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D5192 – Standard Test Method Technical Guide
The ASTM D5192/D5192M standard establishes the definitive practice for the collection and handling of coal samples derived from borehole cores. Following this procedure is critical for maintaining the in-situ integrity of the sample, ensuring that subsequent geological evaluation and laboratory analysis, conducted per standards like D2013/D2013M and D4371, yield accurate and representative results.
📐 Scope, Core Specifications, and Units
The scope of this practice is precisely defined in Section 1.1, covering the collection and handling of a coal sample specifically from a core recovered from a borehole. A fundamental requirement of the standard is the dual unit system. As stated in Section 1.2, values in SI units and inch-pound units are regarded separately as standard and must not be combined under any circumstances to ensure full conformance.
Section 3.1.5 provides the technical definition for the core itself: a cylindrical section of rock or coal, typically 5 to 10 cm in diameter, brought to the surface for examination and analysis.
| 🟦 Core Specification | 📏 Details from D5192 |
|---|---|
| Typical Diameter | 5 to 10 cm |
| Primary Recovery Tool | Two nested core barrels (outer rotating, inner receiving) |
| Preferred Barrel Type for Coal | Split-tube barrel |
| Functional Purpose | Geologic examination, representative sampling, and laboratory analyses |
⚠️ Critical Unit Requirement: Conformance with D5192/D5192M requires the independent use of either SI or inch-pound units. Combining values from the two systems is strictly prohibited per Section 1.2.
⚙️ Core Drilling Equipment and Geological Hazards
The standard distinguishes between the types of core barrels and the geological challenges that can compromise sample quality. The core barrel assembly (3.1.6) consists of an outer tube rotating with the bit and an inner tube that receives the core. The split-tube barrel (3.1.6.1) is emphasized as the preferred tool for coal. It is made of two longitudinal halves bound by reinforced tape, allowing the operator to access the intact core cleanly by cutting the tape.
Practitioners must also be vigilant for caves or washouts (3.1.3). These are zones of increased borehole diameter caused by rock fragments falling from the walls or differential erosion from the drilling medium. The standard warns that these zones can block the hole, contaminate cuttings, and significantly affect the accuracy of density geophysical logs.
| 🗺️ Geological Feature | 📝 Definition | ⚡ Impact on Core Recovery |
|---|---|---|
| Caves / Washouts | Zones of increased hole diameter from erosion or falling rock fragments. | Can block the hole, contaminate cuttings, affect density geophysical logs. |
| Concretion | Mineral mass in rock of different composition, deposited from aqueous solution. | Disrupts seam thickness measurement and representative sampling. |
💡 Best Practice for Coal Coring: Always utilize a split-tube barrel for coal seams. The design minimizes mechanical disturbance and preserves the structural integrity of the core, which is essential for accurate megascopic description and subsequent laboratory analysis.
📊 Key Referenced Standards and Terminology
The D5192 practice is integrated into the broader ASTM coal testing framework. It relies on several key standards for terminology and subsequent sample analysis as listed in Section 2. Accurate application of this practice requires familiarity with these references.
| 🔬 Standard | 📜 Title and Purpose |
|---|---|
| D121 | Terminology of Coal and Coke (Base definitions) |
| D388 | Classification of Coals by Rank |
| D1412 | Test Method for Equilibrium Moisture of Coal at 96 to 97 % Relative Humidity and 30 °C |
| D2013/D2013M | Practice for Preparing Coal Samples for Analysis |
| D4371 | Test Method for Determining Washability Characteristics of Coal |
| D4596 | Practice for Collection of Channel Samples of Coal in a Mine |
❓ Frequently Asked Questions
🔍 What is the standard diameter range for a coal core?
According to Section 3.1.5, the recovered core is usually 5 to 10 cm in diameter. This cylindrical section is brought to the surface specifically for geologic examination and representative sampling.
💡 How must units be treated to conform to this standard?
Section 1.2 is explicit: SI units and inch-pound units are regarded separately as standard. They are not exact equivalents, and values from the two systems shall never be combined to ensure conformance.
⚡ What are “caves” or “washouts” in a borehole?
Defined in 3.1.3, these are zones of increased hole diameter caused by rock fragments falling from the walls or erosion from the drilling medium. They are significant because they can block the hole, contaminate cuttings, and affect the accuracy of density geophysical logs.
📌 Why is the split-tube barrel the preferred choice for coal?
As described in 3.1.6.1, its design—two longitudinal halves of pipe bound together by reinforced tape—allows for easy access to the core by simply cutting the tape. This provides a relatively intact, undisturbed sample compared to traditional barrel designs.