Closed
Cycle Vapour Turbogenerator
A Reliable Cost-Effective Solution for Pipeline Rehabilitation
With its ability to operate
from within the most difficult conditions due to its flexibility and
multi-fuel capability, the Closed Cycle Vapour Turbogenerator (CCVT)
has become the optimum choice for power and system support for major
gas and oil pipeline projects, says Jean Gropper
Introduction
Rehabilitating pipeline-coating systems represents
a costly and timeconsuming process that too often requires removing
and replacing coatings in good condition along with the deteriorated
coating. In the pipeline’s early life, a carefully controlled increase
in installed cathodic protection grounded output may be the most cost-effective
method for minimising corrosion where coating deterioration is, or has,
occurred. Pipeline construction records, operational history, potential
surveys and electronic pigging surveys must be carefully analysed when
selecting a short/long-term pipeline repair, rehabilitation, or replacement.
In most cases, individual repairs must be completed at any cost on a
non-negotiable basis. The decision to rehabilitate or replace the line
or sections of the line can be made after a review of all data. The
first consideration in the decision should be to evaluate the effect
of additional cathodic protection either with existing cathodic protection
installations, or with new systems, which can be installed and operated
in remote locations. Existing pipeline supervisory control and data
acquisition (SCADA) systems can be extended to optimise cathodic protection
(CP), data acquisition and online analysis. New impressed-current cathodic
protection systems, in almost all cases, will be more cost effective
than repairing or replacing sections of an existing pipeline. Self-contained
remote-power cathodic protection power generators have been successfully
used for domestic and international pipeline corrosion control for over
30 years. However, the most flexible and reliable power generator system
is the Closed Cycle Vapour Turbogenerator (CCVT), based on user response
and operational case histories.
Pipeline Rehabilitation
Considerations
External pipe surfaces of buried systems are exposed
to many different corrosion environments along the same and pipeline
integrity is assured by the combined effect of coatings and cathodic
protection. All coatings have holidays that occur during the application
or handling processes. If no cathodic protection is provided for the
protection of the pipeline surface at holidays, penetration of the pipe
steel may occur as fast as uncoated steel. Pipeline steel surfaces can
be protected with cathodic protection and no coating, but the cost is
prohibitive and the effectiveness is limited. New or alternative performance
standards create special problems for pipeline operators and their technical
staff. Innovative methods are required:
l To determine cost-effective solutions for repair/rehabilitation
of existing pipelines
2 To recommend replacement when repair alternatives are not economical
3 To recommend an increase in cathodic protection impressed current
capability when appropriate
Evaluating Coating Conditions
In the last years, pipeline companies appear to
be changing their criterion for establishing adequate cathodic protection
on their pipelines. In the past, the standard criterion was -850 millivolts
for the pipeline contact versus a copper-copper sulfate reference electrode.
In an attempt to improve the seasonal variability of the potential readings
in different soil conditions and resistivities, several companies use
the accepted reading as measured with the cathodic protection current
momentarily interrupted. The “current off” potential measurement
reduces the “current on” potential by eliminating the effect
of IR drop, which is a function of applied current flowing through the
soil of varying resistivity.
cont....
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