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D5515-22 – Standard Test Method Technical Guide
📐 Scope and Fundamentals
The D5515-22 standard, “Determination of the Swelling Properties of Bituminous Coal Using a Dilatometer,” specifies a precise laboratory procedure for measuring the expansion characteristics of bituminous coal. This test method is specifically applicable to coals exhibiting a Free Swelling Index (FSI) of 1 or greater, as determined by Test Method D720.
The core principle dictates that the final volume of char produced during the dilatation test is directly dependent on both the mass of coal within the test pencil and the internal radius of the retort tube. To ensure reproducibility, D5515-22 incorporates a correction using the air-dried coal pencil mass (Mdry) and the measured average retort tube geometry.
💡 Technical Note: Values stated in SI units are regarded as the standard per Section 1.3 of the method. Users must also establish appropriate safety, health, and environmental practices before application.
⚙️ Test Procedure and Methodology
The procedure centers around the preparation and measurement of a coal pencil. The standard specifies a trimmed pencil length of 60 mm. The method introduces a rigorous calculation for the air-dried coal pencil mass, accounting for any added water during preparation, which is a distinguishing feature compared to some international equivalents.
The test methodology addresses well-documented discrepancies found in older International Standards. For example, the Audibert-Arnu (ISO 349) method requires trimming the wider end of the coal pencil, while the Ruhr (ISO 8264) method specifies trimming the narrower end. This leads to systematically different results that are resolved by the mass-correction procedure in D5515:
| 🟦 Feature | 📐 D5515-22 (ASTM Standard) | 📐 Audibert-Arnu (ISO 349) | 📐 Ruhr (ISO 8264) |
|---|---|---|---|
| Pencil Trimming End | Mass-corrected procedure | Wider end | Narrower end |
| Percent Contraction | Corrected to air-dried mass | Higher | Lower |
| Percent Dilatation | Corrected to air-dried mass | Lower | Higher |
Key referenced documents for standard preparation and sampling include Practice D2013 (Preparing Coal Samples) and Practice D2234/D2234M (Collection of a Gross Sample).
📊 Key Measured Properties and Data
The standard reports coal expansion on an air-dried coal mass basis. The primary calculated property is the air-dried coal pencil mass (Mdry), defined as the calculated mass of the trimmed 60 mm long coal pencil corrected for added water, expressed in grams. This value, alongside the measured retort tube radius, is used to determine the true volumetric swelling behavior of the coal sample.
| 🎯 Parameter | ⚡ Requirement / Value |
|---|---|
| Applicable Coal Type | Bituminous Coal |
| Minimum Free Swelling Index | ≥ 1 (Test Method D720) |
| Trimmed Pencil Length | 60 mm |
| Key Correcting Factor | Air-dried coal pencil mass (Mdry) |
⚠️ Interlaboratory Caution: The standard explicitly notes that the Ruhr and Audibert-Arnu methods provide “consistently different values for percent dilatation and percent contraction.” D5515-22 mitigates this by standardizing the correction for coal mass and retort geometry.
❓ Frequently Asked Questions
🔍 What is the purpose of correcting for air-dried coal pencil mass (Mdry)?
The final volume of char is highly dependent on the mass of coal in the pencil. D5515-22 corrects the mass for any added water to standardize the test on an air-dried coal basis, eliminating a major source of variability found in other methods.
💡 How does D5515-22 differ from the Audibert-Arnu method (ISO 349)?
The Audibert-Arnu method specifies trimming the wider end of the coal pencil, while D5515-22 employs a specific corrective mass procedure to avoid the systematic biases (higher contraction, lower dilatation) associated with end-selection in the older ISO methods.
⚡ What are the standard qualification criteria for a coal sample in this test?
The test method is strictly limited to bituminous coals which have a Free Swelling Index (FSI) of 1 or greater, as determined by Test Method D720. Coals with an FSI of 0 are not suitable for this procedure.
📌 Why is the retort tube radius measured in D5515-22?
Because the final volume of char is dependent on the radius of the retort tube. Measuring this radius allows for precise calculation of the char volume, which is critical for accurately determining the percent contraction and dilatation.