50 terms across 8 areas
Cylinders
- DA cylinder
- A dissolved-acetylene cylinder — acetylene dissolved in acetone or DMF held in a solid porous mass, rather than compressed as free gas.Free acetylene above about 1.5 bar can decompose violently, so it cannot simply be compressed. The porous mass and solvent are what make roughly 16 atmospheres safe to store and transport.Read more →
- Porous mass
- The solid, finely divided filler inside an acetylene cylinder that holds the solvent and divides the gas space into tiny cells.By breaking the interior into small cells it stops a decomposition reaction propagating through the cylinder. A degraded or shrunken mass is a reason to withdraw a cylinder from service.Read more →
- Tare weight
- The stamped empty weight of a cylinder, including — on a DA cylinder — the porous mass and the solvent charge.It is the reference for checking solvent content: actual empty weight against stamped tare tells the filling station how much acetone is missing.Read more →
- Water capacity
- The internal volume of a cylinder in litres, measured as the water it would hold — not the amount of gas it contains.A standard 47 L water-capacity cylinder charged to 150 kg/cm² holds about 6.87 Nm³ of a permanent gas.Read more →
- Cylinder bank
- Several cylinders manifolded together to draw as one supply, also called a quad or pack.Used where a single cylinder cannot sustain the flow, or where a changeover panel is needed so production never stops for a cylinder change.
- Siphon cylinder
- A cylinder fitted with an internal dip tube so it delivers liquid rather than gas.Used for CO₂ where liquid is required — dry ice production, some fire systems. Fitting a siphon cylinder to a gas application will not work and can be dangerous.
- 1/7 rule
- The limit on drawing acetylene from a DA cylinder: no more than one-seventh of its contents per hour.Exceeding it drags acetone solvent into the torch and starves the flame. It also protects the cylinder’s own solvent charge over its service life.Read more →
Standards
- IS 4379
- The Indian Standard for identifying the contents of industrial gas cylinders by ground colour and neck band.Referenced by the Gas Cylinder Rules. Note that medical cylinders follow IS 3933 instead, and that oxygen and CO₂ are both black — the white band distinguishes CO₂.Read more →
- IS 3933
- The Indian Standard for identifying medical gas cylinders — separate from the industrial IS 4379.Because the two standards differ, a medical cylinder’s contents must never be inferred from the industrial colour chart.
- PESO
- The Petroleum and Explosives Safety Organisation — the Indian authority that licenses and approves gas plant, cylinders and filling stations.PESO approval is a legal precondition for operating acetylene generation and cylinder filling in India, not a quality badge.
Units
- Nm³ (normal cubic metre)
- A cubic metre of gas measured at 0 °C and 1 atmosphere — a fixed quantity of gas, not a variable volume.The convention across India and Europe. One Nm³ occupies 1.055 m³ once warmed to 15 °C, which is why quoting plain "m³" without a basis causes disputes.Read more →
- SCF (standard cubic foot)
- A cubic foot of gas at US standard conditions, normally 60 °F and 1 atmosphere.One Nm³ = 37.35 SCF — not the 35.31 a plain volume conversion gives, because of the 0 °C to 60 °F correction. Missing this is a 5.8% billing error.Read more →
- Relative vapour density
- The density of a gas compared with air at the same conditions. Above 1.0 it sinks; below 1.0 it rises.This single number decides where a leak accumulates. Argon at 1.38 and CO₂ at 1.53 pool in pits and cellars; hydrogen at 0.07 gathers at roof level.Read more →
- vpm / ppm
- Volumes per million — the unit impurities are quoted in. One vpm is 0.0001%.A healthy acetylene purifier takes phosphine down to about 0.1 vpm, which is why purity alone (98.5%) does not tell you whether the gas is clean.
- Gauge vs absolute pressure
- Gauge pressure (kg/cm²g, barg) is measured above atmospheric; absolute includes atmospheric pressure.A cylinder gauge reads zero when the cylinder is at atmospheric pressure — it still contains a cylinder full of gas at 1 atm absolute.
Production
- PSA (pressure swing adsorption)
- A process that separates oxygen or nitrogen from air using a molecular sieve that adsorbs one component preferentially at pressure.Runs as twin towers swapping on a sub-minute cycle. Reaches 93–95% oxygen — the ceiling is set by argon, which the sieve does not separate well from oxygen.Read more →
- ASU (air separation unit)
- A cryogenic plant that liquefies air and distils it into oxygen, nitrogen and argon.Separation works because the three boil at different temperatures — nitrogen −195.8 °C, argon −185.8 °C, oxygen −183.0 °C. That ten-degree spread is the whole process.Read more →
- Carbide-to-water generation
- The wet method of making acetylene, feeding calcium carbide into a water-filled generator.Produces markedly cleaner gas than dry generation, because the alkaline lime slurry scrubs out ammonia and almost all sulphur as the gas forms.Read more →
- Carbide lime
- The calcium hydroxide slurry left over after calcium carbide has reacted with water.A by-product with genuine uses — soil treatment, effluent neutralisation, construction — rather than pure waste.Read more →
- Purifying mass
- The solid oxidising medium in an acetylene purifier that removes phosphine, arsine and sulphur compounds from generator gas.Typically ferric chloride with mercuric chloride and copper chloride on kieselguhr, capped with lime. Air-regenerable roughly ten times before disposal.Read more →
- Molecular sieve
- A crystalline adsorbent — usually a zeolite — with pores sized to trap specific molecules.Used in PSA separation, in acetylene purity trains to lift gas from 98.5% to 99.5%, and in ASU pre-purification to strip water, CO₂ and hydrocarbons.
- Space velocity
- The rate of gas flow through a bed relative to the bed volume, quoted per hour.It sets contact time. An acetylene purifier removes phosphine to 0.1 vpm at about 50 per hour, but is regenerated far more slowly at around 12 per hour.
Welding
- Shielding gas
- The gas that keeps atmospheric oxygen and nitrogen away from a molten weld pool until it solidifies.Without it the pool absorbs air, producing porosity, brittle nitrides and — on stainless — discolouration and lost corrosion resistance.Read more →
- Root purging
- Filling the inside of a pipe joint with argon so the back of the weld does not oxidise.Without it a stainless root oxidises into rough grey scale — "sugaring" — which destroys corrosion resistance exactly where the pipe carries product.Read more →
- Sugaring
- The rough grey oxide scale that forms on the underside of a stainless weld made without a back-purge.In food, pharmaceutical and chemical pipework a sugared root is a rejected weld, not a cosmetic defect.
- Flashback
- A flame travelling back through the torch into the hose, toward the cylinder.Distinct from a backfire, which is a momentary pop at the tip. Needs gas velocity to fall below flame speed plus a fuel-oxygen mixture upstream.Read more →
- Flashback arrestor
- A device that stops a flashback travelling further up the gas line and extinguishes it.Fitted at both regulator and torch, on both fuel and oxygen. An arrestor that has taken a flashback must be replaced, not reused.Read more →
- Non-return valve
- A one-way valve that prevents gas flowing backwards up a hose and creating a mixed fuel-oxygen charge.Works with the flashback arrestor rather than replacing it — the valve stops the reverse flow that feeds a flashback, the arrestor stops the flame.
- Neutral flame
- An oxy-acetylene flame with balanced fuel and oxygen, showing a clearly defined inner cone and no acetylene feather.The setting for most steel welding. Excess acetylene gives a carburising flame that adds carbon; excess oxygen gives an oxidising flame that burns the weld.
Applications
- MAP (modified atmosphere packaging)
- Replacing the air in a food pack with nitrogen, or nitrogen and CO₂, to extend shelf life.The gas both prevents oxidation and supports the pack — which is why a bag of crisps is inflated rather than merely sealed.Read more →
- Blanketing
- Maintaining a layer of inert gas above a liquid in a tank to keep oxygen away from it.Used on flammable solvents to hold the vapour space out of its flammable range, and on edible oils and resins to stop oxidation.
- Inerting
- Displacing the atmosphere inside equipment with an inert gas so nothing can burn or oxidise inside it.On flammable-gas plant this is a safety-critical step with a numeric acceptance test, not a formality.Read more →
Safety
- Asphyxiant
- A gas that harms by displacing oxygen rather than by being toxic.Nitrogen, argon and helium are simple asphyxiants. The body senses rising CO₂, not falling oxygen, so there is no breathless warning before collapse.Read more →
- Oxidiser
- A gas that does not burn itself but makes other materials burn faster, hotter and at lower ignition temperatures.Oxygen and nitrous oxide. This is why hydrocarbon contamination in a high-pressure oxygen system can ignite with no spark at all.Read more →
- Flammable range
- The band of gas-in-air concentrations that will ignite — below it too lean, above it too rich.Acetylene is 2.5–81% in air and 2.5–100% in oxygen, meaning no proportion of acetylene in oxygen is non-ignitable.Read more →
- Oxygen-deficient atmosphere
- Air containing less than 19.5% oxygen.Below about 10%, unconsciousness follows within seconds and with no warning sensation. Entry requires a permit, gas test at multiple depths and an attendant.
- Oxygen enrichment
- Air containing more than the normal 21% oxygen.Even 23–25% measurably lowers ignition temperatures and raises burning rates. Clothing saturated with oxygen ignites readily and burns faster than it can be removed.
- Adiabatic compression
- The heating that occurs when a gas is compressed rapidly, with no time for the heat to escape.Opening an oxygen cylinder valve quickly heats the gas downstream enough to ignite oil residue — which is why oxygen valves are opened slowly.
- Decomposition (acetylene)
- Acetylene breaking down into carbon and hydrogen, releasing heat — without needing any oxygen present.Confined decomposition raises pressure by ten to eleven times. It is the reason acetylene is generated below about 1.5 bar and stored dissolved.
- GHS
- The Globally Harmonised System for classifying and labelling chemical hazards.Standardises the pictograms, signal words and hazard statements that appear on a safety data sheet.Read more →
- SDS / MSDS
- A Safety Data Sheet — the document giving a substance’s hazards, first aid, handling, storage and transport information."MSDS" is the older name for the same document. A reference summary is not a substitute for the signed sheet for your specific supply.Read more →
- NFPA 704
- The diamond-shaped placard rating health, flammability, instability and special hazards from 0 to 4.Designed for emergency responders arriving at an incident, not for routine handling decisions.Read more →
- UN number
- The four-digit international identifier for a dangerous good in transport.Acetylene is UN 1001, oxygen UN 1072, nitrogen UN 1066, argon UN 1006. Argon is frequently mislabelled UN 1066, which is nitrogen.Read more →
- Confined space
- An enclosed or partly enclosed space not designed for continuous occupancy, where the atmosphere may be hazardous.Vessels, tanks, pits, trenches and cellars. Welding inside one with argon shielding is a confined-space operation and must be permitted and attended.
Purity
- Purity grade
- The stated minimum concentration of the named gas, with the balance being impurities and inerts.Over-specifying purity is a common way to waste a gas budget. Purging needs industrial grade; analytical instruments need 99.999%. Specify the application, not a number.
- UHP (ultra-high purity)
- The highest commercial purity grade, typically 99.999% and above.Needed where the instrument or process measures at the level the impurities occupy — analytical work, semiconductors, reactive-metal welding.Read more →
- Inerts / insolubles
- Nitrogen, oxygen, methane, hydrogen and argon carried in acetylene that no purifier can remove.They pass straight through every purifying medium. They also concentrate in a DA cylinder’s gas phase, so early discharge gas reads worse than the cylinder average.Read more →
- Phosphine (PH₃)
- A toxic hydride impurity in acetylene, formed from calcium phosphide in the carbide.Around 200 vpm in wet-generated gas. The principal target of the purifier, which takes it down to about 0.1 vpm.
- IP (Indian Pharmacopoeia)
- The pharmacopoeial standard medical gases are manufactured and released to in India.The difference between medical and industrial oxygen is this framework — batch testing, retained samples, release documentation and a controlled cylinder fleet.Read more →
- COA (certificate of analysis)
- The document stating the measured composition of a specific batch of gas.Worth requiring on purge nitrogen: cylinders labelled nitrogen have been found in the field to contain 19% and 48% oxygen.Read more →