Novel electrical resistance method to measure underdeposit corrosion and its inhibition in pipeline steels

In this work, the evaluation of under deposit corrosion (UDC) behaviour of X65 pipeline steel and its inhibition in oxygen corrosion conditions were studied. In the fundamental experimental study, a three-electrode electrochemical system was used to measure the corrosion rates and polarisation curves by linear polarisation resistance and potentiodynamic polarisation methods. The galvanic effect caused by the deposit was also studied by the zero resistance ammeter technique. An 8 in X65 pipeline internal corrosion monitoring system based on the ring pair electrical resistance sensor (RPERS) was established for further research of UDC. The underdeposit corrosion rate and its inhibitory effect in the pipeline were also monitored by RPERS. Electrochemical test results showed that the corrosion inhibitor amino trimethylenephosphonic acid (ATMP) would result an accelerate corrosion for UDC. A nearly 1.7 times increase was found on the galvanic current when ATMP was introduced into the solution. The inhibitor imidazoline had a good performance on UDC for both corrosion inhibiting and the reduction of the galvanic current. Through the monitoring results of RPERS, the UDC status in the pipeline and the effect of the inhibitors were studied. The monitoring results have a consistency with the fundamental experiment.