Introduction to Gas Welding and Cutting

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A. Bhatia, B.E.

Course Outline

Oxy-fuel process uses heat created by combustion of fuel (commonly acetylene) to melt the base material and create fusion bond with or without a filler material. It is extremely versatile process and has tremendous power of creating, repairing and destroying the work of man.

This 4 hours online course provides understanding of oxy-acetylene welding and cutting, as well as safety practices.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the reader will be knowledgeable about:

• The principles of oxy-acetylene process;
• Types of gases and their potential applications;
• Advantages and limitations of oxy-acetylene process;
• Identify oxy-gas equipment, cylinder types, their identification and storage;
• Use of ancillary equipment such as hoses, regulators, blowpipes and safety devices;
• Oxy-acetylene welding and cutting practices;
• Proper operation, care and safe handling of oxy-acetylene equipment;
• Types of flames and their uses;
• Selection of tip size for fuel pressures to obtain a neutral flame;
• Equipment assembly and testing procedures;
• Lighting up and shutting down procedures;
• Identify operational faults and immediate action to be taken; and
• Understand safe practices in use of oxy-acetylene equipment.

Intended Audience

This course is aimed at anyone who has to operate oxy-acetylene/propane cutting equipment for use in the repair and maintenance of plant and equipment, and any supervisors/managers overseeing this operation.

Benefit to Attendees

Attendees of this course will help you get started welding using the oxy-acetylene apparatus and understand the safety features associated with each component. The course will be extremely helpful to the readers who desire to build on their knowledge on oxy-acetylene process and the skilled professionals who have learnt the trade informally on the job.

Course Introduction

Oxy-fuel welding is a process that uses heat created by a gas flame to melt the base material. The gas flame created by combustion of oxygen and acetylene produces temperatures of 5600 to 6000 degrees, which is the hottest of any gas flame and is capable of melting almost any metal. In case of welding, two parts are brought to a molten condition along the line to be joined and fused together. In cutting operation, one piece of metal is brought to a red heat and is then cut in two by an oxidizing flame. Oxy-acetylene cutting can be used to cut thicknesses from 2/8″ to up to 12″.

This course provides understanding of oxy-acetylene welding and cutting, as well as safety practices.

Course Content

This course content is in the following PDF document:

Introduction to Gas Welding and Cutting

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Course Summary

Oxy-acetylene welding is simple in concept - two pieces of metal are brought together, and the touching edges are melted by the flame with or without the addition of filler rod. Cutting with the oxy-fuel process is just the opposite from of welding. Oxy-fuel cutting uses acetylene and oxygen to preheat metal to red hot and then uses pure oxygen to burn away the preheated metal. Because this is achieved by oxidation, it is only effective on metals that are easily oxidized at this temperature. Such metals are mild steel and low allow steels.
A standard oxy-acetylene equipment setup consists of an oxygen tank, an acetylene tank, regulator and gauges, gas hoses, a torch and tip. Characteristics of the oxy-acetylene welding process include:

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• Its ability to switch quickly to a cutting process, by changing the welding tip to a cutting tip;
• The high temperature the gas mixture attains (~5800°F);
• The use of regulators to control gas flow and reduce pressure on both the oxygen and acetylene tanks;
• The use of double line rubber hoses to conduct the gas from the tanks to the torch;
• Melting the materials to be welded together;
• The ability to regulate temperature by adjusting gas flow.

It can be used on any thickness of metal; however there are some serious safety issues owing to the extreme flammability of acetylene and high pressure of the oxygen cylinders.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

Gas Cutting

Oxyfuel gas cutting (also referred to as oxyfuel cutting or gas cutting) is a rather popular variation of thermal cutting process applied at industrial level. There are several different variations of gas that can be used to perform this process, with a noticeable variation of the end results.

One of the biggest reasons for why it is so popular is the range of materials that it can cut – the material thickness that gas cutting can work with ranges from 0.5mm to 250mm. The equipment costs for gas cutting are also relatively cheap by industry standards, and the entire process can be performed mechanically, and not just manually.

The process of gas cutting

Fundamentally speaking, the gas cutting process is relatively simple – in its most basic form, a gas cutting machinery is a nozzle that directs both the primary oxygen stream, as well as several secondary streams of the combination of oxygen and gas that serves as a fuel.

The metal piece in question gets preheated first using the combination of gas and oxygen (to about 700-900 degrees Celsius, a so-called “ignition” temperature). In this state, the metal piece is not hot enough to melt, but still hot enough for the cutting process to be conducted.

After heating up the metal piece in question, the primary nozzle directs a stream of oxygen to the heated piece, instigating a chemical reaction between the metal piece and the oxygen. This reaction creates a “slag”, or iron oxide, that immediately gets blown away by the same oxygen stream that initiated the reaction, allowing for the nozzle itself to proceed with cutting the metal piece.

Gas cutting as a whole has four main prerequisites to be conducted in the first place:

• The level of oxygen dilution should be as little as possible, since it can negatively impact the performance of the cutting process as a whole.
• As we’ve mentioned before, the metal piece’s temperature must be below melting point for the cutting process to proceed as planned.
• The scope of oxidation reaction between the metal and the oxygen must be large enough for the ignition temperature to stay at the same level.
• The melting point of the created oxide must be lower than the current temperature of the metal, or the “slag” would not be blown away by the oxygen stream.

It’s important to mention that different materials (stainless steel, various non-ferrous metals, cast iron, etc.) have different oxide melting levels, which creates a requirement of adding powder to lower the oxide melting temperature and to create a “slag” that can be blown away.

Different gas types

It should not be a big surprise that gas cutting can use different gas variants to perform gas cutting processes. There are three main characteristics that can be used to distinguish some specific fuel gas type:

• The volume of gas that is needed for the combustion process to begin;
• The highest possible flame temperature – usually at the tip of the inner cone;
• The produced heat of the combusted gas.

There are five main types of gas that are regularly used to perform gas cutting processes – natural gas, MAPP, acetylene, propylene and propane. We can go over each and every one of them in a bit more detail.

Natural gas

One gas type that has the lowest performance out of all five here is natural gas. Its heat distribution levels are at 1,490 kj/m^3, which is at least ten times less than three of the four remaining gas types. It has the slowest piercing speed and the lowest peak flame temperature (2,770 degrees Celsius), and not that low of a ratio between fuel gas and oxygen – 1.8 to 1.

MAPP (Methylacetylene-propadiene)

As the gas type goes, MAPP is a combination of propadiene, methylacetylene, as well as some other hydrocarbons. Its performance is quite average as a whole, with 2,976 degrees Celsius peak flame temperature and relatively high heat release levels for both primary and secondary flames (15,445 kj/m^3 and 56,431 kj/m^3, respectively). This combination of parameters makes it a relatively average gas type in terms of cutting speed, but it can be used at higher pressure levels, which makes it a great choice for various underwater cutting procedures.

Acetylene

If we’re looking for a gas type with the highest flame temperature (3,160 degrees Celsius), acetylene is the one we’re looking for. Of course, the highest peak temperature makes acetylene the gas type with one of the fastest cutting speeds out of all of them. Its flame is also way faster than something like propane, and it is mostly focused on the inner cone, reducing the overall area of the metal that is affected by heat, and thus reducing the distortion percentage as a whole.

Propylene

Another interesting variation of a gas type is propylene, which is a liquid petroleum gas. It offers a rather average peak flame temperature (about the same as MAPP – 2896 degrees Celsius), but can compensate with a high level of heat release in the outer cone – about 72,000 kj/m^3. At the same time, it also has a rather big disadvantage of having a high fuel gas volume requirement – 3.7 to 1 oxygen to fuel gas ratio.

Propane

Propane is the last gas type out of five, producing a rather low peak heat level, but offering a higher area of effect for the heat around the nozzle. While the overall propane nature makes the cutting flame a bit more spread-out when compared with something like acetylene, the overall cutting speed is on par with said acetylene – even if the piercing speed is slower, as a consequence of lower peak heat level (2,828 degrees Celsius).

Gas cutting in Levstal

Gas cutting is quite a versatile process that has several different gas types and nozzle arrays, offering different variations of cutting for various use cases. Levstal specialists use two ESAB SXE-P1 4500 machines for oxygen jet cutting (gas cutting), and are capable of working with black sheet metal with the following parameters: thickness 15 – 150 mm, width up to 2800 mm, cut length up to 18000 mm.

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