S.r. Allahkaram, R. Shamani,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: Due to the expansion of high voltage Alternating Current (AC) power transmission lines and cathodically
protected buried pipelines, it is becoming more and more difficult to construct them with enough safe distances
between them. Thus, the pipelines are frequently exposed to induced AC interferences, which result in perturbation of
Cathodic Protection (CP) due to AC corrosion. To study the above criterion, an experimental set up was used with
coupons exposed to simulated soil solutions, while under both CP and AC induced condition for which an AC+DC
power supply was utilized. The experiments were carried out in several simulated soil solutions corresponding to
several soil samples collected from various regions along a buried pipeline with overhead parallel high voltage power
transmission line. The results indicated that AC corrosion depends strongly on the composition of the soil.
S.r. Allahkaram, R. Shamani,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract: The risks of alternating current (AC) corrosion and overprotection increasingly demand new criteria for
cathodically protected pipelines. To assess the risk of AC corrosion, new cathodic protection (CP) criteria have been
proposed based on DC/AC current densities measurements using coupons. The monitoring system designed for this
project was based on the instant-off method, with steel coupons simulating coating defects on a buried pipeline. The
problems associated with the instantaneous off-potential measurements have been attributed to a non-sufficient time
resolution. In present study, it has been possible to determine the de-polarisation of steel coupon within a few
milliseconds after disconnecting the coupon from the DC/AC power source, by increasing data acquisition rate. For
this, a monitoring system was developed in order to measure the IR-free potential together with the DC/AC current
densities. The monitoring system was utilized for both laboratory experiments and site survey to study the mechanism
and the condition of AC corrosion, its mitigation and more importantly to define new CP criteria.
