Buried steel pipeline corrosion factor analysis

Buried pipelines in the working environment, mainly with soil erosion corrosion, bacteria, corrosion and stray current corrosion. Soil is a solid, liquid and gas -phase capillary porous gelatinous body, the soil voids is filled with air and water, the water contains a certain amount of salt, so that the soil has ionic conductivity, soil physical and chemical properties of heterogeneous and metal electrochemical inhomogeneity, constitute electrochemical corrosion of buried pipeline conditions, which will produce soil erosion. In some soil bacteria oxygen ( SRB ) participated in the etching process, the role of bacteria is to participate in the electrode reaction, the soluble iron sulfate to hydrogen sulfide, thus producing bacterial corrosion. Stray current is flowing in the ground outside the protection system design corrosive to metal pipes damaging effects of current. Stray current corrosion including DC and AC stray current corrosion stray current corrosion. DC stray current corrosion principles and electrolytic corrosion similar to AC stray current corrosion is a pipe near high voltage power lines generated by the second induction AC superimposed on the pipeline corrosion corrosion resulting electrochemical cell , the corrosion was smaller, but concentrated corrosion resistance.

Corrosion protection control pipe corrosion damage is a key factor. Currently, the pipeline corrosion protection using a double measures, namely anti-corrosion coating and cathodic protection ( impressed current or sacrificial anode exhaust stream ). Anti-corrosion coating can withstand corrosive environment of the scene to ensure that the pipe firmly bonded, does not appear possible cause cathodic protection cathodic stripping and dead. In the event of partial peeling, you must adjust the impressed current cathodic protection system operating parameters, in order to effectively control the dead corrosion achieve the protective effect. Tube material and manufacturing factors are internal pipeline corrosion, especially steel chemical composition and crystalline structure, high content of non-metallic components ( such as S and P) prone to corrosion, C and Si could easily lead to brittle cracking. Microcrystalline fineness of low-grade, cracks along the grain expansion , prone to cracking. In the manufacturing process, the surface defects ( such as scratches , pits, micro-crack , etc. ), also cause pipe corrosion cracking. Pipeline operation is running, delivery pressure and pressure fluctuations are an important factor in stress corrosion cracking. Excessive pressure to the wall using excessive stress corrosion crack easy to make, easy to make pressure cycle fluctuations crack.