In order to ensure the safe operation of submarine pipelines during the designed life, the pipeline system shall fully prevent internal and external corrosion caused by the transport medium and seawater.
Engineering practice proves that in actual seawater environments, the outer coating can provide effective corrosion protection. The outer coatings for submarine pipelines include coal tar enamel, asphalt enamel, epoxy resin, polyethylene resin, polybutadiene rubber, and the like.
As a supplement and reinforcement to the outer coating, cathodic protection provides adequate protection during the design life of the submarine pipeline system. Cathoc protection systems for subsea pipelines are usually based on sacrificial anodes.
The material of the sacrificial anode may be an alloy of aluminum or zinc. The weight and number of anodes are related to the resistivity of the surrounding soil, the current density requirements, the criteria for coating failure, and the design life of the pipeline. In the design, the weight of the anode, the distribution distance, the length and thickness of each pole block should be calculated. On coated subsea pipelines, the distance between the two anodes is generally not more than 150m. The shape of the anode includes a strip shape, a plate shape, and a semi-ring shape.
The anode shall be installed on the pipeline in such a way that it will not be mechanically damaged during the loading and unloading of the pipe and during construction. The diameter of the anode block shall be smaller than the diameter of the weighting layer and shall be firmly fixed on the pipe. In order to ensure a reliable mechanical connection between the anode and the tube and the correct position, the two half rings can be welded together
(3)Control of internal corrosion
Internal corrosion control should be carried out for pipeline systems carrying corrosive hydrocarbons. For submarine pipelines, the internal corrosion control methods include the use of corrosion inhibitors, plus corrosion allowances, internal coatings, and corrosion-resistant pipes or linings to keep the transport medium dry.
The internal anticorrosion scheme is determined based on the properties of the conveyed medium, including the ratio of oil, gas, and water; salt content, bacterial content, and water pH; the content of corrosive gases; the solid content and its flow characteristics; temperature And stress
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Post time: Apr-10-2020