Effective Maintenance Painting Practices for Offshore Oil & Gas Structures – Part Two

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The following sidebars supplement this article by Mark B. Dromgool of KTA-Tator Australia Pty Ltd, which appeared in JPCL, February, 2015.

Items to Avoid: As a general rule don’t prepare and paint

•    Handrails;
•    Lighting poles;
•    Bolts and fasteners (except where coincidental to corroded vulnerable items);
•    Electrical conduits;
•    Sight glasses, gauges
•    Sheetmetal items
•    Actuators or control systems
•    Rust stained items or surfaces (if required, fix the cause of the staining, not the effect)
•    Valve handles or wheels
•    Pipeline spades

Do's and Don’ts for Contractors
in the Three Pillars of Maintenance Painting Practice

•    Use various surface preparation tools as appropriate to remove any loose and flaking paint, and to dislodge all practical levels of corrosion.

•    Don’t polish the surface by undertaking excess surface preparation.

•    Achieving a fully oxide-free surface will not be necessary in most instances.  Sound, tight rust and islands of coating that are intact and are unlikely to dislodge can be accommodated.

•    Extensive time spent on surface preparation can be compensated for (to some degree) by enough coating material.

•    Extensive surface preparation effort on bolts and studs is not required — concentrate on the flange and pipe rather than the bolts or nuts. However, paint the bolts and nuts to assist on extending their life.

•    Extensive surface preparation effort on operating handles or valve wheels is not required.

•    Do not remove sound coating adjacent to the spot repair zone.

•    Feathering (as a general rule) is not required. Achieve a hard, sound edge and be careful with the brush application to stripe along the coating boundary.

•    A surface-tolerant epoxy coating will cope with a slightly lesser standard of cleaning, if enough coating is applied and is applied properly.

•    Lower the salt levels to the best practical level. This may require washing before commencement and certainly after surface preparation is complete. A bucket and a brush can be quite effective. Don’t use salt extraction “agents,” just potable water.

•    Allow cleaned and washed surfaces to dry as much as possible. Use compressed air if needed.

•    If practical, arrange the working day so that paint application can be performed during the middle of the working day, not last thing in the afternoon. This allows plenty of time for correct and full coating application and inspection without rushing. For winter work, painting after lunch is ideal as it allows the coating to cure when the conditions are ideal and not be subject to dropping overnight temperatures. Start doing surface preparation on other areas until the end of the day which can be freshened up in the morning.

•    Apply the surface-tolerant epoxy at an appropriate high film build to the bare steel and partly-coated areas plus about 20 to 25 mm out onto sound coating. Don’t prime over good sound coating so the zone that needs film build in subsequent coats is readily discernible. More new paint added over sound existing coating material that is already thick enough provides no additional value and can risk disbondment due to additional stress.

•    Concentrate on achieving full coverage with the primer and in achieving an appropriate film build.  Appearance is not a priority. Apply paint generously into the gaps between flange faces.

•    If valve handles or wheels have been cleaned or are rusty, prime with aluminum surface-tolerant epoxy, but thickness is not as vital as on pressure items.

•    Check DFTs on bare areas after the first coat to establish conformance.

•    Attempt to do most recoating within 48 hours to avoid having to reclean between coats.

•    Use an alternate color of the surface tolerant epoxy as the intermediate and subsequent coats. Confine this to the areas primed with aluminum-pigmented primer (plus a further small overlap onto sound coating).

•    Paint the second and subsequent coats to achieve full coverage and to provide a high resulting DFT on the surfaces that do not have an existing sound coating.

•    Check DFTs on bare areas to establish conformance. Achieve the specified minimum DFT before extending the paint coats beyond any spot-prepared zones.

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