Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D1647-89 – Standard Test Method Technical Guide
The ASTM D1647–89 (Reapproved 1996) standard outlines two reliable methods for gauging the durability of dried varnish films. These tests are essential for a meaningful comparison of protective coatings exposed to water and mild chemical agents, bridging the gap between manufacturer specifications and end-user expectations in demanding environments.
📐 Specimen Geometry and Preparation
Test Method A (Water Resistance) utilizes bright tinplate panels measuring 3 by 5 inches (75 by 125 mm). These panels must be cut from commercial No. 31 gage (0.225 mm) stock, weighing 0.4 to 0.5 lb/ft² (1.90 to 2.50 kg/m²), and meticulously cleaned per Practice D 609. The varnish is flowed onto the panel and allowed to drain in a nearly vertical position.
Test Method B (Alkali Resistance) employs standard glass test tubes as substrates. The varnish is applied via a simple dipping process, ensuring a uniform coating for subsequent exposure to dilute alkali.
Both methods rely on standardized drying. Method A specimens dry for 48 hours, while Method B specimens are conditioned for 72 hours, both under the controlled atmosphere defined by Specification D 3924.
⚠️ Safety First: This standard does not address all safety concerns. Always establish appropriate safety and health practices for handling varnishes, solvents, and reagent chemicals before beginning the test procedure.
⚙️ Test Procedure and Conditions
In Test Method A, the dried panels are placed in a 600 mL glass beaker containing approximately 2.5 inches (65 mm) of reagent water (Type IV per D 1193) at room temperature. The ends that were uppermost during drying are immersed for the standard 18 hours. After removal, the panels are wiped carefully and allowed to dry at room temperature.
Test Method B involves suspending the coated and dried test tubes in a dilute sodium hydroxide solution. Exposure times range from 1 to 24 hours. Following exposure, the tubes are rinsed, dried for 30 minutes, and examined visually for any degradation.
| 📏 Parameter | 💧 Water Resistance (Method A) | 🧪 Alkali Resistance (Method B) |
|---|---|---|
| Substrate | Bright Tinplate (No. 31 gage) | Glass Test Tubes |
| Dimensions / Gage | 3 x 5 in. / 0.225 mm | Standard lab tubes |
| Drying Period | 48 hours (D 3924) | 72 hours (D 3924) |
| Immersion Medium | Reagent Water (D 1193 Type IV) | Dilute Sodium Hydroxide |
| Standard Duration | 18 hours (or as agreed) | 1 to 24 hours |
| 🟦 Evaluation Criterion | 🎯 Metric |
|---|---|
| Film Recovery | Time for whitening to disappear |
| Surface Disturbance | Presence of blooming or blushing |
💡 Critical Metric: When evaluating water resistance, carefully note and record the time required for any whitening of the film to disappear after removal from the water bath. This recovery time is a direct indicator of the coating’s resistance to water ingress.
📊 Key Measured Properties
The evaluation of both test methods is fundamentally visual. The primary properties observed are whitening and blooming. The standard specifically instructs the technician to “note the time required for whitening, if any, to disappear” as it is a key indicator of the film’s ability to recover from exposure. Blooming, which is a haze or milky appearance, is another critical failure mode. Together, these observations form a reliable basis for comparing the performance of different varnish systems against water and alkali exposure.
❓ Frequently Asked Questions
🔍 What is the standard immersion time for water resistance testing? The standard immersion time for Test Method A is 18 hours in reagent water at room temperature, although alternative times can be agreed upon between the purchaser and seller.
💡 What type of water is required for ASTM D1647 Test Method A? The standard requires reagent water conforming to Type IV of ASTM Specification D 1193.
⚡ How are the tinplate panels prepared for the water resistance test? Panels must be carefully cleaned and dried before use in accordance with Methods B or C of Practice D 609.
📌 What is the purpose of the “72-hour” drying period in Test Method B? The extended 72-hour drying period for the alkali resistance test ensures the varnish film is thoroughly cured and conditioned before exposure to the dilute sodium hydroxide solution, promoting consistent and reproducible results.