DIN 51757 Testing of Mineral Oils and Related Materials - Determination of Density

The standard “DIN 51757 Testing of mineral oils and related materials - Determination of density,” published by the German Institute for Standardization (DIN), describes procedures for determining the density of mineral oils, petroleum products, crude oil, fuels, lubricants, and similar materials. For many years, this standard has been an important reference in the oil and petrochemical industry for quality control, product specification, and commercial purposes.

This standard defines several methods for measuring the density (kg/m³) of liquid mineral oil products and related substances. It is used particularly in the following areas:

• Crude oil and oil fractions
• Fuel oils (light and heavy)
• Lubricants
• Paraffins and similar materials

This standard includes the following procedures:

• Taking measurements at test temperature.
• Converting the measured density to a reference temperature of 15 degrees (very common in the oil industry)
• Convert the 15-degree density to other units if necessary (e.g., American Petroleum Institute (API) density in some contexts, but proprietary API standards also exist).

This standard defines various techniques, generally grouped as follows:

• Method A Hydrometer method (areometer): The classic, manual method using a glass hydrometer inside a cylinder (similar to ASTM D1298 and ISO 3675 standards).
• Method B Pycnometer method: A high-precision method using a pycnometer (a high-volume glass bottle) for calibration and measurement.
• Other/older variants: For example, hydrostatic balance or other density measuring devices (more options are described in some versions).

This standard includes temperature correction/conversion tables (particularly important since the density of hydrocarbons changes significantly with temperature).

Many technical data sheets for fuel oils, solvents, or lubricants list the density according to DIN 51757 at 20 degrees or 15 degrees, with values ​​such as 820-860 kg/m3 for diesel-like products or at least 1000 kg/m3 for heavy fuels.

The DIN 51757 standard has long been used in parallel with or as a national reference for the following standards:

• ISO 3675 Crude oil and liquid petroleum products - Laboratory density determination - Hydrometer method
• ISO 12185 Crude oil and petroleum products - Density determination - Oscillating U-tube method (currently the most common modern laboratory method)
• ASTM D1298 Hydrometer method for the density, relative density (specific gravity), or API density of crude oil and liquid petroleum products.
• The ASTM D4052 digital density meter is used to measure the density, relative density, and API density of liquids.

Many laboratories today use auto-oscillating U-tube densitometers, claiming compliance with both DIN 51757 and ISO/ASTM equivalents.

Several practical implications of this standard are listed below:

• Quality control in refineries, fuel terminals and blending processes.
• Commercial specifications and commercial registration of petroleum products.
• Research and development of fuels and lubricants.
• Frequently referenced in product certifications, safety data sheets, and marine fuel documents.

Although new oscillating U-tube methods have largely replaced manual hydrometers in modern laboratories due to their speed and accuracy, the DIN 51757 standard continues to be used as a reference in many specifications.

In short, DIN 51757 includes methods for determining the chlorine content in solid fuels such as bituminous coal, lignite (brown coal), coke, and related fuel materials. Chlorine is an important parameter in fuel analysis because even small amounts can lead to corrosion, environmental emissions, and operational problems in combustion systems.

This standard was developed within the scope of the DIN 51700 series of standards, which focuses on the analytical testing of solid fuels. The main objectives of this standard are as follows:

• To quantitatively determine the total chlorine content.
• To provide a reproducible laboratory method.
• To support environmental compatibility.
• To help assess the risk of corrosion in boilers and power plants.

Chlorine in fuel can form hydrogen chloride during combustion, which can lead to:

• It can cause corrosion in heat exchangers.
• It can cause damage to flue gas systems.
• It can increase maintenance costs.
• It can contribute to acid gas emissions.

The DIN 51757 standard applies to the following:

• hard coal
• Lignite
• Kok
• Briquettes
• Other solid fossil fuels

Meanwhile, the DIN 51757 standard is mainly used in the following areas:

• Power plants
• Industrial combustion plants
• Fuel testing laboratories
• Research institutions

The method described generally follows these steps:

• Sample preparation
• Drying and grinding of the fuel sample.
• Homogenization
• Combustion or decomposition
• The sample is either incinerated in an oxygen atmosphere or decomposed under controlled conditions.
• Chlorine is converted into hydrogen chloride or chloride ions.
• Absorption
• Combustion gases are absorbed in a suitable solution (usually water or an alkaline solution).
• Determination: Chloride concentration is measured using the following methods:
• Titration (e.g., silver nitrate method)
• Ion-selective electrode
• Ion chromatography (in modern adaptations)

The equipment commonly used in tests includes the following:

• Combustion furnace (high temperature)
• Oxygen supply system
• Absorption vessel
• Analytical balance (high precision)
• Titration apparatus or ion analyzer

The DIN 51757 standard defines the following in terms of accuracy and precision:

• Limits of repeatability
• Limitations of reproducibility
• Required sample size
• Calibration procedures

These ensure that results from different laboratories remain comparable.

Chlorine determination is of critical importance for the following reasons:

• Corrosion control: High chlorine levels accelerate corrosion in the following:
• Boilers:
• Superheaters
• Flue gas ducts
• Environmental compatibility: Chlorine contributes to:
• Hydrogen chloride emissions
• Formation of dioxins and furans under specific conditions.
• Economic impact: Accurate chlorine measurement helps to:
• Optimizing fuel selection
• Reducing maintenance costs
• To prevent unplanned shutdowns.

Although many laboratories now use automated analyzers and ion chromatography, the DIN 51757 standard retains its importance for the following reasons:

• Reference method
• Legal or contractual specification
• A benchmark for validating new techniques.

In conclusion, the DIN 51757 standard plays a critical role in solid fuel analysis by providing a standardized and reliable method for determining chlorine content. Its application helps industries control corrosion, comply with environmental regulations, and ensure fuel quality.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the DIN 51757 standard.