Quality control of the coating of structural steel, however, encounters some unique factors. Most paint coatings are, remarkably tolerant of variations in application conditions and procedures However, it is generally impossible to tell from the appearance of the coating whether it has been applied over a suitable surface. There are, as yet, no positive tests that can be applied to a paint film in situ that will provide this assurance.
One problem is the manner in which coatings fail. Loss of adhesion, visible corrosion, blistering, etc., which occur within a year or two of application are obvious faults. It is in everyone’s interest to avoid such failures, particularly since adequate repair work is nearly always more expensive and troublesome than the initial work and almost inevitably to a lower standard.
As with all quality control activities, they must be carried out independently of those involved in production, i.e. the operators carrying out surface preparation and coating application. These operators should, of course, be properly supervised and carry out their work to meet the contract requirements. However, they may have priorities other than those provided by the technical specification, not least the meeting of deadlines and payment on the basis of the amount of work done in a given time.
There is, therefore, often a genuine conflict between quality and production something not unique to coating processes. The performance of coatings that have been subjected to inspection depends upon four cornerstones: good specifications, Quality materials, qualified contractors and effective inspection.
Failure in any of these areas, like the weak link in the chain, will result in decreased performances and increased costs – often substantial. Generally, any inspection is preferable to none, although there are exceptions to this; for example, where inspection reaches a level of incompetence that leads to either unnecessary delays, possibly entailing considerable additional costs, or a failure to apply the correct technical procedures.
In some cases it could be said with some truth that ‘poor inspection is worse than no inspection.