Page 109 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Scoring the corrosion potential 4/87
ance to bacteria or other organism attack. In the case of sub- Another indirect method was mentioned in this section’s
merged lines, marine life such as barnacles or borers must be introduction. A measure of the cathodic protection require-
considered. ments--especially the change in these requirements over
time-gives an indication of the coating condition (see Figure
Application Evaluate the most recent coating application 4.7 earlier).
process and judge its quality in terms of attention to pre-clean- The methods discussed above and other indirect observation
ing. coating thickness, the application environment (tempera- methods require a degree of skill on the part of the operator and
ture, humidity, dust, etc.), and the curing or setting process. the analyzer. Industry opinion is divided on the effectiveness of
some of these techniques. The evaluator should satisfy himself
Good-Detailed specifications are used, carefu! attention is that the operator understands the technique and can demon-
paid to all aspects ofthe application; appropriate quality con- strate some success in its use for coating inspection.
trol systems are used.
Fair-Most likely a proper application is done, but without for- Good-A formal, thorough inspection is performed specifi-
mal supervision or quality controls. cally for evidence of coating deterioration. Inspections are
Poor-A careless, low-quality application is performed. performed by trained individuals at appropriate intervals (as
Absen/-Application was incorrectly done, steps omitted, envi- dictated by local corrosion potential). Full use of visual
ronment not controlled. inspection opportunities in addition to one or more indirect
techniques being used.
An alternate approach to scoring coating fitness is to begin Fair-Inspections are informal, but performed routinely by
with a score for the type of coating, reflecting the coating’s per- qualified individuals. Perhaps an indirect technique is used
ceived future performance. This might be based on historical but maybe not to its full potential.
performance information or laboratory tests. Then. adjust- Poor-Little inspection is done; reliance is on chance sighting
ments are applied to this score for any conditions that might of problem areas. Informal visual inspections when there is
affect the coating’s ability to perform. The magnitude of an the opportunity.
adjustment should reflect its possible impact on coating per- Absent-No inspection done.
formance. Examples of adjustments are shown inTable 4.8.
Note: Typical coating faults include cracking, pinholes,
Coating Condition (weighting 50% of coating) impacts (sharp objects). compressive loadings (stacking of
coated pipes), disbondment, softening or flowing, and general
Inspection Evaluate the inspection program for its thorough- deterioration (ultraviolet degradation, for example).
ness and timeliness. Documentation will also be an integral part
of the best possible inspection program. Inspection of under- Correction ofdefects Evaluate the program of defect correc-
ground coating can take several forms. Opportunities for visual tion in terms of thoroughness and timeliness.
inspection will occasionally present themselves, as the pipe is
exposed for various reasons. When this happens, the operator Good-Reported coating defects are immediately documented
should take advantage of the situation to have trained personnel and scheduled for timely repair. Repairs are carried out per
evaluate the coating condition and record the findings. application specifications and are done on schedule.
A second inspection method, less direct than visual inspec- Fair-Coating defects are informally reported and are repaired
tion, impresses aradio or electric signal onto the pipe andmeas- at convenience.
ures this signal strength at points along the pipeline (Figure Poor4oating defects are not consistently reported or
4.9). The signal strength should decrease linearly in direct pro- repaired.
portion to the distance from the signal source. Peaks and unex- Absent-Little or no attention is paid to coating defects.
pected changes in the signal indicate areas of non-uniform
coating-perhaps damaged coating. This technique is called a The coating condition assessment can be made more data
holiday detection survev. Based on the initial survey, test holes driven if accurate measurements of cathodic protection current
are dug for visual inspection ofthe coating in order to correlate requirements exist. These measurements are usually in the form
actual coating condition with signal readings. of milli-amperes per square foot of pipeline surface area. A
Table 4.8 Adjustments to coating performance scores

Coating type
Age Adjustment that conservatively assumes ongoing coating deterioration.
Application Adjustment that penalizes field-applied coating because applicatlon conditions and surface preparation are more difficult
to control.
Damage potential
Coating environment Examines the potentlal harm to the coating from its immediate environment. Mechanlcal damage is main consideration:
rock impingement, soil stress, wave action, etc. Aseismic faultings and subsidences are areas of active soil movements
that can damage coating.
Coating protection Assesses the response to a potentially harmful environment-the forms of mitigation in place to minimize coating
damage potential.
Note: Points are assigned based on experience with life cycle of various coating types.