Skip Navigation

Course 745 - Welding, Cutting, and Brazing Safety

Safety guides and audits to make your job as a safety professional easier

The Basics

In order to discuss the various aspects of welding, cutting and brazing safety, first we need to cover the basics in this first module. So let us get started.


Welding, Cutting, and Brazing

Welding is a process that joins materials together by melting a metal work piece along with a filler metal to form a strong joint. Heat metal parts to a temperature that is high enough to join the metal parts by coalescence.


Coalescence occurs when two metals seem to pull together, or grow into one body, of the base metal parts when there is the slightest contact. There are two basic requirements for coalescence: heat and intimacy of contact.

Heat: Welding processes differ depending on the source of heat, the manner in which heat is applied or generated, and the intensity of the heat. The fuel used as a heat force may be:

  • acetylene or hydrogen in air or in oxygen;
  • an electric arc;
  • an electric, gas, or oil furnace;
  • the resistance of metal to the flow of electric current; or
  • a chemical reaction between a metal oxide and finely divided aluminum.

The intensity of heat applied or generated at the joint varies according to the metals being joined and to the welding process being used. All welding processes, except brazing, use temperatures high enough to melt the base metals.

Intimacy of contact

In the second basic requirement for coalescence, intimacy of contact, you can divide the welding processes into two groups: pressure processes and non-pressure processes.

  • Pressure Processes: In pressure processes, there should not be any space between the surfaces being joined. Welders apply pressure while the contact surfaces are at a high enough temperature to allow plastic flow of the metal.
  • Non-pressure processes: In non-pressure processes, leave space between the joined surfaces. Fill this space, either progressively or all at once, with molten metal. The molten metal may be produced by:
    • a filler metal (welding rod or electrode),
    • melting the surfaces to be joined, or
    • combining a filler metal and melted base metal.

Read the material in each section to find the correct answers to each of the questions. After answering all questions, click the "Check Quiz Answers" button to see your score and a list of missed questions. To correct a question, return to the question, review the material, change your answer, and return to the last section page. Click the "Check Quiz Answers" again to recheck the results.

Do not refresh these pages or you'll have to answer all questions again.

Note: Videos and exercises in our courses are for information only and not required to view. Final exam questions will not be derived from the videos. OSHAcademy is not responsible for video content.

1. Which of the following occurs when two metals seem to pull together, or grow into one body, of the base metal parts when there is the slightest contact?

a. Melding
b. Coalescence
c. Phosphorescence
d. Penetration

Next Section


Brazing is a welding process using nonferrous filler alloys that do not contain iron or steel and have a melting point above 840°F but below that of the base metal. Brazing is also called ‘hard soldering’ or ‘silver soldering.’ Brazing is the only welding process in which the melting of the base metal is not necessary for coalescence. Click here for more information on brazing alloys.



Soldering is a joining process using non-ferrous filler alloys. Soft soldering uses alloys that melt between 190 to 840°F and is used in electronics, plumbing, and joining sheet metal parts. Soldering is not considered a welding process. Lead and tin are common alloys used in soldering, but there is also less common lead-free solder to decrease environmental impacts.


The term WELDABILITY, or joinability, means:

  • the ability of metal to be welded into a structure that will perform its purpose satisfactorily, and
  • the degree of simplicity of the procedures used to produce welds with properties that are equal to or better than the properties of the base material.

Many factors influence the weldability of metal, including:

  • the chemical composition of the metals involved;
  • the effect of radical temperature changes on the various elements;
  • the expansion and contraction characteristics of the base metals;
  • the filler metal (welding rod or electrode);
  • the joint design; and
  • the welding procedure.

2. The ability of metal to be welded into a structure that will perform its purpose satisfactorily is called _____.

a. coalescence
b. weldability
c. soldering
d. designability

Next Section

Filler Materials and Flux

filler materials

The metals added during the welding process are known as filler materials or filler metals. In welding processes in which space is left between the parts to be joined, filler metals provide the intimacy of contact necessary for coalescence. Filler materials used in welding processes include welding rods and electrodes.

Welding Rods: The term welding rod refers to a filler metal, in wire or rod form, used in gas welding and brazing processes and in certain electric welding processes (tungsten inert gas) in which the filler metal is not a part of the electric circuit. A welding rod serves only one purpose—it supplies filler metal to the joint.

As a rule, rods are uncoated except for a thin film resulting from the manufacturing process. Welding rods for steel are often copper-coated to protect them from corrosion during storage. Most rods are furnished in 36-inch lengths and a wide variety of diameters, ranging from 1/32 to 3/8 inch. Rods for welding cast iron vary from 12 to 24 inches in length and are frequently square rather than round in cross section. The rod diameter selected for a given job is governed by the thickness of the metals being joined.

Electrodes: In electric welding, electrodes form a part of the electrical circuit. In gas tungsten arc welding, electrodes melt off and are a source of the filler metal supply.

  • Solid Electrodes- These electrodes are consumable (composed of steel, copper, aluminum, various alloys, and other metals) or non-consumable (primarily tungsten). They produce less fumes, compared with flux-cored wire or coated electrodes.
  • Covered and Coated Electrodes- These are the largest group of electrodes used in welding. The covering provides the flux from the weld. Major metals from the coatings include fluoride, nickel, iron, chromium, manganese, copper, and molybdenum.
flux rods 123 rf photo
Click to Enlarge

Fluxes: Welding or brazing certain materials requires the use of flux to produce a sound joint. Fluxes are available as liquids, pastes, and powders. They have a melting point below that of the base and filler metals, and they are not incorporated into the weld. Their primary purpose is to prevent the formation of oxides on the weld joint before and during welding operations. Fluxes should never be used as a substitute for proper cleaning.

Observe the following precautions when you are working with fluxes.

  • Unless the base metal is properly cleaned and the correct flux applied to the joint, fluxing will hinder rather than aid in making the joint.
  • Flux should not be overheated, or it will fail to serve its purpose.
  • Fluxes will also deteriorate if they are kept at brazing temperatures for too long.
  • Fluxes should always be used in a well-ventilated space.

3. What is the only purpose of a welding rod?

a. To provide intimacy of contact for coalescence
b. To complete the electrical welding circuit
c. To supply filler metal to the joint
d. To provide adequate flux to the metal

Next Section

Click to Enlarge

Oxyacetylene Cylinders

Oxyacetylene equipment consists of a cylinder of acetylene, a cylinder of oxygen, two regulators, two lengths of hose with fittings, a welding torch with tips, and either a cutting attachment or a separate cutting torch.

Accessories include a friction igniter to light the torch, an apparatus wrench to fit the various connections on the regulators, the cylinders, and the torches; goggles with filter lenses for eye protection; and gloves for protection of the hands. Flame-resistant clothing is worn when necessary.


Click to Enlarge

Reduce the gas pressure in a cylinder to a suitable working pressure before it can be used. This is done by a regulator or reducing valve. Regulators are either the single-stage or the double-stage type:

  • Single- stage regulators reduce the pressure of the gas in one step;
  • two-stage regulators do the same job in two steps or stages. Less adjustment is generally necessary when two-stage regulators are used.

Acetylene regulators and oxygen regulators are of the same general type, although those designed for acetylene are not made to withstand such high pressures as are those designed for use with oxygen cylinders.

Welding Torches

Click to Enlarge

The oxyacetylene welding torch is used to mix oxygen and acetylene gas in the proper proportions and to control the volume of these gases burned at the welding tip. Torches have two needle valves, one for adjusting the flow of oxygen and the other for adjusting the flow of acetylene. They have a handle (body), two tubes (one for oxygen and one for acetylene), a mixing head, and a tip. Welding tips are made from a special copper alloy, which dissipates heat (less than 60 percent copper), and are available in different sizes to handle a wide range of plate thicknesses.


Hoses used to make the connection between a torch and a regulator are strong, nonporous, and flexible and light enough to make torch movements easy. It is made to withstand high internal pressures, and the rubber used in its manufacture is specially treated to remove sulfur to avoid the danger of spontaneous combustion.

The hoses used for acetylene and oxygen are the same in grade, but they differ in color and have different types of threads on the hose fittings. The oxygen hose is GREEN, and the acetylene hose is RED. For added protection against mixing of the hoses during connection, the oxygen hose has right-hand threads and the acetylene hose has left-hand threads. The acetylene fittings also have a notch that goes around the circumference of the fittings for an additional identification factor.

4. Oxyacetylene equipment has two hoses: the oxygen hose is _____ and the acetylene hose is _____.

a. blue, orange
b. orange, blue
c. red, green
d. green, red

Next Section

Welding Defects

Common weld defects that you should be familiar with to ensure your safety include:

  • Incomplete fusion: Incomplete fusion occurs when the weld fails to fuse one side of the joint in the root. Click the button to see an illustration.
  • Incomplete Fusion

  • Inadequate joint and root penetration: Inadequate joint and root penetration is cause for rejection of a weld even if it is sound in all other respects. The strength required in a weldment is achieved only when the specified joint and root penetration is achieved.
  • Lack of Penetration

  • Spatter: Spatter is the term used to describe metal particles or globules expelled during welding and that do not form part of the weld. When spatter occurs, small balls of metal are stuck to the surface of the base metal along the line of weld.
  • Spatter and Crater

  • Overlap: Overlap is a protrusion of the weld metal beyond the bond at the toe of the weld.
  • Undercut: An undercut is a groove melted into the base metal adjacent to the toe and not filled with weld metal.
  • Root cracks: Root cracks are similar to toe cracks except that they occur at the root of the weld. Root cracks may be in the weld metal or in the base metal.
  • Toe cracks: Toe cracks occur in the base metal, at the toe of the weld.
  • Toe Cracks

  • Crater cracks: One common kind of crack is the crater crack. This occurs in the crater or depression at the termination of a weld bead in gas or arc welding.
  • Underbead cracks: Underbead cracks occur in the heat-affected zone underneath a bead and do not extend to the surface of the metal.
  • Underbead Cracks

  • Voids: Voids, also called gas pockets or blow holes, occur as the result of gas being absorbed during the welding and then trapped as the metal solidifies.
  • Inclusions: Slag inclusion is the term used to describe the weld defect in which non-metallic solid material is trapped in the weld metal or at the bond between the weld metal and the base metal.

5. Metal particles or globules that are expelled during welding and that do not form part of the weld are called _____.

a. spatter
b. cracks
c. craters
d. voids

Check your Work

Read the material in each section to find the correct answer to each quiz question. After answering all the questions, click on the "Check Quiz Answers" button to grade your quiz and see your score. You will receive a message if you forgot to answer one of the questions. After clicking the button, the questions you missed will be listed below. You can correct any missed questions and check your answers again.

Next Module