Control and Maintenance of Cathodic Protection

Off potentials cannot be used to control cathodic protection. Such a measurement is only correct if the dc decoupling devices are isolated from the grounding 

To evaluate the cathodic protection—with the exception of very high-resistance soils—from experience, an average value of the on potential of t/cu.cuso4 = -1 -5 V is to be used. With this value, no danger from stray currents should be experienced [6]. 

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Likelihood factors are associated with the system attributes associated with the individual causes of failure. Likelihood factors include such considerations as pipe coating, degree of cathodic protection, soil conditions, pipe age, and maintenance history for corrosion control and depth of burial surrounding land use and activities, one-call system effectiveness, effectiveness of system marker signs, and other factors for third-party damage potential, to cite some examples. 

The advantages of SACP are that it does not need mains power, a T/ R, instrumentation or much maintenance. Its shortcomings are the lack of control of the system, consumption of the anode and the need to keep resistance low. If present trials and research show the system to be feasible, this could encourage more engineers to try out this comparatively simple form of cathodic protection. 

Cathodic protection is used widely for the protection of submerged steel in waterfront structures. It also can provide considerable benefit in the intertidal zone and can even reduce the usually high corrosion rate experienced at the boundary between the intertidal zone and the splash and spray zone. Cathodic protection also is used to prevent corrosion of the soil side of steel in marine structures such as sheet steel bulkheads. Cathodic protection also is effective in the control of the corrosion of reinforcing steel in concrete in all exposure zones in waterfiont structures. Particularly for impressed current systems, it is important to select materials for the cathodic protection system components such as rectifiers and junction boxes with consideration of the environment to which they will be exposed. When considering cathodic protection, periodic inspection and maintenance is required for proper system operation. The costs for inspection and maintenance must be considered in the overall cost of cathodic protection. While there are no specific standards for cathodic protection of piers and docks, information in NACE RP0176 (Corrosion Control of Fixed Offshore Platforms Associated with Petroleum Production) and NACE RP-0187 (Design Considerations for Corrosion Control of Reinforcing Steel in Concrete) contain information that is applicable to marine piers and docks. 

Control of External Corrosion on Underground or Submerged Metallic Piping Systems Design, Installation, Operation, and Maintenance of Impressed Current Deep Groundbeds Corrosion Control of Electric Underground Residential Distribution Systems Design, Installation, Operation, and Maintenance of Internal Cathodic Protection Systems in Oil... 

Although the imderlying principle of cathodic protection is a relatively simple one, considerable attention needs to be directed at details such as soimd electrical connections, reliable reference electrodes, durable control cabinets, possible short circuits between the anodes and rebar, and maintenance schedules for the CP hardware. 

Corrosion. Anticorrosion measures have become standard ia pipeline desiga, coastmctioa, and maintenance ia the oil and gas iadustries the principal measures are appHcation of corrosion-preventive coatings and cathodic protection for exterior protection and chemical additives for iaterior protectioa. Pipe for pipelines may be bought with a variety of coatiags, such as tar, fiber glass, felt and heavy paper, epoxy, polyethylene, etc, either pre-apphed or coated and wrapped on the job with special machines as the pipe is lowered iato the treach. An electric detector is used to determine if a coatiag gap (hoHday) exists bare spots are coated before the pipe is laid (see Corrosion and corrosion control). 

Corrosion damage is a major factor in ship maintenance and availability. Coatings combined with the impressed current cathodic protection (ICCP) system are the most common means for shipboard corrosion control. They interact with each other to protect the shipboard. Coatings provide primary corrosion protection by isolating the hull metal from seawater, while ICCP systems protect the hull by applying an external source of current to the ship where the paint is damaged or degraded. 

Control Costs. These include costs for maintenance and repair and for corrosion control (cathodic protection, water treatment, etc.). They are borne by all sectors of the economy. 

Inputs. These include the costs of coatings and plating for corrosion control, corrosion inhibitors, maintenance and repair, corrosion-resistant metals, and cathodic protection. 

Basic Supervisory Control and Data Acquisition Systems (SCADA) Pressure testing for steel and plastic pipelines Hot tapping and stopping Characteristics and properties of natural gas Excavation safety Compressor operation Pipeline purging Valve maintenance Cathodic protection... 

The capacity of the tran.sformer/rectifier and of the anode can be estimated from Figure 6,18 taken from Bennett and Turk (1994), One possible use of this chart, if it can be sufficiently validated, may be to eliminate the need for probes and control systems for cathodic protection. Once the highest chloride level at rebar depth is found during the condition survey, then the current is set at the appropriate level and left. The only maintenance need would be to ensure that the system is working and the current is being applied fairly uniformly to the structure. 

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