Acetylene

Airgas specifies 99.6% minimum purity for its Atomic Absorption acetylene, with 0.4% maximum air, 25 ppmv phosphine and 25 ppmv total sulfurs as upper limits. This grade serves analytical flames. Specify the actual grade, cylinder solvent and delivery arrangement separately when comparing it with an oxyfuel supply. Airgas, Acetylene—Pure Gases

Identity and useful property conventions

Acetylene (ethyne), C₂H₂, CAS 74-86-2, has a molar mass of about 26.04 g/mol. Air Liquide lists oxyfuel, analytical and chemical uses. Air Liquide, Gas Encyclopedia: Acetylene

Keep units and reference conditions with every value. A cylinder's internal water capacity in litres is not the volume of acetylene available at atmospheric conditions. Gas quantities expressed in standard cubic feet or cubic metres depend on their defined temperature and pressure. Air Liquide's converter, for example, labels its gas reference conditions as 1.013 bar and 15°C. Do not silently equate that volume with another supplier's “standard” or “normal” cubic metre. Air Liquide, liquid/gas volume converter.

Gauge pressure is measured relative to local atmospheric pressure; absolute pressure includes it. Record psig/barg or psia/bara explicitly. This engineering convention is essential when comparing cylinder contents, regulator ratings, and process instructions.

Why the cylinder contains solvent and porous mass

Acetylene is normally supplied dissolved in acetone or dimethylformamide (DMF) within a specially designed cylinder containing porous filler. The solvent and porous structure allow storage under conditions that differ fundamentally from free acetylene in an empty pressure vessel. Air Products explains that the filler limits voids where free gas could collect. Its filling parameters depend on the cylinder construction. Air Products, Safetygram 13: Acetylene, cylinder construction.

Linde instructs users to let transported acetylene cylinders settle upright so solvent returns to the correct location in the mass. The necessary handling and settling instructions belong to the actual supply package; do not invent a universal waiting time. Solvent entering the delivered gas can affect process quality as well as equipment. Linde, Acetylene Fuel Gas, cylinder guidance.

Air Products prohibits user repairs and directs damaged cylinders back to the supplier. Treat shell, porous mass, solvent, and valve as one supplied package. Air Products, cylinder handling.

Oxyfuel roles and fuel-specific equipment

Acetylene supplies fuel in oxyacetylene welding, heating, brazing, and cutting processes. Linde describes its concentrated heating behavior and use with oxygen. This does not make oxygen and acetylene components interchangeable, nor does it make an acetylene installation a universal fuel-gas installation. Linde, acetylene applications.

Named hardware example: Smith's Little Torch manual OM-263357C, January 2017, lists several usable fuels but distinguishes tip compatibility. Its smallest tip is specified for acetylene or hydrogen; separate heating tips serve acetylene/hydrogen and propane/natural gas. The manual also distinguishes hose grades. A handle's broad fuel capability does not mean every fitted tip, hose, or regulator accepts every fuel. Follow the actual equipment's current instructions and fuel-specific pressure/flow chart. Miller/Smith, The Little Torch Owner's Manual, §§5 and 11.

Air Products requires equipment designed for acetylene service and warns that some metals can form sensitive acetylides. Select approved regulators, hoses, arrestors, valves, and piping materials as a system. Physical thread engagement is not evidence of gas-service compatibility. Air Products, ancillary equipment and materials selection.

Delivery rate and regulator limits are separate checks

The acetylene demand of a tip must be supported by the cylinder or approved manifold and by the regulator, hose, and safety devices. Air Products distinguishes intermittent and continuous withdrawal and explains that excessive draw can carry solvent into the gas, disturb the flame, and impair flashback-prevention equipment. Obtain permitted flow for the actual package and conditions. A memorized withdrawal fraction is not a complete supply design. Air Products, Safetygram 13, withdrawal guidance.

A pressure limit also is not a recommended operating setpoint. Miller's Smith gas-equipment hose table lists a 15 psig maximum regulator setting for acetylene service. That bounded table entry must be read with the hose and equipment specifications; it neither describes pressure inside a dissolved-acetylene cylinder nor determines the correct setting for an arbitrary torch. Use the selected tip's approved data and applicable local requirements. Miller, Accessories and Consumables Catalogue, Smith hoses and hose fittings, p. 92.

As engineering synthesis, excessive demand is resolved through supplier-approved capacity and equipment selection, not by exceeding a downstream pressure limit. Record both the required flow and its reference conditions before asking a supplier to size a package or manifold.

Grade and purity: buy against a specification

The Airgas catalog uses ppm by volume unless otherwise specified. Compare the named Atomic Absorption grade against the analytical method’s impurity, solvent and delivery limits. Airgas, Acetylene—Pure Gases

For an analytical burner, specify acceptable impurities and solvent carryover with the instrument manufacturer and gas supplier. For fabrication, confirm the process grade and package rather than assuming an analytical label improves every torch operation. Keep the gas specification, cylinder/solvent designation, connection, and any certificate requirement together. This selection guidance is engineering synthesis, not a claim that grades from different suppliers are equivalent.

SDS-backed storage and handling

The downloaded Airgas USA SDS 001001, version 5.05, revised March 28, 2025, identifies acetylene as an extremely flammable gas and describes the oxygen-depletion hazard. Its handling/storage sections call for adequate ventilation, control of ignition sources, upright secured cylinders with valve protection, and equipment rated for the cylinder pressure. It specifies that cylinder temperature must not exceed 52°C (125°F). These are instructions in that supplier's SDS, not a universal allowable workplace-temperature rule. Airgas, Acetylene SDS, §§2, 7–8.

The same SDS calls for closing the valve after use and when empty, and warns that containers can retain residues. Keep oxygen/oxidizer storage compatibility, leak response, and fire procedures tied to the current local SDS and site arrangements. A burning or heat-exposed cylinder requires emergency response; this reference is not a cylinder-recovery procedure. Airgas, SDS, §§5–7 and 13.

A useful supply record identifies supplier, grade, cylinder and solvent type, valve connection, compatible regulator and torch components, required flow/duty, source-specific limits, SDS revision, and jurisdiction. It supports repeatable selection without presenting a universal pressure recipe or jurisdiction-free regulatory claim.