Cleaning with mechanical bare metal tools (SSPC- SP11)
In industry, situations are constantly arising in which high durability of the coating protection scheme is required and a white metal grade surface preparation is demanded, without the use of abrasive blasting being allowed. In these cases, we can resort to the use of the SSPC-SP11 standard, which is an easy and practical methodology to implement.
It is important to know this alternative since it allows to assure the quality of the surface preparation and therefore a good performance of the coating.
This procedure is very common as a surface preparation for 100% solids as in the case of welded joints of pipes, tanks and equipment and it is found all the time in the work specifications of the clients of the oil and gas sector and even in infrastructure and construction, however, it can be implemented in any coating work.
OBJECTIVES OF THE SSPC-SP11 STANDARD
It aims to leave the metal bare and generate a roughness profile according to the specification requirements of a protective coating to ensure its durability. It consists of a cleaning in which the following are removed: all calamine, rust, paint and any foreign material from the surface by mechanical means or power tools.
The height of the roughness profile will be a minimum of 1 mils but finally it will be defined by the requirements of the technical specification of the coating to be used and consequent with the dry film thickness of the same.
All surface preparation for high performance coatings includes aspects of cleanliness as well as roughness. In the specific case of SSPC-SP11 preparations, it must be considered that it is a low performance operation compared to the performance obtained through an abrasive blasting preparation. For that reason, equipment and tools must be selected to obtain the compliance of the specification requirement with the lowest cost and in the shortest time possible, in short, to aim at the highest productivity since the man hour has an important weight in the total costs of this preparation.
The best recommendation at present for cleaning purposes is the use of 3M Clean and Strip discs. This disc can be used in conventional polishers up to 11,000 RPM obtaining a white metal without generating relief or wounds by grinding in the steel, this disc uses 3M's patented Cubitron technology.
For the effect of the roughness that this SSPC-SP11 surface preparation requires, it is recommended to generate the roughness profile by means of reamers with tungsten carbide cutters and depth adjustment to regulate the roughness profile according to the requirement given by the specification. Profiles of up to 7 mils can be obtained in steel.