Condition assessment of steel pipelines
In its over 100-year history, the steel pipe has developed into a reliable steel line pipe, for example, in the utilities industry. With its thick film coating systems, the steel line pipe as manufactured for many decades now, is a composite pipe which differs from bare steel pipe in that design regulations specify no corrosion allowance for the wall thickness. As long as the plastic materials used as thick-film systems maintain their barrier properties, corrosion processes must only be considered in the event of insufficient care in pipe-laying or external influences.
Since the 1950s, cathodic corrosion protection has been used especially for these pipelines. Meantime, it not only serves to protect the base material in the event of damage to the pipe coating, but also enables the condition of a pipeline to be assessed based on its special measuring methods. Thus, the need for action regarding repair measures can be derived from the measurement results. This means the planning of measures does not start from the failure probability of damage statistics, but from concrete limit states of a pipeline or a pipeline section. Conceptually, damage or failure of a cathodically protected pipeline is not envisaged.
Through continuous monitoring of the operating data of cathodic corrosion protection, even external influences can be detected today. These possibilities were investigated in a project group of the DVGW. The project results form the basis for defining the requirements for monitoring systems in DVGW Code of Practice GW 31. The Code of Practice was published in November 2020.