Introduction

Coating breakdown estimation is a skill that is difficult to master and an area prone to errors. In general, the amount of coating breakdown is overestimated as opposed to being underestimated resulting in the extent of rusting or other defects often being reported as being much higher than actual.

A number of standards are available to assist in the estimation of common defects such as blistering, rusting, cracking and flaking. These are discussed in the training unit on standards and in the training unit on common defects.

The Re Scale which is commonly used in paint performance guarantees is covered extensively in Unit 4 entitled “European Rust Scale”. Paint manufacturers also produce diagrams showing different extents of breakdown often distinguished as scattered or localized.

Introduction (cont)

The evaluation of breakdown of a coating by rusting is very subjective and probably the most difficult to assess with any degree of accuracy, particularly in internal spaces where illumination is poor and close access to the surface is not practical. A ships ballast tank is a prime example.

The assessment will vary from the simple ‘Good’, ‘Fair’, ‘Poor’ condition; the International Association of Classification Societies (IACS) method; to the more detailed evaluation required in the case of a coating failure investigation or a paint performance guarantee claim.

In the IACS method, the tanks are divided into a number of ‘areas under consideration’ as discussed in Chapter 2 and each area assessed individually as ‘Good’, ‘Fair’, ‘Poor’.

Introduction (cont)

The method does not average the results of the assessments of the areas under consideration but uses the area under consideration with the poorest rating to determine future inspection requirements.

A fore peak tank, for example, has three “areas of consideration” and would be rated as ‘Fair’ if one area was assessed as Fair and the other areas assessed as “good”, as illustrated in the diagram.

The same rating system can be used on cargo tanks, holds and other spaces.

IACS clarification of “GOOD”, “FAIR” and “POOR” coating Conditions.

The table is used in respect of crude oil tank coating condition except that the ‘breakdown of coating or area rusted’ is <5% for ‘Good’ and 5 – 20% for ‘Fair’.

Although good and poor conditions are relatively straightforward to assess, the fair condition often gives rise to disagreements between parties.

Classification Societies

Classification Societies provide photographic examples of tank coatings in the Good, Fair and Poor categories, often accompanied by an estimate of percentage breakdown and schematic diagrams. Some photographic examples are shown in the following pages

Irrespective of the method used in the assessment care should be taken not to confuse rust staining with actual coating breakdown as large areas of rust staining can emanate from a relatively small area of breakdown.

When the reason for the survey is in relation to a claim under a paint performance guarantee or an investigation into a coating failure, a more precise estimation of percentage breakdown may be required. The division of a large space into smaller more manageable areas will make evaluation easier and more precise. Guarantees often have an area exclusion, so the actual area of, e.g. Re2 needs to be recorded and worked out as a % of the whole tank.

Classification

Examples of tank coatings:

Good Condition

Classification

Examples of tank coatings:

Good Condition

Classification

Examples of tank coatings:

Fair Condition

Classification

Examples of tank coatings:

Fair Condition

Classification

Examples of tank coatings:

Poor Condition

Classification

Examples of tank coatings:

Poor Condition

Diagrams and Rust Scales

Diagrams and rust scales are available to assist the surveyor, and some examples are shown.

This table illustrates scattered coating breakdown.

1. 0.3%
2. 1%
3. 3%
4. 5%
5. 10%
6. 15%
7. 25%

Diagrams and Rust Scales

Diagrams and rust scales are available to assist the surveyor, and some examples are shown.

This table illustrates localised coating breakdown.

1. 0.3%
2. 1%
3. 3%
4. 5%
5. 10%
6. 15%
7. 25%

Alternative Assessment Diagrams

This ‘spotted’ diagram table has been used for many years and uses coloured spots of various sizes to illustrate percentages:

0.1%

0.3%

0.5%

1%

2%

5%

10%

20%

25%

Percentage Assessment

A possible method to assist in the assessment of the percentage of an area affected by coating breakdown can be to visually or digitally move all the breakdown areas into a corner of the photograph where it can be evaluated more easily.

The photographs on the following pages illustrate the technique.

Estimate of Percentages

~0.5% percentage over an area and then pushed into the corner.

Both areas have the same percentage of breakdown/corrosion etc.

Estimate of Percentages

~1.0% percentage over an area and then pushed into the corner.

Both areas have the same percentage of breakdown/corrosion etc.

Estimate of Percentages

~3.0% percentage over an area and then pushed into the corner.

Both areas have the same percentage of breakdown/corrosion etc.

Estimate of Percentages

~5.0% percentage over an area and then pushed into the corner.

Both areas have the same percentage of breakdown/corrosion etc.

Estimate of Percentages

~10.0% percentage over an area and then pushed into the corner.

Both areas have the same percentage of breakdown/corrosion etc.

Estimate of Percentages

~15.0% percentage over an area and then pushed into the corner.

Both areas have the same percentage of breakdown/corrosion etc.

Summary

Within this training unit we have reviewed different types of standards and charts used to assess specific percentages when surveying a coating to identify the condition.