20 MARCH 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 3
MATERIAL MATTERS
rupted, you locate each individual pipe
and take a reading on each pipe, standing
over it."
He adds that in many cases, it is ben-
ef icial to get other operators in the area to
allow synchronized current interruption
on their CP systems, so all available cur-
rent sources in the area are controlled for
better CIS results. "In addition, if one
moves laterally away from the target line
to take reads, there can be no other struc-
tures in the way," Chapman says. "That's
part of the standard."
In another f ield case, a company oper-
ating a 27-mi (43.5-km) pipeline segment
that connects a gathering terminal to a
ref inery near the U.S. Gulf Coast had doc-
umentation showing two CP systems near
both ends of the line giving a total output
of 16 A. According to Chapman's team,
another CIS contractor had deemed that
to be suff icient.
When comparing that data to prior
f indings, however, Chapman's team found
that the same system provided 25 A of
output before a hurricane struck the
region several years ago. The pipeline was
installed in 1982 with girth welds every
40 ft [12.2 m] and shrink sleeves as their
coating. Data showed 15 to 20 external
corrosion problems had already been
documented where there had been an
excavation, recoating, or a sleeve put on a
pipe, Chapman says.
"That shows you the amount of CP put
on this pipe for a long time has been sub-
standard," Chapman says. "And that's
when it had 25 [A] on it, not 16."
"A ll those calculations and the age of
the pipe allowed me to say that it proba-
bly needs 50 [A] or even more to be truly
protected," Chapman recalls. "A ll it took
was a look at the historical data, the big
pipe diameter, and the long pipe length."
The SP0207 standard specif ies that previ-
A pipeline without a coating or effective CP
may show major variations in voltage
measurements with distance surveyed, due
to its proximity to other pipelines and
changes in soil characteristics. Photo by
Charlie Hernandez, Chapman Engineering.
Continued f rom page 19