Industrial Protective Coatings And Linings

Industrial Protective Coatings And Linings Corrosion Inspection Management

The word “coating ” is a generic term and includes “paint.” In the most general terms, a “coating” is protection against corrosion, whereas a “paint” may have additional properties such as color or ultraviolet screening pigments. The terms “coating ” and “paint” are used interchangeably most of the times.

Other terms often used together are “ coatings” and “linings.” In general, when describing the interior surfaces of pipes or tanks, the term “linings” is used to identify the interior

surfaces and “coatings” is used to identify the exterior surfaces.

Protective or industrial coatings are the primary means employed to control corrosion.

PAINTS AND COATINGS of all types are widely used to provide color and pleasing aesthetics, and to prevent deterioration of the underlying substrate when exposed to various environments. Corrosion control with protective coating is the primary means employed to control corrosion.

In order, to apply corrosion control with protective coating, the protective coating must remain intact and adherent on the surface of any corrosive material.

Service Exposure:

corrosion protection coatings are specified by service exposure or the environment the coating will be subject to. The following are the basic service exposures defined:

• Atmospheric - Indoors, Outdoors

• Buried

• Immersion

• Complete, partial, or fluctuating immersion conditions

• Atmospheric exposure subject to condensation, high humidity, splash, or spray

• The following sub-exposure conditions may apply to any of the above:

Direct sunlight or UV: several coatings, such as epoxies, will deteriorate by chalking when exposed to sunlight. Chemical resistance: exposures may include acidic or alkaline concentrations, industrial smog, acid rain, sewage, or specific chemicals. The coating formulation is generally based on organic, inorganic, polymer, and copolymer chemistry. The diagram on the next page indicates what chemistries are generally provided and their suitability for a particular temp. range.

Protective Coating Component

All organic coatings consist of three basic components:

(1) solvent,

(2) Resin, and

(3) pigment.

Not all coating s contain solvent and pigmented components. There are solvent-free (100 % solids) coatings and clear, pigment-free coatings, but not resin -free coatings. Coating chemical formulators commonly group solvent, resin, and pigment components into two general categories.

The first category combines the solvent and the resin together. The solvent portion is called the “ volatile vehicle,” and the resin portion is called the “nonvolatile vehicle.” The combination of the solvent and the resin, where the resin is dissolved in the solvent, is called the “vehicle.”

The second category is the pigment. Pigments are additives that impart specific properties to the coating and are subdivided into two general categories:

(1) color and

(2) insert and reinforced.

When a coating is applied, the solvent evaporates during the curing process, leaving only the resin and the pigment components on the substrate. The remaining resin and pigments are sometimes called the “ coating solids,” and they form the protective film for corrosion protection.

(a) Solvent.—Organic solvents are formulated into coatings to perform three essential functions:

(1) dissolve the resin component;

(2) control evaporation for film formation; and

(3) reduce the coating viscosity for ease of application.

Solvents will also affect dry film adhesion and durability coating properties. In general, resins that are less soluble will require either more solvents or stronger solvents to dissolve the resins.

The terms “solvents” and “ thinners” are often used interchangeably, but there are distinctions within and between the two terms. The term “solvent” can imply two different usages:

(1) the solvent or solvent blends in the coating formulation at predetermined concentration levels; or

(2) cleaning solvents in strong concentration strength for cleaning brushes, rollers, hoses, and other equipment.

The usage of the term “thinner” (a thinner is a solvent) is most often associated with the coating applicator adding a thinner to a coating container to reduce the viscosity for ease of application. Adding thinner to a coating in the field is often called “field thinning.”

(b) Resin.— The resin (frequently called binder ) is the film forming component of a coating. Resins are typically a high molecular weight solid polymer that forms large repeating molecules in the cured film. The primary purpose of the resin is too wet the pigment particles and bind the pigment particles together and to the substrate (hence, the term “binder”). The resin imparts most of the coating properties. The various types of resins formulated in a coating will display distinct properties.

These properties are:

• Mechanism and time of curing

• Performance in-service exposure type

• Performance on substrate type

• Compatibility with other coatings

• Flexibility and toughness

• Exterior weathering

• Adhesion

No single resin can achieve a high degree of success in meeting the above coating properties with wide variations associated with each property. Therefore, generic coating types are generally classified by the primary resin type used in the coating formulation. Typical resins are acrylics, alkyds, and epoxy polymers.

Industrial Protective Coatings Linings Corrosion Inspection Management Asset Integrity, Reliability Maintenance, Plant Health Services, NDT

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