8.2. Inspection of steel work (Pre-blasting preparation)

When a new construction is made or when maintenance work includes steel exchange or blast cleaning the steelwork must be checked for:

• Rounding of sharp edges.

• Smoothing of rough welding seams.

• Removal / grinding of weld spatter and beads.

• Cracks and pittings.

• Surface faults like laminations etc.

This work should be done according to the specification or ISO 12944-3 (Design considerations), and should be done in the welding shop before handling over for surface preparation and painting.

Figure 8.1.

Edges must be rounded and weld

spatter must be removed prior to the surface preparation

Figure 8.2.

Rounding of sharp edges is important to obtain an

even paintfilm over the entire surface

8.3. Inspection of surface preparation.

Inspection of surface preparation includes the following:

1. Cleanliness. Solvent cleaning to remove salt, oil, grease and dust/dirt

1. Evaluation of present condition (rust grade)

1. Surface preparation (preparation grade and roughness)

1. Cleanliness after surface preparation (salts, oil and grease)

1. Climatic conditions

As seen from the above cleanliness must be inspected twice. The first time (point 1 above) is solvent cleaning (according to SSPC-SP1), primarily to remove oil, grease, dust and dirt. Solvent cleaning often involves water that will be able to remove water-soluble salts as well. The second inspection (point 4 above) is to verify the cleanliness of the substrate prior to application of the paint.

8.3.1. Cleanliness. Solvent cleaning, sspc-sp1.

According to different standards the surfaces should more or less be free from all kinds of contaminants prior to further surface preparation or painting. It is impossible to remove oil / grease and salts by blast cleaning or mechanical cleaning. This necessitates the introduction of an additional cleaning procedure: Solvent cleaning.

Table 8.1. Methods for solvent cleaning.

To be removed	Procedure	Remarks 1)
Grease and oil	Water cleaning Steam cleaning Emulsion cleaning Alkaline cleaning Organic-solvent cleaning	Fresh water with addition of detergents. Pressure (< 70 MPa) may be used. Rinse with fresh water. Fresh water. If detergents are added, rinse with fresh water. Rinse with fresh water Aluminium, zinc and certain other types of metallic coating may be susceptible to corrosion if strongly alkaline solutions are used. Rinse with fresh water. Many organic solvents are hazardous to health. If the cleaning is performed using rags, they will have to be replaced at frequent intervals as otherwise oily and greasy contaminants will not be removed but will be left as a smeared film after the solvent has evaporated.
Water-soluble contaminants, e.g. salt	Water cleaning Steam cleaning Alkaline cleaning	Fresh water. Pressure (< 70 MPa) may be used. Rinse with fresh water Aluminium, zinc and certain other types of metallic coating may be susceptible to corrosion if strongly alkaline solutions are used. Rinse with fresh water.

¹⁾ Remark: Organic solvent cleaning will not remove water-soluble salts. Salts present at the surface must be removed by additional cleaning with fresh water.

According to SSPC-SP1, solvent cleaning is a method for removing all visible oil, grease, soil, drawing and cutting compounds and other soluble contaminants from the surface. The intention is to carry out the solvent cleaning prior to the application of paint and in conjunction with surface preparation methods specified for the removal of rust, mill scale or old paint. The recommended procedure is to remove heavy oil or grease first by scraper and then remaining oil and grease by the most suitable methods given in the table above.

Methods for detecting oil and grease

• The easiest test for detecting oil /grease on a surface is the “water break method” (not a Standard), where a drop of water is added on to the prepared surface. The drop will spread out rapidly on the surface if no oil / grease is present, but will remain on the surface in a drop-shaped form in the presence of oil / grease.

• Fettrot Test (Din 55 928 Part 4) using a 0,1 percent solution of Fettrot B.B. in ethanol can provide rapid visual indication of oil/grease on the surface.

• Also UV-light will detect oil/grease on the surface, which will give fluorescent blue light.

There is no quantitative test for oil or grease available, only qualitative tests.

Method for detecting salts.

When a structure is washed, water-soluble salts brought in contact with the water will automatically be removed. However, salts hidden under heavy deposits will not be dissolved. These deposits can not be washed off and have to be removed by the surface preparation prescribed (blast cleaning, water jetting etc.). As a consequence of this the amount of salt on the surface is not checked/controlled at this stage of the production, but is a critical part of the inspection prior to application. How to detect and remove them is therefore explained later in this chapter.