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D2416-20 – Standard Test Method Technical Guide
ASTM D2416-20 establishes a test method for determining the coking value of tar and pitch materials using a modified Conradson apparatus. Specifically designed for samples with an ash content not exceeding 0.5% (as detailed in Test Method D2415), this standard provides a highly reproducible alternative to the traditional gas-fired D189 method by employing a precisely controlled electric furnace. The residue remaining after vaporization and pyrolysis is reported as the coking value, a critical parameter for indicating the relative coke-forming propensities and evaluating the uniformity of the material.
📐 Apparatus and Material Specifications
The accuracy of the D2416 method is heavily dependent on the precise geometry and material composition of the specialized test assembly. The equipment consists of a specific sequence of nested crucibles, a wire support, and a hood, the critical specifications of which are outlined below.
| 🟦 Component | 📏 📐 Dimensions | 🎯 Capacity / Rating | ⚡ Material |
|---|---|---|---|
| Crucible (a) | 46 mm to 49 mm rim diameter | 29 mL to 31 mL | Porcelain or Silica (glazed) |
| Skidmore Crucible (b) | 37 mm to 39 mm height; 30 mm to 32 mm flat bottom O.D. | 65 mL to 82 mL | Flanged and Ringed Iron |
| Metal Crucible (c) | 78 mm to 82 mm O.D. (top); 58 mm to 60 mm height; ~0.8 mm thickness | ~25 mL sand layer | Spun Sheet-Iron or Nickel |
| Wire Support (d) | 65 mm triangle; 1.5 mm to 2.0 mm wire cross-section | Supports metal crucible cradle | Bare Nichrome Wire |
| Hood (e) | 120 mm to 130 mm diameter | Circular | Sheet-Iron |
💡 Critical Specification Detail: The Skidmore crucible features a horizontal opening of approximately 6.5 mm that must be kept unobstructed to regulate the air supply during pyrolysis. Additionally, the sand in the metal crucible must be dry and properly graded per E11, passing a 70 mesh (212 µm) sieve but retained on a 200 mesh (75 µm) sieve to ensure consistent thermal behavior.
⚙️ Test Procedure and Method Principles
The test procedure is designed to vaporize and pyrolyze the sample under strictly limited oxygen conditions according to the summary of the test method. A weighed sample is placed in the porcelain crucible (a), which is nested inside the Skidmore crucible (b). This assembly is then placed into the outer metal crucible (c), which contains a level layer of precisely graded sand to bring the Skidmore crucible nearly to the top. The entire assembly sits on the Nichrome wire support triangle (d) beneath the sheet-iron hood (e) and is subjected to a controlled heating cycle within the electric furnace for the specified duration and temperature.
⚠️ Safety and Regulatory Note: As stated in Section 1.4 of the standard, the user is responsible for establishing appropriate safety, health, and environmental practices. This includes managing the high temperatures of the electric furnace and the potentially hazardous fumes released during the pyrolysis of tar and pitch.
📊 Key Measured Properties and Significance
The primary output of the D2416 test is the Coking Value, expressed as a percentage of the original sample mass. This value is directly related to the material’s behavior during carbonization and is used for characterization and quality control.
| 📊 Property | 🟦 Description | 🎯 Application |
|---|---|---|
| Coking Value (wt%) | Mass of residue remaining after the standardized vaporization and pyrolysis process. | Indicates the relative coke-forming propensity of the tar or pitch. |
| Reproducibility | Results are practically identical to Test Method D189 but with significantly improved reproducibility. | Evaluating uniformity of shipments and characterizing sources of supply. |
❓ Frequently Asked Questions
© 2026 TNLab — This article is a technical interpretation for reference only. The original standard as published by ASTM International takes precedence.