Page 91 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Scoring the corrosion potential 4/69
Fair-Informal inspections, but performed routinely by quali- Holidays
fied individuals. Adhesion
Poor-Little inspection; reliance is on chance sighting of prob- Abrasion resistance
lem areas. Shear
Absent-No inspection done. Impact resistance.
Note: Typical coating faults include cracking. pinholes, In some cases, a more detailed evaluation ofcoating condi-
impacts (from sharp objects), compressive loadings (stacking tion might be warranted. An example list of variables for this
of coated pipes, for instance). disbondment, softening or flow- more rigorous evaluation is as follows:
ing. and general deterioration (ultraviolet degradation. for Atmospheric Coating Condition
example). Visual inspection results
The inspector should pay special attention to sharp corners Coating failures per square foot
and difficult shapes. They are difficult to clean prior to paint- Date of last visual inspection
ing, and difficult to adequately coat (paint will flow away from NDT inspection results
sharpness). Examples are nuts, bolts, threads, and some valve Thickness versus design thickness
components. These are often the first areas to show corrosion Holidays per square foot
and will give a first indication as to the quality of the paint job.
Chalking, cracking. blistering, flaking
Date ofNDT inspection
Correction ofdefects Evaluate the program of defect correc- DT inspection results
tion in terms of thoroughness and timeliness. Adhesion
Abrasion resistance
Good-Reported coating defects are immediately documented Impact resistance
and scheduled for timely repair. Repairs are carried out per Shear strength
application specifications and are done on schedule. Date of DT inspection
Fair-Coating defects are informally reported and are repaired
at convenience.
Poor-Coating defects are not consistently reported or Example 4.3: Scoring coating condition (Good)
repaired.
Absent-Little or no attention is paid to coating defects. In this section of aboveground piping, records indicate that a
high-quality paint was applied per NACE specifications. The
A more rigorous evaluation of coating condition would operator sends a trained inspector to all aboveground sites once
involve specific measurements of defects found adjusted by each quarter, and corrects all reported deficiencies at least
the time that has passed since the inspection and the use of spe- twice per year. The evaluator awards points as follows:
cial equipment during the inspection. Coating-good 3 pts
Nondestructive testing (NDT) performed during the inspec- 3
Application-good
tion includes a visual inspection. The visual inspection can Inspection-good 3
quantify and/or characterize the defects observed. Qualitative Defect correction-good 3
scales for such visual assessments can be found in National
Association of Corrosion Engineers (NACE) guidelines. NDT Average 3 pts
using special equipment can also quantify the coating thickness
and the extent of holidays. Current thickness can be compared Note; Twice per year defect correction is deemed appropriate
against design or intended thickness to assess the degradation for the section's environment.
or other inconsistency with design intent. If an electrical conti-
nuity tester is used the extent of holidays can be expressed in
terms of the voltage setting and number of indications or other
measurement of number and size of coating defects. Example 4.4: Scoring coating condition (Fair)
An NDT inspection rating scale can be established for a
more detailed evaluation. Table 4.2 provides an example. Here, a section contains several locations of aboveground
Destructive testing (DT) involves removing a sample of pipe components at valve stations and compressor stations.
coating or pipe and performing laboratory tests. Properties Touch-up painting is done occasionally at the stations. This is
investigated might include done by a general contracting company at the request of the

Table 4.2 Example NDT inspection rating scale

Blister
Rusting Blister size .f'equency Chalking Cracking Flaking
~
Good None None None None None None
Fair <lo% <1/8 in Medium Light Moderate 30%
Poor <33% <3/8 in Dense Complete Moderate 50"'o