TWI Frequently asked questions
by John Weston
Oxy-fuel welding includes those welding operations which use the combustion of a fuel gas and oxygen to provide sufficient heat for fusion welding. Definitions given in the Standards include:
BS499: Part 1 1991 Glossary for welding, brazing, and thermal cutting
33 001 gas welding:
Fusion welding, with or without filler metal, in which the heat for welding is produced by the combustion of a fuel gas or gasses with an admixture of oxygen.
O33 002 oxy-acetylene welding:
Gas welding in which the fuel gas is acetylene. NOTE. Other fuel gases are also used with oxygen (i.e. butane, hydrogen, and propane): In such cases appropriate alterations to the term and the definition arenecessary.
ISO 4063 Welding, brazing, soldering and braze welding of metals - Nomenclature of processes and reference numbers for symbolic representation on drawings
| 3 | Gas welding; fuel gas welding |
| 31 | Oxy-fuel gas welding |
| 311 | Oxy-acetylene welding |
| 312 | Oxy-propane welding |
| 313 | Oxy-hydrogen welding |
| (32 | Air-fuel gas welding |
| 321 | Air acetylene welding |
| 322 | Air-propane welding) |
The reference numbers for the process are used in welding procedures and on drawings to clarify requirements.
These processes involve melting of the parent metal, with or without a filler wire addition, using a flame produced at the nozzle of a welding torch. The fuel gas and oxygen are combined, in the correct proportions, inside a mixingchamber which is part of the welding torch.
The process has several features that can be beneficial in specific circumstances. For example, the welder has good control over heat input, temperature and filler metal addition, all of which can be altered independently.Furthermore, the flame chemistry can be altered from reducing (carburizing) through neutral to oxidising. The equipment is of low cost and highly portable. However, productivity is generally low compared with other fusion weldingprocesses. Heat input is also higher than using an arc welding process for the same application. Mechanical properties, particularly toughness, are not as good compared with arc welding and, as a result, the process is seldom usedwhere high integrity welded joints are required.
Most common users are heating pipework installation and automotive repair.
For welding, there should be:
- a high flame temperature
- a high rate of flame propagation
- adequate heat content
- minimum (controlled) chemical reaction between the flame and the weldment
Of the commercial fuel gases, acetylene most closely meets all of these requirements.
Further information
The oxyacetylene welding process
Equipment for oxyacetylene welding
