  
J. R. WELLINGTON
Keyword(s):  
Cathodic Protection ◽  
Sea Water ◽  
Self Regulation ◽  
Anode Current ◽  
Cathode Polarization ◽  
Current Output ◽  
Zinc Anode ◽  
A Value ◽  
Protection Systems ◽  
Circuit Resistance

Abstract After a brief discussion of the principles of cathodic protection and the basic requirements of a galvanic anode, anode requirements are examined specifically in terms of the cathodic protection of iron or steel in an electrolyte of uniform characteristics. For sea water it is shown that it is desirable to limit the cathode polarization to a value less anodic than −1.1 v (vs Ag/AgCl). The advantages of a low potential anode for the cathodic protection of iron under these conditions are discussed in detail in terms of circuit resistance, self-regulation, and cunrent distribution on the cathode. Other desirable anode characteristics such as current efficiency, current capacity per unit volume, and the effect of anode shape on anode current output are examined mathematically. The practical advantages and implications of the above considerations are described. It is suggested that where cathode polarization controls current distribution on the cathode and regulates anode current output, a new concept can be advanced for the design of cathodic protection systems utilizing low potential zinc anodes. 5.2.2

Corrosion of Pipeline Steel in the Presence of Alternating Current and the New CP Recommendation

2010 ◽  
Author(s):  
A. Q. Fu ◽  
Y. F. Cheng
Keyword(s):  
Corrosion Rate ◽  
Current Density ◽  
Cathodic Protection ◽  
Pitting Corrosion ◽  
Pipeline Steel ◽  
Alternating Current ◽  
National Association ◽  
Ac Current ◽  
Ac Interference ◽  
Full Protection

The alternating current (AC)-induced corrosion of a cathodically protected X65 pipeline steel was studied in a high pH, concentrated carbonate/bicarbonate solution. Results demonstrated that the corrosion rate of the steel increases with the AC current density, and AC interference could increase the pitting corrosion of the steel. In the absence of AC interference or at a low AC current density, i.e., 20 A/m2, a cathodic protection (CP) potential of −950 mV(Cu/CuSO4 electrode, CSE), which is 100 mV more cathodic than −850 mV(CSE) recommended by National Association of Corrosion Engineers (NACE), provides a full protection over the steel. When the AC current density is higher than 20 A/m2, the NACE-recommended CP is incapable of protecting the pipeline from corrosion. A new CP standard is thus developed for recommendation to industry to avoid AC corrosion of pipelines.

Continuous Recording of Pipe-to-Soil Potential vs Distance

CORROSION ◽  
1961 ◽  
Vol 17 (9) ◽  
pp. 446t-448t
Author(s):  
ROBERT L. DAVIS
Keyword(s):  
Cathodic Protection ◽  
Hot Spots ◽  
Continuous Recording ◽  
Recording Device ◽  
Electrical Field ◽  
Metallic Structures ◽  
The Earth ◽  
Efficiency And Effectiveness ◽  
Further Development

Abstract Equipment and a method useful in making a continuous recording of pipe-to-soii and certain other potentials significant in cathodic protection of underground metallic structures are described. The device consists of a wheel electrode, mechanically and electrically connected to a recording device which plots distances and potentials continuously as it is rolled along the earth's surface over a pipeline, or over an electrical field in the earth. The method permits locating “hot spots” on lines with considerable accuracy, usually within a few feet. This radically improves the efficiency and effectiveness of protection at these points. Further development of the device to record the direction of currents is contemplated using modified equipment. 4.5.3, 7.7

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