External Flint-Coat Casing Coating Technical Data & Specifications
FLINT-COAT: the process that improves the bond between cement and casing. A coating of permanent resin applied to the pipe holds millions of jagged rock particles. When wet cement flows onto this roughened surface, it clings like reinforced concrete, resisting internal and external pressures, chemicals, cathodic protection, and high bottomhole temperatures. Separation of cement and casing is effectively blocked, and so is this principal avenue of communication.
Hydraulic Bond Strength (Data Table 1)
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Cement: API Class A Water: 5.2 gals. per sack Curing Temperature: 120° F Curing Time: 24 hours |
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| Hydraulic Bond PSI | ||
| surface finish | Dry | Mud Film |
| New Mill Varnished | 10-50 | 20 |
| Rusty | 350-450 | 20-50 |
| Sandblasted | 500-600 | 50-60 |
| Resin-Sand Coated (BOND-COATED) | 1200-1600* | 700-900* |
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*Casing-Cement bond did not fail. The actual cement sheath itself failed (approx. tensile strength of cement). |
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Shear Bond Strength (Data Table 2)
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Cement: API Class A Water: 5.2 gals. per sack Curing Time: 24 hours |
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Shear Bond Strength PSI Curing Temperature |
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| surface finish | 80°F | 100°F |
| New Mill Varnished | 74 | 84 |
| Sandblasted | 123 | 133 |
| Resin-Sand Coated | 2400 | 2000 |
| *Data Table 2 courtesy of Halliburton Services New Techniques for Improving Cement Bond, By Evans & Carter, API Drilling & Production Practices, 1964 |
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Chemical Resistance of Resin-Flint Coating (Data Table 3)
| Type Fluid | Percent | Exposure at 80°F - 7 days |
| ACID | ||
| Acetic | 5 | Excellent |
| Citric | 10 | Excellent |
| Lactic | 5 | Excellent |
| Hydrochloric | 37.5 | Good (discoloration) |
| Sulfuric | 50 | Excellent |
| Nitric | 10 | Excellent |
| Phosphoric | 85 | Fair (surface attack) |
| Hydrochloric-Hydrofluoric | – | Good (discoloration) |
| ALKALI | ||
| Sodium hydroxide | 50 | Excellent |
| Ammonium hydroxide | 10 | Excellent |
| SOLVENT | ||
| Toluol | Excellent | |
| Mineral spirits | Excellent | |
| Sour crude oil | Excellent | |
| Butyl acetate | Excellent | |
| Ethyl alcohol | Excellent | |
| Methyl isobutyl ketone | Excellent | |
| Chloroethane | Excellent | |
| MISCELLANEOUS | ||
| Tap Water | Excellent | |
| Sodium hypochlorite | 5 | Excellent |
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*Data Table 3 courtesy of Halliburton Services New Techniques for Improving Cement Bond, By Evans & Carter, API Drilling & Production Practices, 1964 |
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Cathodic Protection
In addition to the excellent resistance of the resin coating to acids, bases and solvents shown in Data Table 3 high current densities applied to casing for cathodic protection against corrosion does not effect the cement bond. Test specimens were placed in salt-mud environment for periods up to 4 months at current densities considerably higher than would be run in normal field operations. No reduction in bond strength was observed under these extreme conditions.
Temperature
Regular resin coating is capable of withstanding bottomhole temperatures up to 350-400°F. Special High Temperature formulation is available up to 700°F. This coating has application in steam injection and hot waterflood type operations. From this corrosion control and prestressed pipe.
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