Predicting service life of steel tubes in building and industrial services.

There is a real need to be able to predict the service life of pipework systems taking account the relevant service conditions. The requirement is to translate corrosion control and corrosion behaviour of small-scale coupons representing small parts of pipes to the behaviour of larger pipework systems (for industrial relevance). The research considered a range of factors influencing corrosion and methods currently used for assessing and determining corrosion rates of pipework systems. Linear Polarization Resistance (LPR) was used to compare results of static and dynamic measurements on carbon steel tubes. The effect of dissolved oxygen, flowrate, surface condition, water chemistry and weld were investigated. Other factors were considered for example; material composition, water (source, composition, hardness), temperature and time. In order to provide recommendations to accurately predict long service life of metal pipework systems from short duration measurements, a range of relevant service conditions were set up with tap water (from two sources) conveyed in open and closed systems. Data was assembled from a range of measurement methods and systems in small scale laboratory tests and flow loops to represent pipework systems. The data generated demonstrated correlation and highlighted that dissolved oxygen and flow rate were the main factors influencing corrosion measurement across length scales in static and dynamic environments. A case study was undertaken to consider issues around monitoring a small pipework system in reality. Corrosion is a dynamic activity and careful attention to a range of influencing factors experienced by a pipe system before and during service and it is important to gather as much relevant information as possible. The use of LPR probes, the probe cleanliness and maintenance, care with handling coupons and a combination of water analysis and LPR measurements are recommended to improve the prediction of service life.