History briefs:

In 2002, TSCF published “Guidelines for Ballast Tank Coating Systems and Surface Preparation” provided differing levels of standards for minimum target coating life of 10, 15 and 25 years (denoted as TSCF10, TSCF15, and TSCF25).
In order to address the same issue for all vessels, in 2006 IMO adopted Resolution MSC 215(82) “ Performance Standard for Protective Coatings for Dedicated Seawater Ballast Tanks in all Types of Ships > 500GT and Double-Side Skin Spaces of Bulk Carriers >150m ” (commonly referred to as PSPC).

This resolution came into force in 2008. PSPC is intended for a minimum target coating life of 15 years (which should make it the equivalent of TSCF15).

Note :  Major Conversions and FPSO’s are not covered by the standard

CONDITION OF STEEL SURFACE BEFORE/AFTER BLASTING

In mean of quality, the steel shall preferably be Rust Grade A or B  (ISO 8501-1).

The use of steel with Rust Grade C/D requires more tight inspection of surface profile after blasting as well as of possible salt contamination.

Blast-cleaning

Sa 1 Light blast-cleaning
Sa 2 Thorough blast-cleaning
Sa 2 1/2 Very thorough blast-cleaning
Sa 3 Blast-cleaning to visually clean steel

Hand and power tool cleaning

St 2 Thorough hand and power tool cleaning
St 3 Very thorough hand and power tool cleaning

If you have a rust grade A or B (mill scale on full or parts of surface) you need “heavy” (high density) grains to hammer the hard and brittle scale off the surface ( EXISTED AFTER ROLLING) . So a steel or chilled iron abrasive is the best choice. Higher pressure and less abrasive helps as well (higher speed of the single grains and as E = m/2 * v² )

On rust grade C or D (rust with/without scars) “lighter” abrasives like Slag (single-use) or garnet (reusable) should be used. Note: steel thickness on Grade D to be re-conform with structure specified configuration.

General view the requirement of Surface preparation as per PSPC on Shipbuilding.

Note on surface Power Tool St3 :

There are no minimum profile requirements are specified in the St3 standard

However…

• Where power tool preparation is used, in order to ensure satisfactory adhesion of the anti-corrosive coating, care should be taken to avoid “polishing” the welds and surrounding areas

The above introduction is the general concept of Painting inspector during the inspection.

For further detail standard and how to inspect after blasting, Pls see PSPC – Performance Standard for Coating of Ballast Tanks – Part 2