Gas mixture uniformity testing service

Gas Mixture Uniformity Testing Service – Ensuring Compositional Consistency for Brazilian Oil, Gas and Industrial Applications

As an ISO/IEC 17025 accredited independent laboratory, we deliver specialised gas mixture uniformity testing services to Brazilian producers, importers, and process engineers. Whether you are handling natural gas from offshore pre‑salt fields, blending calibration standards for emissions monitoring, or verifying the homogeneity of industrial process gases, our analytical protocols confirm that every batch – from cylinder to pipeline – meets the required compositional consistency. Our methods are designed to satisfy the technical criteria of ANP (Brazil’s National Agency of Petroleum, Natural Gas and Biofuels), IBAMA (environmental licensing), and INMETRO for legal metrology, ensuring that your gas mixtures are defensible, traceable, and compliant with both Brazilian and international trade specifications.

Product Samples We Regularly Test for Uniformity

Our sampling and analytical capabilities cover a wide spectrum of gaseous matrices. Typical test specimens include:

• Natural gas streams – pipeline-quality gas, LNG regasification samples, and associated petroleum gas
• Liquefied petroleum gas (LPG) – propane, butane, and commercial LPG blends for heating and automotive use
• Calibration and reference gas mixtures – certified multi-component mixtures in high-pressure cylinders for CEMS, stack monitoring, and laboratory instrumentation
• Industrial process gases – synthesis gas (H₂/CO), nitrogen-hydrogen blends, oxygen-enriched air, and inert shielding gases for welding
• Specialty and medical gas mixtures – anaesthetic gas blends, respiratory therapy mixtures, and sterile gas combinations for pharmaceutical packaging
• Biogas and landfill gas – methane-carbon dioxide mixtures with trace siloxanes and sulfur compounds

Natural Gas and Fuel Gas Blends – Compositional Uniformity Verification

• Multi-point spot sampling from pipelines and vessels – We extract representative samples at multiple time points and locations (top, middle, bottom of storage spheres or along pipe runs) using stainless steel sample cylinders and regulated flow techniques. Sampling follows ISO 10715 (Natural gas – Sampling guidelines) to ensure that the collected aliquots truly reflect the bulk mixture at each point.
• Detailed hydrocarbon and inorganic component analysis – Each sample is analysed by gas chromatography with flame ionisation and thermal conductivity detection (GC-FID/TCD) according to ISO 6974 (Natural gas – Determination of composition). We quantify methane, ethane, propane, butanes, pentanes, hexanes, and higher hydrocarbons, along with nitrogen, carbon dioxide, oxygen, and helium. The resulting molar fractions are used to calculate key uniformity parameters.
• Uniformity index and statistical equivalence testing – We compare the composition across all sample locations using a Student’s t‑test and coefficient of variation (CV) for each component. A blend is considered homogeneous if the CV remains below a pre‑defined threshold (typically 2 % relative for major components and 5 % for minor ones) and if the measured composition lies within the allowable tolerance of the declared specification, as required by ANP Resolution No. 16/2021 for natural gas quality.
• Heating value and Wobbe index consistency – From the measured mole fractions, we calculate the superior calorific value (upper heating value) and Wobbe index using ISO 6976 (Natural gas – Calculation of calorific values, density, relative density and Wobbe indices from composition). Uniformity is confirmed when these energy-related parameters show a variation below 0.5 % across all sample sets, ensuring that combustion equipment receives a stable energy input.

Calibration Gas and Reference Mixtures – Gravimetric Preparation Verification & Batch Homogeneity

• Direct comparison of gravimetric vs. analytical concentration – For certified reference gas mixtures (CRM) prepared by gravimetric weighing, we perform independent verification using ISO 6142 (Gas analysis – Preparation of calibration gas mixtures – Gravimetric method) and ISO 6143 (Gas analysis – Comparison methods for determining and checking the composition of calibration gas mixtures). We weigh the full cylinder before and after filling, and then analyse the gas using a high‑precision GC system; the difference between the weighed composition and the measured composition must fall within the combined uncertainty budget (typically < 1 % relative).
• Intra‑cylinder and inter‑cylinder uniformity testing – For a single cylinder, we take aliquots from the cylinder valve with the cylinder in vertical and horizontal orientations to detect any stratification. For a batch of multiple cylinders (e.g., 10 % of a production lot), we analyse the first‑filled and last‑filled cylinders and at least two intermediate units, following ISO 6144 (Standard practice for preparation of calibration gas mixtures using dynamic volumetric methods) acceptance criteria. The measured mole fractions across cylinders must agree within the stated certification uncertainty.
• Stability and homogeneity over filling pressure – We perform pressure‑ramp sampling (at 150 bar, 100 bar, and 50 bar) on a single cylinder to verify that the mixture remains homogeneous as the cylinder is depleted. This is particularly critical for multi‑component mixtures containing heavy hydrocarbons or polar compounds (e.g., H₂S, NH₃) that may adsorb on internal surfaces; our testing follows ISO 10101 (Natural gas – Determination of water and methanol) recommendations for handling reactive trace compounds.
• Statistical control charts for production batches – We maintain process control charts (X̅ and R charts) for each component in routine production runs, applying ASTM D6299 (Statistical quality assurance) criteria to detect any drift or out‑of‑control condition, thereby assuring ongoing batch‑to‑batch uniformity.

Industrial Process and Specialty Gas Mixtures – In‑line and Cylinder Lot Uniformity

• On‑site process gas sampling with automated sample conditioning – For continuous process streams (e.g., synthesis gas loop, ammonia synthesis, ethylene oxide production), we use heated sample probes and fast‑loop systems to extract representative samples at the reactor outlet, intermediate stages, and final product line. The samples are analysed in real‑time using process GC or are collected in passivated cylinders for off‑line laboratory confirmation, with sampling intervals designed to cover one full production cycle (typically 8‑12 samples per shift).
• Total impurity and trace component profiling – We determine trace sulfur species (H₂S, COS, mercaptans) via ASTM D7493 (gas chromatography with sulfur chemiluminescence), oxygen using paramagnetic detection per ASTM D3985, and moisture using electrolytic or chilled‑mirror hygrometers (ISO 6327). Uniformity is assessed by comparing these trace levels across the sampling grid; a consistent low‐level profile confirms that the mixer or sparger is achieving effective macro‑ and micro‑mixing.
• Density and compressibility factor verification – For pure and mixed gases, we measure density using a vibrating tube densitometer per ASTM D4052 (adaptation for gases) and calculate the compressibility factor (Z) from measured pressure‑volume‑temperature data, comparing against AGA‑8 or GERG‑2008 equations. Uniformity is inferred when the calculated Z factor varies by less than 0.1 % across samples from the same batch – a critical check for custody transfer and fiscal metering.
• Leak integrity and headspace analysis for container homogeneity – For gas mixtures supplied in multiple cylinder bundles (e.g., for diving or medical use), we perform a leak check using helium mass spectrometry (ASTM E493) and then analyse the headspace after a defined equilibration period. This ensures that the mixture has reached full homogeneity within each cylinder and that no component has preferentially adsorbed onto the steel walls, particularly for reactive or high‑vapour‑pressure compounds.

Liquefied Petroleum Gas (LPG) and Volatile Hydrocarbon Mixtures – Phase Stability and Evaporation Uniformity

• Vapour‑phase vs. liquid‑phase composition comparison – We extract both liquid and vapour samples from a single LPG cylinder or storage bullet using specially designed dip tubes and vapour withdrawal valves. The compositions are determined by ASTM D2163 (GC analysis of LPG) and compared. Uniformity is confirmed when the ratio of each component in the vapour to that in the liquid matches the theoretical Raoult’s law predictions within the method’s precision, ensuring that the mixture will perform consistently during pressurised transfer and end‑use combustion.
• Batch evaporation curve and residue analysis – A full cylinder is gradually vaporised (e.g., 25 %, 50 %, 75 %, and 95 % of liquid mass withdrawn), and the composition of the vapour at each stage is analysed. The resulting evaporation profile is evaluated using the GPA 2177 method; a uniform mixture will exhibit less than a 5 % relative change in key components (e.g., propane/butane ratio) over the first 90 % of withdrawal, which is the typical performance requirement for Brazilian LPG supply contracts.
• Total sulfur and odorant uniformity – We also measure the concentration of odorants (typically ethyl mercaptan) using ASTM D6667 (GC with flame photometric detection) at multiple sample points to ensure that the odorisation level is uniform and meets ANP Resolution No. 19/2005 for leak warning purposes.

Report Acceptance & Compliance with Brazilian Regulatory Bodies

All uniformity tests described above are conducted within the framework of our ISO/IEC 17025:2017 accreditation, using reference materials traceable to NIST or other certified suppliers. Our final reports provide a clear summary of the sampling plan, analytical results per component, calculated uniformity statistics (CV, confidence intervals, and pass/fail criteria), and a comprehensive uncertainty budget (expanded uncertainty, k=2). We also include graphical representations (control charts, box plots, and evaporation curves) to facilitate rapid interpretation. These reports are directly acceptable to ANP for natural gas and LPG quality certification, to IBAMA for emissions monitoring reference gases, and to INMETRO for legal‑metrology verification of gas measuring instruments. We issue bilingual (Portuguese/English) versions to streamline your submissions to Brazilian authorities and internal quality review boards, ensuring that your gas mixtures are documented as homogeneous, fit‑for‑purpose, and compliant with all applicable regulatory standards.