Replica Tape ASTM D 4417

10.20.3 Replica Tape ASTM D 4417

require a surface profile of 1.5–3.5 mils (37–

Method C– NACE RP0287

87 µm). Surface profile is important because it increases the surface area and roughness to

Surface profile may be measured with rep- which the coating can adhere.

lica tape ( Figure 10.87 ), a proprietary prod- uct produced by the Testex® Corporation.

Too shallow a surface profile may result in Two types of tape are commonly used: premature coating failure due to lack of

adhesion, identified by peeling, blistering, or

• Coarse for 0.8–2.0 mil (20–50 µm) sur-

face profile

delamination. Too high a profile may have peaks that are inadequately covered, result-

• Extra coarse for 1.5–4.5 mil (37–112 µm)

ing in pinpoint rusting or rust spots. This surface profile most likely occurs when primers are applied

but left exposed without topcoats for some period of time. Good practice suggests applying at least two coats over the blast cleaned surface to ensure the surface profile is adequately covered.

In general, the greater the surface profile, the better coating adhesion will be. One excep- tion to this rule appears to be inorganic zinc silicate primers, which tend to split (lose cohesion) when the anchor profile exceeds

Figure 10.87 Replica Tape and Anvil Micrometer

about 2.5 mils (67 µm). Apply a piece of the tape (a small square of

This may be caused in part by attempts to compressible foam plastic attached to a non- increase coating thickness to cover profile

compressible plastic Mylar film) to the blast peaks. Inorganic zinc silicate primers are

cleaned surface, dull side down. Use a hard, well known to be sensitive to excess thick-

rounded object (burnishing tool), such as a ness. Follow the guidelines on the manufac-

swizzle stick ( Figure 10.88 ), to crush the turer’s technical data sheets.

foam into the blast cleaned surface. This causes the foam to form an exact reverse impression (replica) of the actual surface profile.

Surface Preparation 10-65

sensitive test, and although it can be used in the field, it is best used in the laboratory ( Figure 10.90 ).

Figure 10.88 Testex Tape and Swizzle stick

Figure 10.90 Digital Surface Profile Gauge

Other surface profile instruments, such as depth measuring microscopes, or diamond- point tracking stylus gauges, are sophisti- cated laboratory methods not commonly

used in the field (on site) or blast shop. Remove the tape from the surface. Use an

Figure 10.89 Replica Tape Procedure

10.20.5 Inspection Considerations

anvil micrometer ( Figure 10.89 ) to measure

Summary

the thickness of the foam and the plastic. The term surface preparation (often short- The thickness of the Mylar film, 2 mils (50 ened to surface prep) is broadly used to µm) is subtracted from the micrometer read- describe the process of preparing a surface ing, and the result is the surface profile for coating. As discussed earlier in this depth. course, inadequate or poor surface prepara-

Two standards describe the tion is the leading cause of premature coat- working method for using replica

ings failure in today’s industry. Hence, tape: NACE Standard RP0287

inspectors must take a comprehensive and ASTM D 4417, Method C

approach to inspecting the substrate prior to coating application. Regardless of the sub- strate, the inspector must be mindful of the

10.20.4 Digital Profile Gauge ASTM D

fact that protective coatings performance

4417 warranties rely heavily on the surface prep-

Rest the instrument base on the tops of the

aration results achieved prior to applica-

surface profile peaks; the spring loaded tip

tion.

projects into the valleys. This is detailed in ASTM D 4417, Method B. This is a very

10-66 Surface Preparation