Oxy-Fuel by the Numbers

About this book

An oxy-fuel torch looks simple: two hoses, two valves and a flame. Behind it sits a chain of gas supply, pressure control, mixing, combustion and oxidation in which every link can be measured. When the measurements are taken, the torch stops being a matter of feel and becomes something a workshop can set up, compare, cost and make safer on evidence.

This book is for the people who run that chain or answer for it: fabrication supervisors, manufacturing engineers, estimators, safety officers and experienced tradespeople. It assumes you have seen oxy-acetylene equipment in use and are comfortable with simple algebra, percentages and SI units. It does not teach hand skills; those come from supervised practice. It teaches the numbers behind the hand skills, so that settings, cylinders, hoses, arrestors and quotes can be checked rather than inherited.

A 1921 investigation as the starting point

In 1918 the United States Army asked the Bureau of Standards to find out which oxy-acetylene welding and cutting blowpipes were efficient, safe and well made. The result, published as Technologic Paper No. 200 in 1922, is one of the earliest systematic trials of the equipment. Apparatus from fourteen manufacturers was tested on standard steel with standard gas. Consumption was measured by weighing the gas banks on large balances and checked with purpose-built orifice flow meters. Cutting was done by machine so the operator’s hand could not bias the results.

Its conclusions were blunt. None of the cutting blowpipes was economical across all thicknesses, most ran with preheat flames that were too large, and none of the welding blowpipes was free from flashback. The investigator traced flashback to back pressure at a partly blocked tip upsetting the mixture inside the torch, and showed that experienced operators habitually set an oxidising flame while believing it neutral. Those findings are a century old. The physics behind them is not, and much of modern practice, from two-stage regulators to flashback arrestors, answers problems the 1921 trials put on paper.

Each chapter takes one part of the investigation, explains it in modern terms and asks what current practice adds.

The running case

This is an illustration. A regional Australian fabrication workshop must cut 60 base plates, each 400 × 400 mm, from 25 mm grade 250 steel plate for a conveyor upgrade. Counting all four edges of each plate, that is 96 m of cut. The workshop has a portable track cutting machine and hand torches, an oxygen manifold and acetylene cylinders. Through the book it compares three cutting settings, sizes its gas supply, checks its regulators and hoses, measures its consumption, audits its flashback protection, examines its cut edges and prices the job. The workshop, its settings, flows, speeds, prices and results are invented for teaching. They are not KEVOS® work, and they are not manufacturer’s data for any nozzle or torch.

How to use the book

Read Chapters 1 to 6 in order if you are responsible for the equipment: they move from fair testing and flame chemistry through cylinders, pressure and flow to flashback. Chapters 7 to 9 cover cutting and its cost and can be read on their own by estimators and engineers. Chapter 10 brings the work together in a record of the cutting station. Every chapter ends with an exercise and its worked answer. Calculations use cubic metres of gas at 15 °C and 101.325 kPa unless stated, and the 1921 imperial figures are converted where they help.

Limits and professional responsibility

This book is educational. Oxy-fuel equipment stores and burns flammable and oxidising gases under pressure, and its hazards include fire, explosion, burns, fumes and confined spaces. In Australia the work is governed by work health and safety laws, regulators’ codes of practice, Australian Standards such as AS 4839, and the gas supplier’s and equipment maker’s instructions. Nothing here replaces them, competent training or the judgement of a qualified person on site. The 1921 procedures are described as history, not as practice. Where a figure comes from a published source it is cited; where it comes from the running case it is labelled as an illustration and must be replaced with your own measured or supplier data before any real decision.

An original treatment

READOS already compares cutting processes in Choosing a cutting process for plate and sheet, which places oxy-fuel beside laser, plasma and waterjet. This book goes inside the oxy-fuel process itself. The explanations, the base-plate case, the calculations, figures and exercises are original KEVOS® writing. The 1921 paper is a public United States Government document; its methods and findings are summarised and analysed in new words, and none of its text, tables or illustrations is reproduced.