Coal Tar Epoxy Polyamide, Black (or Dark Red) Coating

Applying Coal Tar Epoxy Polyamide, Black (or Dark Red)

PAINT SPECIFICATION NO. 16 – Coal Tar Epoxy Polyamide, Black (or Dark Red) Coating

1. Scope
This standard covers a two-component coal tar epoxy polyamide black (or dark red) coating for structural steel.

2. Description
2.1 The coal tar epoxy polyamide black (or dark red) coating consists of two parts. Component A contains a refined coal tar pitch, a liquid-type polyamide resin, and a polyamine promoter to accelerate curing rate. Component B is a liquid-type epoxy resin that is mixed into Component A just prior to application. Details of the composition are given in Table 1.

2.2 This coating contains approximately 71 percent by volume (vol. %) of nonvolatile film-forming solids (pigment and binder). The theoretical spreading rate for a 200 micrometer (8 mil) dry film thickness is 3.5 square meters/liter (142 square feet/U.S. gallon). Actual spreading rates can be significantly lower.

2.3 This coating is suitable for exposures in Environmental Zones 2A (frequently wet by fresh water), 2B (frequently wet by salt water), 2C (fresh water immersion), 2D (salt water immersion), 3A (chemical, acidic), 3B (chemical, neutral), and 3C (chemical, alkaline); and is intended for spray application over steel surfaces prepared in accordance with SSPC-SP6, “Commercial Blast Cleaning” (for non-immersion service), SSPC-SP 10, “Near White Blast Cleaning” (for immersion service), or SSPC-SP 8, “Pickling.” The protective coating is self-priming and exhibits good adhesion to clean structural steel and concrete surfaces. Adhesion of the coating to smooth surfaces such as cold-rolled steel or intact mill scale has been found to be substantially inferior to that attained on blast roughened surfaces (see Note 8.1).

3. Referenced Standards
3.1 The latest issue, revision, or amendment of the refer­enced standards in effect on the date of invitation to bid shall govern, unless otherwise specified. Standards marked with an asterisk (*) are referenced only in the Notes, which are not requirements of this specification.

3.2 If there is a conflict between the requirements of any of the cited referenced standards and this specification, the requirements of this specification shall prevail.

3.3 SSPC STANDARDS AND JOINT STANDARDS:

3.4 ASTM INTERNATIONAL STANDARDS:
D 4 Standard Test Method for Bitumen Content
D 5 Standard Test Method for Penetration of Bituminous Materials
D 36 Standard Test Method for Softening Point of Bitumen (Ring-and-Ball Apparatus)
D 139 Standard Test Method for Float Test for Bituminous Materials
D 605 Standard Specification for Magnesium Silicate Pigment (Talc)
D 609 Standard Practice for Preparation of Cold-Rolled Steel Panels for Testing Paint, Varnish, Conversion Coatings, and Related Coating Products
D 1296 Standard Test Method for Odor of Volatile Solvents and Diluents
D 1475 Standard Test Method for Density of Liquid Coatings, Inks, and Related Products
D 1544 Standard Test Method for Color of Transparent Liquids (Gardner Color Scale)
D 1652 Standard Test Methods for Epoxy Content of Epoxy Resins
D 2415 Standard Test Method for Ash in Coal Tar and Pitch
D 3721 Standard Specification for Synthetic Red Iron Oxide Pigment

3.5 FEDERAL STANDARDS:
*MIL-PRF-23236 Coating Systems for Ship Struc­tures2

3.6 AMERICAN NATIONAL STANDARDS INSTITUTE (ANSI) STANDARD:
Z129.1 Hazardous Industrial Chemicals– Precautionary Labeling

4. Composition
4.1 Ingredients and proportions shall be as specified in Table 1 and in Sections 4.3 through 4.7 (see Notes 8.2 and 8.3).
4.2 Each component of this coating based on the specified ingredients shall be uniform, stable in storage, and free from grit and coarse particles.
4.3 Coal tar pitch used in this coating is defined as a product obtained from the distillation of high temperature crude coke oven tar, which in itself is a product obtained during the destructive distillation of coal in slot ovens operated at a temperature above 700 °C (1300 °F). The coal tar pitch shall be composed primarily of a complex combination of three or more membered condensed ring aromatic hydrocarbons.
4.4 The epoxy resin shall be a di-epoxide condensation product of bisphenol-A and epichlorohydrin with terminal epoxide groups.
4.5 The polyamide resin shall be a condensation product of a dimerized fatty acid in polyamines.
4.6 Acceptable gelling agents are organic derivatives of magnesium montmorillonite and hydrogenated castor oil. Acceptable activators, if used, are methanol, ethanol, or propylene carbonate (see Note 8.4).
4.7 The accelerator shall be 2,4,6-tri (dimethylamino­methyl) phenol.

5. Properties
5.1 The coal tar pitch used shall meet the requirements for one of the types listed in Table 2.
5.2 The epoxy resin shall be clear, shall be free of turbidity, crystals, and particulate matter; and shall meet the require­ments of Table 3.
5.3 The polyamide resin shall be clear, shall be free of turbidity and particulate matter, and shall meet the require­ments of Table 4.
5.4 Component A of this coating shall meet the require­ments of Sections 5.5 through 5.8.
5.5 ODOR: Shall be normal for the materials permitted (ASTM D 1296).
5.6 COLOR: The color shall be black or dark red (see Note 8.5).

5.7 The viscosity of Component A shall not exceed 160 poises when tested as follows:
Fill a container having a diameter and a height of not less than 7.6 centimeters [cm] (3 inches [in.]) and 9.5 cm (3.75 in.), respectively, to a depth of not less than 7.6 cm (3 in.) with a representative sample of Component A. Set up an RVT series Brookfield viscometer with a No. 7 spindle and with guard removed. Bring the sample to (and thereafter maintain) a temperature of 77 °F (25 °C) and stir vigorously for two minutes with a stiff spatula. Immediately after stirring, lower the viscom­eter until 1/2 of the “neck” mark on the spindle is covered. Run the viscometer at 100 rpm for one minute and take a reading of the position of the pointer on the dial. If the dial reading is 40 or less, the viscosity shall be considered to be 160 poises or less. If the reading is over 40, immediately start the motor and take additional readings at one-minute intervals. If one or more readings of 40 or less are obtained out of ten readings, taken at one-minute intervals, the viscosity of the material shall be considered to meet the viscosity requirement.

5.8 The non volatile content of Component A shall not be less than 77 percent by weight (wt. %) when tested as follows:
Place a stirrer made of stiff wire into a small disposable aluminum dish of about 5 cm (2 in.) in diameter and weigh to the nearest 0.1 mg. As rapidly as possible, place between two and three grams of Component A into the dish and weigh immediately to the nearest 0.1 mg. After weighing, spread the material over the bottom of the dish. Heat the dish, wire, and contents in a well-ventilated convection-type oven maintained at 103 to 107 °C (217 to 225 °F) for three hours. After the mate­rial has been in the oven for a few minutes, and periodically thereafter, stir the material. Cool in a desiccator, weigh to the nearest 0.1 mg, and calculate the percentage of nonvolatile on a weight basis.

5.9 PHYSICAL REQUIREMENTS OF THE MIXED COATING: The mixed coating shall meet the requirements of Sections 5.10 through 5.15.
5.10 ODOR: Shall be normal for the materials permitted (ASTM D 1296).
5.11 COLOR: The color shall be black or dark red (see Note 8.5).

5.12 SAG: The coating shall not sag when tested as follows:
Prepare approximately 500 mL of the material by thoroughly mixing 100 mL of Component B into 400 mL of Component A. Determine its viscosity immediately after mixing, using the same procedure outlined in Section 5.7, but employing a No. 5 spindle. If all of five readings taken at one-minute intervals are above 50, reduce the viscosity by adding the thinner in small increments until a reading of not greater than 50 is obtained. Press a strip of 1in. (2.5 cm) masking tape across the full width of a solvent-cleaned 7.5 cm x 15 cm (3 x 6 in.) cold-rolled steel panel. The tape shall be parallel to and centered on the shorter axis of the panel. Within five minutes after making the final check of viscosity, apply the material to the panel at a wet film thickness of at least 350 micrometers (14 mils). The application may be made with a doctor blade having a gap of approximately 635 micrometers (25 mils) or by brush. Immediately after applying the material, carefully remove the masking tape and stand the panel in a vertical position (with the bare strip horizontal) in a draft-free, 24 to 27 °C (75 to 80°F) location. Examine the panel after four hours. Sagging or running of the coating into the base area shall constitute failure of the material to pass the sag test (see Note 8.6). Save the mixed coating for the penetration and adhesion tests described in Sections 5.13 and 5.14, respectively.

5.13 PENETRATION: The coating shall pass the following test:
Select and solvent-spray clean two 7.5 x 15 cm (3 x 6 in.)cold-rolled steel panels in accordance with ASTM D 609. Assure that the panel is flat ± 25 micrometers (1 mil). Draw a coat of the coating mixed (including any thinning) for the sag test. The drawdown applicator shall be a nonmagnetic metal capable of spreading a film 50 mm (2 in.) or more in width, and shall have the clearance necessary to provide a total dry film thickness of 500 to 640 micrometers (20 to 25 mils) in two applications of approximately equal thickness. Using a wet film gage, confirm that the applied thickness is ± 25 micrometers (1 mil) of the requirement. After the first application, allow the film to dry 18 to 24 hours in a horizontal position at 24 to 27 °C (75 to 80 °F) and at a relative humidity of not over 60%.

Apply a second coat over and at right angles to the first, using freshly mixed coating prepared identically to that used for the first coat. (Save both coatings for preparing adhesion test panels.) Allow the second coat to dry in a horizontal position at 24 to 27 °C (75 to 80 °F). After 120 hours of curing, clamp the panel onto the table of the penetrometer (ASTM D 5) so that the needle is over an area which is within the prescribed thickness range (as measured by SSPC-PA 2), and determine the penetration, using a total load of 200 grams applied for five seconds at 25 °C (77 °F). The average of the three lowest out of five penetration readings, all taken within a one-centimeter square, shall not exceed 0.03 cm after 120 hours of curing.

5.14 ADHESION: The coating shall pass the following test:
Blast clean two steel panels (similar to those used in the penetration test) with a clean, 30 to 50 mesh nonme­tallic abrasive until a uniform, gray-white surface, with well-developed anchor pattern, is achieved. Blow off dust with a clean air blast. Brush apply one coat each of the two test batches of coating used for the penetration test panels, allowing the first coat to dry 18 to 24 hours at 24 to 27 °C (75 to 80 °F) air temperature before applying the second. Each coat shall be applied at a wet film thickness of 250 to 350 micrometers (10 to 14 mils). After the final coat has cured for 120 hours at 24 to 27 °C (75 to 80 °F), test the adhesion of the coating to the metal with a sharp knife. It shall strongly resist being removed from the metal. Also test the inter-coat adhesion by attempting to separate the coats with the knife. Any delamination of the two coats shall constitute failure.

5.15 POT LIFE: The coating shall pass the following test:
Mix 100 mL of Component B into 400 mL of Component A, both of which have been brought to a temperature of 24 to 27 °C (75 to 80 °F) before mixing. Pour the material at once into a pint tin can, seal tightly, and store at 24 to 27 °C (75 to 80 °F). Examine the material four hours after it was mixed. For its pot life to be considered satisfactory, the mixed material shall remain in a fluid condition, and, when thinned with no more than 100 mL of xylene (or where required, the recommended thinner), shall be lump-free and brushable (see Note 8.7).

6. Labeling and Packaging
6.1 Labeling shall conform to ANSI Z129.1.
6.2 Technical data shall be provided for at least all data elements categorized as “essential” in SSPC-Guide 13.
6.3 PACKAGING: Four gallons of Component A shall be packaged in a standard five-gallon container with a lug type removable lid. Component B shall be packaged to the full mark in a one-gallon can with friction lid. Other forms of packaging that provide the required ratio (4:1/A:B by volume) of components is permissible unless otherwise specified in the procurement documents.
6.4 DIRECTIONS FOR USE: The following directions for use shall be supplied with each container of coating:

Directions for Use of Coal Tar Epoxy-Polyamide Black (or Dark Red) Coating

This coating is intended for use both as a primer and finish coat(s) over steel that has been blast cleaned or blast cleaned and primed with a suitable inhibitive primer. It may be used on steel in chemical or marine environments, on buried tanks and pipes, on steel immersed in fresh or salt water, in tidal, splash, and weather zone exposures, and for interiors of tanks and pipelines containing crude oil, salt brine, or caustic soda.

To prepare the coating for application, add the entire contents of the epoxy resin (Component B) container to the previously stirred contents of the related container of base (Component A) and mix vigorously for at least two minutes with a power agitator equipped with a 7.6-cm (3-in.) or longer blade. Some thinning may be desirable for spray application. Use xylene or, where required, the recommended thinner and not more than 1.9 L (one-half-gallon) to an 18.9 L (five-gallon) batch should be added. Apply the coating as soon after mixing as practicable since the material will thicken substantially over a two-hour period and may set up in the pot within two to four hours during very warm weather unless cooled prior to or after mixing.

This coating is usually applied by spray in two coats to a dry film thickness of 406 micrometers (16 mils) at its thinnest spots. This requires a spreading rate of 1.5 square meters per liter (60 square feet per gallon) of unthinned coating. In actual practice, upwards of 305 micrometers (12 mils) wet coating will probably be required for each 203-micrometer (8­mil) coat to obtain the desired minimum thickness. The drying time between coats under normal coating conditions shall not exceed 72 hours. Long drying times between coats may cause poor inter-coat adhesion, and it is advisable in warm weather to reduce the maximum interval between coats. Under conditions of hot weather or direct sunlight, it may be necessary to limit the inter-coat drying period to 24 hours or less.

Abusive handling of pre-coated steel may cause damage to the coating. This is more noticeable at low temperatures or after extended periods of cure.

Airless spraying equipment capable of developing upwards of 14 MPa (2,000 psi) hydraulic pressure is satisfactory for applying this coating to simple flat or near flat surfaces and to medium to large diameter pipes. For application to complex surfaces, use heavy-duty conventional air atomization spray equipment. If the application is by brush, apply with a stiff brush heavily loaded with coating; apply quickly and smoothly, and avoid excessive brushing.

Do not apply this coating when the receiving surfaces or the ambient temperatures are below 10 °C (50 °F), unless it can reasonably be anticipated that the average ambient temperature will be 10 °C (50 °F) or higher for the five-day period subsequent to the application of any coat. At tempera­tures between 10 and 15 °C (50 and 60 °F), allow the mixed coating to stand at least 30 minutes prior to application.

Clean all equipment immediately after use with a suitable solvent. Such cleaning solvents as high-flash aromatic naphtha, xylene, or toluene are satisfactory for clean-up, but can be improved by adding 10 to 20% of methyl isobutyl ketone and 10% isopropyl or normal butyl alcohol.

7. Disclaimer
7.1 While every precaution is taken to ensure that all information furnished in SSPC standards and specifications is as accurate, complete, and useful as possible, SSPC cannot assume responsibility nor incur any obligation resulting from the use of any materials, protective coatings, or methods specified herein, or of the specification or standard itself.

7.2 This specification does not attempt to address problems concerning safety associated with its use. The user of this specification, as well as the user of all products or practices described herein, is responsible for instituting appropriate health and safety practices and for insuring compliance with all governmental regulations.

8. Notes
Notes are not requirements of this standard.
8.1 Coal tar epoxy polyamide coatings exhibit excellent adhesion to other primers such as vinyl butyral wash primers, some types of zinc-filled primers, and freshly-applied conven­tional (without coal tar pitch) epoxy resin primers. Adhesion of this coating to aged epoxy resin primers of any type is question­able. This coating, when used as a self-primed system, has a proven performance record. When used in severe exposures,a suitable inhibitive primer may prolong the life of the system.

8.2 The procurement documents should establish the responsibility, times and procedures for inspection, and any required affidavit certifying compliance with the standard.

8.3 Federal Standard MIL-PRF-23236 covers a coal tar epoxy coating whose curing component is not limited to any specific type. The standard is primarily of the performance type that requires that the materials meet certain quality assurance provisions, including one based upon an 18-month service test. The standard is intended primarily to provide coatings which are suitable for ship tanks used for fuel and salt water ballast, but there is little doubt that coal tar epoxy coatings meeting the specified requirements are of high quality and well suited for the broader applications commonly associated with coatings of this type. However, the federal standard does not contain provisions which assure that the coating will neces­sarily have application, inter-coat adhesion, low odor, strength, rapid curing rate, and properties comparable to those required by the SSPC standard.

8.4 With respect to the manufacture of the base compo­nent, it is suggested that the following points be kept in mind.

1.) Anti-sag characteristics of the mixed coating are largely determined by the degree of dispersion of the gelling agent. Where an organic derivative of magnesium montmorillonite type gelling agent is used, dampening with the activator prior to milling is believed to be helpful in obtaining a greater degree of anti-sag efficiency.
2.) The use of a low oil absorption type of filler may facilitate the attainment of a balance of properties such that viscosity and anti-sag requirements will be met.
3.) In order to provide some margin of processing freedom, the minimum nonvolatile content and the range in composition have been established at levels which permit an appreciable variation in the amount of solvent used in making up the base component. Also, the amount of gelling agent and activator to be used is specified only on an approximate basis.
4.) The polyamide resin as currently manufactured can vary in imid­azaline content which has an effect on the manufacturing and performance properties of the coating. Use of the polyamide resin meeting the requirements of this standard will reduce problems in these cases.

8.5 In as much as the coating does not lend itself to precise color matching or to the attainment of other than dark, dull shades of brownish-red, the purchaser should be careful not to specify a precise color that is impractical to produce.

8.6 If the system is applied in two coats, the drying time of the first coat should be held to a minimum. Application of the second and subsequent coats may be applied as soon as practicable providing their application will not cause sagging of the total film. Under some climatic conditions, excessive film thickness per coat (1,000 to1,700 micrometers [40 to 65 mils]) can result in solvent entrapment and film cracking.

8.7 The temperature of the two components of this epoxy polyamide coating at the time of mixing has a large effect on its pot life. They should be stored under ventilated cover during hot weather and protected from the direct sun before and after mixing insofar as practicable. In some cases, it may be desirable to have Component A packaged in white containers in order to assist in the control of heat buildup. During cool weather, provisions should be made to maintain the temperature of the mixed coating at above 15 °C (60 °F), and preferably above 20 °C (70 °F), if satisfactory atomization is to be obtained without excessive thinning.

PAINT SPECIFICATION NO. 16 – Coal Tar Epoxy Polyamide, Black (or Dark Red) Coating