Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.26 Use of solvents in the shipbuilding 1027
tion (up to 30 %) of the coatings are applied indoors. 10 Coating and cleaning operations constitute
the major source of VOC and HAP emissions from shipyards. If the metal surface is
not well prepared before a coating is applied or if the coating is applied at the wrong ambient
conditions, the coating system may fail and the work may have to be redone. The amount of
cleaning necessary will depend on the type and extent of the problem and the coating system
that is being used.
14.26.4 CLEANING OPERATIONS USING ORGANIC SOLVENTS
In most industrial applications involving metal substrates, organic cleaning solvents are
used to remove contaminants or undesirable materials from surfaces before a coating is applied
to clean equipment and parts utilized to apply the coating or soiled during that operation.
Solvents are used for general maintenance of equipment parts. These surfaces are
typically made of steel. However, vessels may also be made from natural materials such as
wood and synthetic materials such as fiberglass. Therefore, a solvent must be selected that
will not attack the substrate being cleaned.
For material accounting purposes, we can classify cleaning (unit) operations as follows:
11,12
1. Surface preparation of large manufactured components (stage before a coating is
applied).
2. Surface preparation of small manufactured components (stage before a coating is
applied).
3. Line cleaning (includes piping network and any associated tanks).
4. Gun cleaning (manually or in a machine).
5. Spray booth cleaning (walls and floor).
6. Tank cleaning (mostly inner tank surfaces and any associated pipes).
7. Parts (machine) cleaning (simple dip tanks and large machines).
8. Cleaning of equipment and other items (e.g., bearings, buckets, brushes, contact
switches).
9. Floor cleaning (organic solvents are no longer used).
These categories are similar to those found in other industries involved in the application
of surface coating. However, the number of cleaning categories varies from one industry
to another. For example, the automotive manufacturing industry (SIC code 3711) and
the furniture industry are involved to various degrees in all nine types of cleaning operations.
On the other hand, the photographic supplies (chemicals) industry will not include the
first three listed cleaning operations. 11
14.26.4.1 Surface preparation and initial corrosion protection
Large manufactured ship components are often cleaned with an organic solvent as the first
of a number of cleaning steps that are required before a coating is applied. The method of
surface preparation is selected to work with a chosen coating system. Surface preparation
may include application of chemicals such as etching agents, organic solvents cleaners, and
alkaline cleaners. Organic solvents such as mineral spirits, chlorinated solvents, and coal tar
solvents are used to remove unwanted materials such as oil and grease. 13 If a ship is being
repaired, existing coatings usually need to be removed. Solvents such as dichloromethane
are commonly used for removing (stripping off) old or damaged coatings. However, aqueous
systems involving caustic compounds are now being used more frequently for such purposes.
14 Pressure washing and hydro blasting are other cleaning techniques used. But, the