Gravimetric Fundamentals Weldcoa PowerPoint - 2023H2.pdf

10/2/2023 Topic: Gravimetric Filling Fundamentals 1 Gravimetric Filling Fundamentals Introductions Safety/Emergen...

10/2/2023 Topic: Gravimetric Filling Fundamentals 1 Gravimetric Filling Fundamentals Introductions Safety/Emergency/Telephone Procedures Gravimetric Filling Course Objective Schedule (Breaks, Lunches, Discussion, Lab, Plant Tour) © Copyright 2023 Welding Company of America All rights reserved. 2 Gravimetric Filling Fundamentals Agenda Cylinder selection & Cylinder preparation Safety precautions & OSHA/DOT/FDA Mixture Issues Temperature/Pressure vs. Gravimetric fill techniques Homogenization techniques Accuracy vs. Precision Gravimetric system uncertainty and sources Mixture calculations (Manual and automated methods) Pre-fill inspection & Mixture Process Management Post-fill calculations PPM-level mixtures using Base-Mix dilution technique Mixture confirmation – Policy Introduction to Fuel-Oxidant mixtures © Copyright 2023 Welding Company of America All rights reserved. 3 1  10/2/2023 Gravimetric Filling Fundamentals Mixture Issues – Cylinder Selection Appearance Material of construction Valve outlet connection See CGA V-7 (V-7.1 for medical) to determine the appropriate outlet connection for each mixture. Alternates exist for many mixtures Requalification date Prior gas service CGA C-10 / M-18 for change of service guidelines Cylinder Preparation & Passivation © Copyright 2023 Welding Company of America All rights reserved. 4 Gravimetric Filling Fundamentals Mixture Issues – Cylinder Preparation Pure and mixed gas cylinders must be leak-free & dry (0.5 to 7 ppm moisture) New* cylinders, use 135-140°F & 3 vacuum-purges. The vacuum levels should be at least 1 Torr (1.333 mbar) * new / re-hydrotested / valve is open To measure if this level can be achieved, use a good vacuum gauge like the Teledyne DV-6 / VT-6 meter The purge gas can be Nitrogen for the first two cycles, but it is recommended that the final purge gas be the product (or mix major component if not Nitrogen). © Copyright 2023 Welding Company of America All rights reserved. 5 Gravimetric Filling Fundamentals Vacuum Bake-Out Ovens © Copyright 2023 2021 Welding Company of America All rights reserved. 6 2  10/2/2023 Gravimetric Filling Fundamentals Millitorr (micron) vacuum gauge Teledyne VT-6 meter/DV-6 or KJL equivalent © ©Copyright Copyright 2023 2021Welding Welding Company Compay of ofAmerica America All All rights rights reserved. reserved. 7 Gravimetric Filling Fundamentals Mixture Issues – DOT Regulations Stable – no reactions … CO and steel – 5/6 rule 49CFR 173.302a Hydrotest rules, 10% overfill Shipping rules, labels, UN Numbers State rules (CA Proposition 65) © Copyright 2023 Welding Company of America All rights reserved. 8 Gravimetric Filling Fundamentals Mixture Issues – Stability Reactions with the cylinder wall Steel Aluminum Moisture CO2/CO : H2O 7 ppm max. in steel per CGA P-57 H2S Oxygen Nitric Oxide Shelf life Gases remaining homogenous © Copyright 2023 Welding Company of America All rights reserved. 9 3  10/2/2023 Gravimetric Filling Fundamentals Mixture Issues – Vapor Pressures Reliable mixture for the customer Homogenous Gas phase Some gases will liquefy if pressurized Carbon Dioxide, Nitrous Oxide, Hydrocarbons, SO2, etc. Stay away from the vapor pressure in order to avoid liquefaction 70% of VP at 70o F for typical specialty mixtures 85% of VP at 70o F for typical industrial mixtures 85% of VP at 32o F for components with < 150 psi VP © Copyright 2023 Welding Company of America All rights reserved. 10 Gravimetric Filling Fundamentals Mixture Issues – Vapor Pressures For example: CO2 VP = 845 psia (70% Limit = 592 psia) Using 3AA 2400 rated for +10% 10% CO2/Ar – 2640 psi (allowable top pressure) 20% CO2/Ar – 2640 psi 30% CO2/Ar – 1956 psi 40% CO2/Ar – 1464 psi 50% CO2/Ar – 1168 psi © Copyright 2023 Welding Company of America All rights reserved. 11 Gravimetric Filling Fundamentals Mixture Issues – Stress Corrosion Cracking Trans-granular Cracks in a Branching Pattern © Copyright 2023 Welding Company of America All rights reserved. 12 4  10/2/2023 Gravimetric Filling Fundamentals Mixture Issues – SCC The mechanism is understood to be local dissolution of iron due to the carbonic acid formed between water and carbon dioxide, with general corrosion being inhibited by carbon monoxide. This phenomenon leads normally to trans-granular cracks with branching. This phenomenon has nothing to do with hydrogen embrittlement, which normally leads to intergranular cracks. © Copyright 2023 Welding Company of America All rights reserved. 13 Gravimetric Filling Fundamentals Mixture Issues – SCC 4 factors must be present for stress corrosion cracking (SCC) to occur, per CGA P-57 specifically: > 5ppm Carbon Monoxide must be present. > 5ppm Carbon Dioxide must be present. Liquid water must be present. Carbon steel under stress (defined as: >1,000 psig).  High-strength steel cylinders, ISO 9809-2, shall not be used.  Moisture when in CO2/CO : H2O < 7 ppm  Sulfur-free per 49CFR 302a(c) © Copyright 2023 Welding Company of America All rights reserved. 14 Gravimetric Filling Fundamentals Mixture Issues – SCC-prone example mixes Laser Gas Mixtures These can have carbon monoxide concentrations up to 4% and carbon dioxide concentrations of 8% or higher. Air quality (emissions) mixtures These may routinely contain high concentrations (up to 20% or more) of both carbon monoxide and carbon dioxide depending on the emission being monitored. Modified Atmosphere Packaging These are applications in the food industry (e.g., Praxair Extendapak-78) contains carbon monoxide at 0.4% and carbon dioxide at 30%. © Copyright 2023 Welding Company of America All rights reserved. 15 5  10/2/2023 Gravimetric Filling Fundamentals Oxygen Safety Swagelok MS-06-13 (handout) Solvents vs Cleaners (aqueous-based) Inspection & Documentation Proper storage if not placed in service immediately © Copyright 2023 Welding Company of America All rights reserved. 16 Gravimetric Filling Fundamentals Periodic Maintenance Hoses (handout) Gaskets O-rings Viton vs. Buna-N for CO2 Swing-arm Threaded fittings Adaptors © Copyright 2023 Welding Company of America All rights reserved. 17 Gravimetric Filling Fundamentals Periodic Maintenance Also, consider how they are stored © Copyright 2023 Welding Company of America All rights reserved. 18 6  10/2/2023 Gravimetric Filling Fundamentals Mixture Issues – Safety The chemical compatibility of acid or basic gases with a fuel or oxidizing gas will be determined in writing before the mixture is made. The chemical compatibility of carbon monoxide with corrosive or sulfur containing gases will be determined in writing before the mixture is made. The partial pressure of acetylene in a mixture will not exceed 22 psia. © Copyright 2023 Welding Company of America All rights reserved. 19 Gravimetric Filling Fundamentals Mixture Issues – Safety The chemical compatibility of hydrogen sulfide and sulfur dioxide containing gases will be determined in writing before the mixture is made. The chemical compatibility of hydrogen and unsaturated hydrocarbons (ethylene, acetylene, propylene, etc.) will be determined in writing before the mixture is made. Mixtures containing both acid and basic gases will not be made, (e.g., Carbon dioxide & Ammonia). © Copyright 2023 Welding Company of America All rights reserved. 20 Gravimetric Filling Fundamentals Technology – Homogenization Roller © Copyright 2023 Welding Company of America All rights reserved. 21 7  10/2/2023 Gravimetric Filling Fundamentals Technology – Homogenization Inverter Some mixtures can be made so they are mostly homogenous as soon as they are filled (N2/O2) Order of addition Dip/Eductor/ Syphon tubes (not recommended for SG blends) © Copyright 2023 Welding Company of America All rights reserved. 22 Gravimetric Filling Fundamentals Technology – Pressure/Temperature Gauges, thermometer and pressure/ temperature charts © Copyright 2023 Welding Company of America All rights reserved. 23 Gravimetric Filling Fundamentals Technology – Press./Temp. NBS Technical Note 1079, Tables of Industrial Gas Container Contents and Density for Oxygen, Argon, Nitrogen, Helium and Hydrogen (1985) 50% Helium in Argon Ideal gas – 1320 psi He; 2640 psi Ar Real gas – 1392 psi He; 2640 psi Ar 50% Xenon in Argon Ideal gas – 1320 psi Xe; 2640 psi Ar Real gas – 643 psi Xe; 2640 psi Ar Equations of State --- all estimates Ideal Gas Law: PV=nRT - Clapeyron (1834) van der Waals equation of state (1873) Redlick-Kwong equation of state (1949) Peng-Robinson equation of state (1976) © Copyright 2023 Welding Company of America All rights reserved. 24 8  10/2/2023 Gravimetric Filling Fundamentals Molar Gas Constant: R=pV/nT R (Gas Constant*) = 8.31446261815324 J.K-1. mol-1 = 0.0820573660809596 L. atm. K-1. mol-1 = 1.205911 L. psi. K-1. mol-1 T = 70°F = 21.1°C + 273.15 = 294.2611 K RT = 354.8527 L. psi. mol-1 *20 May 2019: Equal to the product of two of the SI defining constants, the Boltzmann constant and the Avogadro constant. © Copyright 2023 Welding Company of America All rights reserved. 25 Gravimetric Filling Fundamentals Technology – Gravimetric Scale High sensitivity scale High integrity control system © Copyright 2023 Welding Company of America All rights reserved. 26 Gravimetric Filling Fundamentals Technology – Gravimetric Scale Based on the mass of individual gas components – grams Largely independent of equation of state estimates Much higher accuracy and precision Can be better than other instrumentation … Or can be worse … depends on system “uncertainty” © Copyright 2023 Welding Company of America All rights reserved. 27 9  10/2/2023 Gravimetric Filling Fundamentals Blend Tolerance Example Mixture Preparation Tolerance is the variation of a component from the requested concentration © Copyright 2023 Welding Company of America All rights reserved. 28 Gravimetric Filling Fundamentals What is an “analytical result?” Measurand – The measurand is the product instrument reading and includes the units being measured. The measurand is typically declared as the analytical result. (e.g., Nitrogen 7 μmol/mol (ppm) in Argon. This is only one of three parts to a proper declaration of a result. © Copyright 2023 Welding Company of America All rights reserved. 29 Gravimetric Filling Fundamentals What is “uncertainty?” Uncertainty - All analytical measurements have some uncertainty around the reading. This principle is true for gas chromatographs, thermometers, gravimetric scales, trace moistures analyzers, etc. Uncertainty is usually expressed in relative terms (e.g., +/- 1 % relative). For example, a measurand with uncertainty might be declared: 7 µmol/mol +/- 5 % relative. “Rel.” may substitute for “Relative” and is assumed if not otherwise specified. © Copyright 2023 Welding Company of America All rights reserved. 30 10  10/2/2023 Gravimetric Filling Fundamentals Uncertainty versus Error Uncertainty - is a quantification of the doubt about the measurement result. Accuracy Error (or Bias) is the difference between the measured value and the ‘true value’ of the thing being measured. © Copyright 2023 Welding Company of America All rights reserved. 31 Gravimetric Filling Fundamentals What is “Confidence Interval?” Confidence Interval – when we declare the measured reading along with the measurement uncertainty, we must include a statement of the confidence we have that the true reading is within the stated uncertainty. This is typically done with a confidence interval statement. The following confidence interval statements are approximately equivalent: “95 % confidence interval”, “95 % CI” and k=2. All these statements indicate that the true reading will be within the stated uncertainty approximately 95 % of the time (two standard deviations). © Copyright 2023 Welding Company of America All rights reserved. 32 Gravimetric Filling Fundamentals Confidence Interval 5% CO2 ± 0.05% abs (95% CI)… We are not saying that the reading will absolutely (100% of the time, guaranteed) be 5% ± 0.05%. We are saying that 95% of the time the true reading will be within 0.05% Statistically, it is not possible to guarantee 100% of the readings will be in specification (±0.05%) Consider the tail of the bell curve extends infinitely. © Copyright 2023 Welding Company of America All rights reserved. 33 11  10/2/2023 Gravimetric Filling Fundamentals © Copyright 2023 Welding Company of America All rights reserved. 34 Gravimetric Filling Fundamentals Relative versus Absolute 5% CO2 ± 0.05% abs (95% CI)… If your analytical result is 5.00% Carbon Dioxide, ± 1% relative (95% CI), then the uncertainty is ±1% relative of 5% or ±0.05% absolute © Copyright 2023 Welding Company of America All rights reserved. 35 Gravimetric Filling Fundamentals Declaring an analytical result These would be typical and equivalent analytical results: 5.00% Carbon Dioxide (± 1% rel., 95% confidence interval) 5.00% Carbon Dioxide (± 1% relative, k=2) 5.00% Carbon Dioxide (± 0.05% absolute, CI= 95%) © Copyright 2023 Welding Company of America All rights reserved. 36 12  10/2/2023 Gravimetric Filling Fundamentals Uncertainty Sources Operator bias (not “blunders”) Loose fittings - Leaks Accuracy (Calibration and Linearity) Source gas purity (O2, CO2, Propane…) Air currents Drift over time Precision (scale, and fill-line or “pigtail”) Scale Resolution (smallest increment on display) © Copyright 2023 Welding Company of America All rights reserved. 37 Gravimetric Filling Fundamentals Type A Uncertainty Sources Describing a population Assumed normally distributed Uncertainty (u) = √ [∑ (xi – μ)2 / (n * (n – 1))] Or in Excel =STDEV.S(range of readings)/SQRT(n) For all combined standard uncertainty sources, we propagate using RSS and apply k=2 to get expanded uncertainty © Copyright 2023 Welding Company of America All rights reserved. 38 Gravimetric Filling Fundamentals Type B evaluation (characteristic) Uniform (rectangular) Distribution © Copyright 2023 Welding Company of America All rights reserved. 39 13  10/2/2023 Gravimetric Filling Fundamentals Operator Bias Use care that you do not wait for the “correct” or desired mass to appear when taking your measurements. For example, try to take your measurements at a certain number of seconds after the application of the weight. This helps to minimize operator bias in recording the measurements. © Copyright 2023 Welding Company of America All rights reserved. 40 Gravimetric Filling Fundamentals Calculation of uncertainty ISO 6142:2001/ Amd.1:2009(E) described a standard method to calculate the uncertainty performance on a gravimetric fill system. Includes at least seven major uncertainty elements Pooled uncertainty Weights Buoyancy Residual gas Purity of gases Molar masses “Other” sources © Copyright 2023 Welding Company of America All rights reserved. 41 Gravimetric Filling Fundamentals Calculation of uncertainty Or a simplified approach… Type A evaluation Estimate by repeated measurements Population (e.g., n=5 weighings) Type B evaluation Realistic estimate of contribution Characteristic (e.g., scale display resolution) © Copyright 2023 Welding Company of America All rights reserved. 42 14  10/2/2023 Gravimetric Filling Fundamentals Uncertainty Analysis - Scale Quick scale uncertainty estimation 1. Using the 150 Kg scale, place a large cylinder on the scale 2. Select a weight or cap – approximately 1000 grams 3. Tare the scale 4. Place the weight on the scale, record the indicated value. 5. Remove the weight. 6. Allow the display to zero. Press Tare as needed. 7. Repeat the steps 4 and 5 above four more times (n=5). 8. Calculate the standard deviation of the readings. 9. Calculate the standard uncertainty: u = Standard deviation / n0.5 or Excel: u=STDEV(X1:X5)/SQRT(5) © Copyright 2023 Welding Company of America All rights reserved. 43 Gravimetric Filling Fundamentals Uncertainty Analysis – Fill Lead Fill Lead or “Pigtail” uncertainty estimation Calculate the torque/mass/volume in the pigtail and fill line Place a cylinder on the scale and connect to the fill pigtail Keep the cylinder valve closed Tare the scale Pressurize the pigtail with Nitrogen to approximately 2100 psig Slowly Read and record the scale weight Repeat the test four more times using the previous pressure achieved (5 total) Calculate the standard deviation and standard uncertainty © Copyright 2023 Welding Company of America All rights reserved. 44 Gravimetric Filling Fundamentals Uncertainty Analysis – Fill Lead Acceptance Criteria: A ¼ inch SS pigtail should read ~3.0 grams. A 1/8-inch pigtail should read ~1.5 grams. This number should be very repeatable. We have seen over a 400-gram (non repeatable) deflection with ¼ inch Teflon lined hoses. © Copyright 2023 Welding Company of America All rights reserved. 45 15  10/2/2023 Gravimetric Filling Fundamentals Uncertainty Analysis – Display The third element of the quick estimation is the resolution or smallest digit seen on the scale display. This is quantified as standard uncertainty by dividing it by the square root of 3. When all three standard uncertainties are combined and a coverage factor (k=2) is applied, the combined expanded uncertainty is estimated. © Copyright 2023 Welding Company of America All rights reserved. 46 Gravimetric Filling Fundamentals Calculate Minimum Masses Estimate the gravimetric standard uncertainty (in grams) from all sources (scale, pigtail torque, purity of the gases, drift, air currents, etc.) Combine using the “Root Sum Square” method. Multiply the standard deviation by two. This is an estimate of the uncertainty of the scale. 95% of the scale readings are within +/- these grams. Divide this estimated scale uncertainty by the certification accuracy for the mixture. © Copyright 2023 Welding Company of America All rights reserved. 47 Gravimetric Filling Fundamentals Calculate Minimum Masses Example: Let’s assume that the total uncertainty for a Sartorius 150 Kg x 0.1 balance is 0.5 grams and that we want to make a Primary Standard mixture with 1% certification accuracy. Divide the 0.5 grams by 1% ….. (0.5 / 0.01 = 50 grams) The boundary of the 1% tolerance is 50 grams. This assumes no other uncertainty/errors. It is recommended to use a buffer of 1.5 to 2x © Copyright 2023 Welding Company of America All rights reserved. 48 16  10/2/2023 Gravimetric Filling Fundamentals Mixture Process Management CGA P-36 Principle 1: written instructions shall be provided Principle 2: equipment and facilities shall be properly designed Principle 3: written instructions shall be prepared by competent staff using recognized data Principle 4: personnel shall be trained Principle 5: intended cylinder content shall be identified before filling Principle 6: supply gases and cylinders shall be controlled Principle 7: facilities and procedures shall be audited © Copyright 2023 Welding Company of America All rights reserved. 49 Gravimetric Filling Fundamentals Mixture Process Management CGA P-36 Principle 1: Written instructions shall be provided Pre-approved Plant and equipment operating procedures Order of addition, base mixes, etc. Each gas mixture © Copyright 2023 Welding Company of America All rights reserved. 50 Gravimetric Filling Fundamentals Mixture Process Management Principle 2: Equipment and facilities shall be properly designed · Pressure and material compatibility · Formally approved · Segregation of flammables and oxidizers, etc. · Prevention of cross contamination · Environmentally responsible and safe disposal of waste gases (see P-63) © Copyright 2023 Welding Company of America All rights reserved. 51 17  10/2/2023 Gravimetric Filling Fundamentals Mixture Process Management Principle 3: Written instructions shall be prepared by competent staff using recognized data · Check for availability of recognized data · Fill method safety (and viability) · Vapor pressure / condensation issues · Over/underfilling (size “C” vs. “C”) · Tolerance requirements © Copyright 2023 Welding Company of America All rights reserved. 52 Gravimetric Filling Fundamentals Mixture Process Management Principle 4: Personnel shall be trained · All aspects of filling mixtures (pre-fill to painting/labeling) · SDSs: Gas hazards & safety requirements · Recognition and mitigation of the hazards during mixture preparation that is found to be unsafe · PPE · Emergency SOPs, First Aid · Documented and updated regularly, and competency assessed and confirmed © Copyright 2023 Welding Company of America All rights reserved. 53 Gravimetric Filling Fundamentals Mixture Process Management Principle 5: Intended cylinder content shall be identified before filling · Label (at least temporary) before filling · Which gases · Nominal concentrations · Status (Vacuum, full, rolled…) recorded © Copyright 2023 Welding Company of America All rights reserved. 54 18  10/2/2023 Gravimetric Filling Fundamentals Mixture Process Management Principle 6: Supply gases and cylinders shall be controlled Only use intended gases (Argon vs Oxygen) · and grades USP vs. UHP Cylinders must be properly prepared · especially customer-owned cylinders Contamination free © Copyright 2023 Welding Company of America All rights reserved. 55 Gravimetric Filling Fundamentals Mixture Process Management Principle 7: Facilities and procedures shall be audited All operational gas mixing facilities and procedures shall be audited regularly for compliance with the previous six principles · Pre-approved expectations (acceptance) · Periodic audits for compliance to above · Technical and management participation © Copyright 2023 Welding Company of America All rights reserved. 56 Gravimetric Filling Fundamentals Prefill Inspection CGA C-6 Standards for Visual Inspection of Steel Compressed Gas Cylinders CGA C-6.1 Standards for Visual Inspection of High-Pressure Aluminum Compressed Gas Cylinders © Copyright 2023 Welding Company of America All rights reserved. 57 19  10/2/2023 Gravimetric Filling Fundamentals Prefill Inspection OWNERSHIP 49 CFR 173.301(e) VALVE PROTECTION CAPS / NECK THREADS TEST DATES, DOT MARKINGS (Serial Number, Rating, Star, Plus, etc.) SURFACE DAMAGE Dent - Any dent on cylinder sidewall Cut, gouge or dig - Any cut, gouge or dig on cylinder sidewall Rust or pits - Line corrosion Bulge - Any bulge on cylinder is over 1/16 in. high. Arc Burn - Cylinder has an arc burn or a torch burn, no matter how small. © Copyright 2023 Welding Company of America All rights reserved. 58 Gravimetric Filling Fundamentals Prefill Inspection UNSTABLE BOTTOM (no leaning) FIRE CYLINDERS (Steel: paint burned away; Aluminum: >350°F) CONTAMINATION Hydrocarbon based contamination, biological contamination VALVE INSPECTION Inspect the Pressure Relief Device (safety)