5 Analytical Instrumentation Precision without compromise


Every standardized test method must include an evaluation of its precision. The D7042 standard provides a comprehensive performance assessment, entirely conducted by ASTM, across a wide range of sample types and temperatures relevant to the petroleum industry. These samples include base oils, formulated oils, diesel and biodiesel fuels, jet fuels, and residual fuel oils. During the development of the method, multiple laboratories worldwide measured several samples of each type using both the D7042 and the D445 method for comparison. For each sample type, a detailed research report was published, outlining the precision of both methods. Table 1 lists examples extracted from these reports.


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standard dynamic viscosity and density measurements, it can determine a wide range of derived parameters, all fully compliant with ASTM standards. For example, the method offers the fl exibility to simultaneously measure viscosity at both 40 °C and 100 °C. According to ASTM D2270,3


these


values can then be used to calculate the viscosity index (VI). Another feature of D7042-compliant instruments is the determination of the viscosity gravity constant (VCG) in accordance with ASTM D2501,4 (M) following ASTM D2502,5 results as input values.


Table 1: Precision of D7042 vs D445


Base Oils at 40 °C8 Instrument


or the mean molecular mass both of which accept D7042


Moreover, using these parameters alongside refractive index measurements, D7042 viscometers can calculate the carbon type composition (CTC) in compliance with ASTM D2140,6


determine the carbon distribution and ring content according to ASTM D3238.7


These built-in calculation capabilities


signifi cantly enhance the practical applicability of D7042 viscometers, offering a more comprehensive analysis in a single, automated process.


Unmatched simplicity


ASTM D7042 is designed to accommodate a wide range of sample introduction methods, from manual handling to fully automated systems, which may even include pre-heating capabilities. The latest iteration of D7042 viscometers has taken sample introduction to the next level of simplicity. These instruments are equipped with a funnel, allowing the operator to directly pour the sample into the device – eliminating the need to transfer the sample into a vial, using a pipette or syringe beforehand. With just the push of a button, the sample is automatically fi lled, measured in full compliance with D7042, and drained, all without requiring any further user intervention.


Repeatability r(95) Reproducibility R(95) Jet fuels at -20 °C9 Instrument


Repeatability r(95)* D7042 D445


Anton Paar SVM Glass capillary 0.09 % 0.58 % D7042


0.25 % 0.79 % D445


Anton Paar SVM Glass capillary 1.07 %


or


Reproducibility R(95)* 1.86 % Formulated oils at 40 °C10 Instrument


Repeatability r(95)** /s


Reproducibility R(95)** 1.16 % * at 7.98 mm2 ** at 150.7 mm2


/s


In a nutshell, in all of the listed studies, the performance of D7042 was found to be equal or even better than the same sample set measured in accordance to D445.


Studies conducted by ASTM have also provided statistical insights into potential systematic deviations, or biases, between test methods D445 and D7042. Such biases have been identifi ed for certain sample types and temperatures. Conveniently, the statistical analysis yielded formulas that allow users to convert D7042 results to D445, producing values that can be considered practically equivalent to those from the traditional method.


These bias formulas are integrated into D7042-compliant viscometers, enabling automatic calculations and removing the need for users to perform manual conversions. This built-in functionality streamlines the process, making it easier for operators to obtain results that correspond reliably to D445 measurements.


Versatility in key specifi cations


In the past 20 years of its existence, ASTM D7042 has become an established test method widely recognized across critical petroleum specifi cations, including D97511 for distillate and diesel fuels, SAE J30013 lubricants, ASTM D39615


and EN 59012 and D607414 for fuel oils, D615816 for hydraulic oils, and D369918


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Maximum fl exibility


The measurement principle outlined in ASTM D7042 offers remarkable fl exibility. Its integrated thermoelectric temperature control, coupled with compact low-volume measuring cells, enables instruments to achieve rapid and automatic thermal equilibration of the sample as well as heating and cooling rates of up to 20 °C per minute. Together, these features provide signifi cant advantages over the conventional glass capillary method by enabling a broader range of sample analysis, from jet fuel


(-40 °C) to wax (+135 °C) in one instrument. Fully automated temperature scans can be performed to study the temperature dependence of samples. Additionally, unlike the glass capillary method, which measures viscosity at discrete points, the continuous nature of the viscosity measurement in ASTM D7042 allows for real-time monitoring of viscosity changes over time via a time scan.


for and D802917 for kerosene, among others.


In the aviation industry, the method is also fully compatible with standards like ASTM D165519 ASTM D756620


for aviation fuels containing synthesized hydrocarbons, as well as JIG AFQRJOS21 and Def Stan 91-091.22


As mentioned, one of the key advantages of the D7042 method is its dual capability to measure both viscosity and density, making it exceptionally versatile. This dual functionality aligns with specifi cations that require density as a parameter, enabling simultaneous certifi cation of both viscosity and density. For modern instruments, this versatility extends to full compliance with ASTM D4052,23


further enhancing their applicability across the latest petroleum industry standards. Reduced maintenance


A key advantage of the D7042 measurement principle is its single measuring cell, which spans the entire viscosity range. This eliminates the need for tracking multiple glass capillaries in a quality management (QM) system. Additionally, D7042 viscometers are factory-calibrated across a broad temperature and viscosity range. As with any analytical technique, adhering to good laboratory practices is essential. It is recommended that reference materials be periodically measured to ensure optimal instrument performance, a process commonly


SVM 1001 Simple Fill: Simply Kinematic Viscosity - No Syringe Needed References


1 ASTM D445-23, “Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calcula-tion of Dynamic Viscosity),” Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA.


2 ASTM D7042-21a, “Standard Test Method for Dynamic Viscosity and Density of Liquids by Stabinger Viscometer (and the Calculation of Kinematic Viscosity),” Annual Book of ASTM Standards, ASTM International, West Con- shohocken, PA.


WWW.PETRO-ONLINE.COM for aviation turbine fuels, D7042


1.24 % 2.18 % D445


Anton Paar SVM Glass capillary 0.64 %


1.07 % 1.90 %


referred to as calibration. This procedure does not alter the instrument’s constants. Adjustments to these constants are only necessary when signifi cant deviations from the reference material are detected. Such adjustments can be fully automated in modern instruments, ensuring ease of operation and accuracy.


In contrast, maintaining accuracy with glass capillary viscometers, as specifi ed by ASTM D445, is far more complex and requires frequent checks of both timing devices and bath thermometers as specifi ed by D445 at regular intervals. And although D445 does not regulate the frequency of viscosity tube calibration, many manufacturers of automated equipment indeed mandate recalibration, particularly when operating at a new temperature.


SVM 2001: Viscosity, Density, and More at a Range of Temperatures The future of viscosity testing is here


In conclusion, ASTM D7042 represents a signifi cant advancement in viscosity testing technology, offering a modern alternative to the traditional ASTM D445 glass capillary method. By directly measuring dynamic viscosity and density, D7042 provides an effi cient, accurate, and versatile approach for determining kinematic viscosity – addressing many of the operational limitations and resource demands of the D445 method. The automated D7042 technique simplifi es sample handling, reduces the required quantities of sample and solvent, and shortens temperature equilibration times, while covering the entire viscosity range with a single cell.


The D7042 standard is compliant with an extensive list of industry specifi cations and also offers enhanced multiparametric capabilities. In addition to providing density and viscosity information, D7042 viscometers can calculate additional values such as the viscosity index, molecular mass, and carbon type composition, adding depth to petroleum analysis. Furthermore, built-in ASTM bias formulas ensure that D7042 measurements are practically equivalent to D445, increasing confi dence in cross-method comparisons without manual calculations.


The precision and reliability of ASTM D7042, coupled with its reduced maintenance requirements, make it a valuable tool for quality control in the petroleum industry and beyond. This innovative approach aligns with modern demands for accuracy, sustainability, and operational effi ciency, providing industries with a contemporary solution for viscosity testing.


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