Page 90 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

4/68 Corrosion Index
nonaggressive corrosion. Because the evaluator foresees the rection program is poor. Perhaps an argument can be made that
evaluation of a line in a similarly dry, but also cold climate, high scores in coating and application place less importance on
he awards points for condition F: pt adjusted for higher temper- inspection and defect correction. This would obviously be a
atures = 1.9 points. (He plans to score the dry, cold climate as sliding scale and is probably an unnecessary complication. An
2 pts.) evaluation scale could look like this:
These evaluations therefore yield the following rank order
and relative magnitude: Good
Fair
Louisiana 0.4 pt Poor
Colorado 1.6 pts Absent
Arizona 1.9 pts
Coatingfitness (weighting: 50% ofcoating evaluation)
The evaluator sees little difference between conditions in
Colorado and Arizona, from an atmospheric corrosion view- Coating qualit?, Evaluate the coating in terms of its appro-
point, but feels that conditions around the line in south priateness in its present application. Where possible, use data
Louisiana are roughly four times worse. from coating stress tests or actual field experience to rate the
quality. When these data are not available, draw from any simi-
lar experience or from judgment.
A3. Atmospheric coating (weighting: 30% of
atmospheric corrosion) Good-A high-quality coating designed for its present envi-
ronment.
The third component in this study of the potential for atmos- Fair-An adequate coating but probably not specifically
pheric corrosion is an analysis ofthe preventive measures taken designed for its specific environment.
to minimize the threat. Obviously, where the environment is Poor-A coating is in place but is not suitable for long-term
harsher, more preventive actions are required. From a risk service in its present environment.
standpoint, a situation where preventive actions are not Absent-No coating present.
required-a very benign environment-poses less risk than a
situation where preventive actions are being taken to protect a Note: Some of the more important coating properties include
pipeline from a harsh environment. electrical resistance, adhesion, ease of application, flexibility,
The most common form of prevention for atmospheric cor- impact resistance, flow resistance (after curing), resistance to
rosion is to isolate the metal from the offending environment. soil stresses, resistance to water, resistance to bacteria or other
This is usually done with coatings. Coatings include paint, tape organism attack. In the case of submerged or partially sub-
wraps, waxes, asphalts, and other specially designed coatings. merged lines, marine life such as barnacles or borers must be
For aboveground components, painting is by far the most com- considered.
mon technique.
No coating is defect free, so the corrosion potential will Application Evaluate the most recent coating application
never he totally removed, only reduced. Note that, at this point, process and judge its quality in terms of attention to pre-
the evaluator is making no judgments as to whether a high- cleaning, coating thickness, the application environment (con-
quality coating or inspection program is needed. That detenni- trol of temperature, humidity, dust, etc.), and the curing or
nation is made when the attributes of facilities and atmosphere setting process.
type are combined with an assessment of these preventions.
Good-Detailed specifications used, careful attention paid to
Coating evaluations all aspects ofthe application; appropriate quality control sys-
tems used.
Coating effectiveness depends on four factors: Fair-Most likely a proper application, but without formal
supervision or quality controls.
1. Quality of the coating Poor-Careless, low-quality application performed.
2. Quality of the coating application Absent-Application was incorrectly done, steps omitted, envi-
3. Quality of the inspection program ronment not controlled.
4. Quality of the defect correction program.
Coating condition (weighting: 50% of coating
The first two address the fitness of the coating-its ability evaluation)
to perform adequately in its intended service for the life of
the project. The second two address the current condition of the Inspection Evaluate the inspection program for its thor-
coating-how it is actually performing. oughness and timeliness. Documentation may also be an inte-
For a general, qualitative evaluation, each of these compo- gral part of the best possible inspection program.
nents can be rated on a4-point scale: good, fair, poor, or absent.
The point values should probably be equivalent unless the eval- Good-Formal, thorough inspection performed specifically
uator can say that one component is of more importance than for evidence of atmospheric corrosion. Inspections are per-
another. A quality coating is of little value if the application is formed by trained individuals using checklists at appropriate
poor: a good inspection program is incomplete if the defect cor- intervals (as dictated by local corrosion potential).