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General theory about Welding

GENERAL
Welding is any metal joining process wherein coalescence is produced by heating the metal to suitable
temperatures, with or without the application of pressure and with or without the use of filler metals.
Basic welding processes are described and illustrated in this manual. Brazing and soldering, procedures
similar to welding, are also covered.

METALS
a. Metals are divided into two classes, ferrous and nonferrous. Ferrous metals are those in the iron class
and are magnetic in nature. These metals consist of iron, steel, and alloys related to them. Nonferrous
metals are those that contain either no ferrous metals or very small amounts. These are generally divided
into the aluminum, copper, magnesium, lead, and similar groups.
b. Information contained in this circular covers theory and application of welding for all types of metals
including recently developed alloys.

SAFETY PRECAUTIONS IN WELDING OPERATIONS
GENERAL SAFETY PRECAUTIONS
GENERAL
a. To prevent injury to personnel, extreme caution should be exercised when using any types of welding
equipment. Injury can result from fire, explosions, electric shock, or harmful agents. Both the general
and specific safety precautions listed below must be strictly observed by workers who weld or cut
metals.
b. Do not permit unauthorized persons to use welding or cutting equipment.
c. Do not weld in a building with wooden floors, unless the floors are protected from hot metal by means
of fire resistant fabric, sand, or other fireproof material. Be sure that hot sparks or hot metal will not fall
on the operator or on any welding equipment components.
d. Remove all flammable material, such as cotton, oil, gasoline, etc., from the vicinity of welding.
e. Before welding or cutting, warm those in close proximity who are not protected to wear proper
clothing or goggles.
f. Remove any assembled parts from the component being welded that may become warped or otherwise
damaged by the welding process.
g. Do not leave hot rejected electrode stubs, steel scrap, or tools on the floor or around the welding
equipment. Accidents and/or fires may occur.
h. Keep a suitable fire extinguisher nearby at all times. Ensure the fire extinguisher is in operable
condition.
i. Mark all hot metal after welding operations are completed. Soapstone is commonly used for this
purpose.

PERSONAL PROTECTIVE EQUIPMENT
a. General. The electric arc is a very powerful source of light, including visible, ultraviolet, and infrared.
Protective clothing and equipment must be worn during all welding operations. During all oxyacetylene
welding and cutting proccesses, operators must use safety goggles to protect the eyes from heat, glare,
and flying fragments of hot metals. During all electric welding processes, operators must use safety
goggles and a hand shield or helmet equipped with a suitable filter glass to protect against the intense
ultraviolet and infrared rays. When others are in the vicinity of the electric welding processes, the area
must be screened so the arc cannot be seen either directly or by reflection from glass or metal.

b. Helmets and Shields.

(1) Welding arcs are intensely brilliant lights. They contain a proportion of ultraviolet light which
may cause eye damage. For this reason, the arc should never be viewed with the naked eye within
a distance of 50.0 ft (15.2 m). The brilliance and exact spectrum, and therefore the danger of the
light, depends on the welding process, the metals in the arc, the arc atmosphere, the length of the
arc, and the welding current. Operators, fitters, and those working nearby need protection against
arc radiation. The intensity of the light from the arc increases with increasing current and arc
voltage. Arc radiation, like all light radiation, decreases with the square of the distance. Those
processes that produce smoke surrounding the arc have a less bright arc since the smoke acts as a
filter. The spectrum of the welding arc is similar to that of the sun. Exposure of the skin and eyes
to the arc is the same as exposure to the sun.

(2) Being closest, the welder needs a helmet to protect his eyes and face from harmful light and
particles of hot metal. The welding helmet is generally constructed of a pressed fiber
insulating material. It has an adjustable headband that makes it usable by persons with different
head sizes. To minimize reflection and glare produced by the intense light, the helmet is dull
black in color. It fits over the head and can be swung upward when not welding. The chief
advantage of the helmet is that it leaves both hands free, making it possible to hold the work and
weld at the same time.

(3) The hand-held shield provides the same protection as the helmet, but is held in
position by the handle. This type of shield is frequently used by an observer or a person who
welds for a short period of time.

(4) The protective welding helmet has lens holders used to insert the cover glass and the filter
glass or plate. Standard size for the filter plate is 2 x 4-1/4 in. (50 x 108 mm). In some helmets
lens holders open or flip upwards. Lenses are designed to prevent flash burns and eye damage by
absorption of the infrared and ultraviolet rays produced by the arc. The filter glasses or plates
come in various optical densities to filter out various light intensities, depending on the welding
process, type of base metal, and the welding current. The color of the lens, usually green, blue, or
brown, is an added protection against the intensity of white light or glare. Colored lenses make it
possible to clearly see the metal and weld. Table 2-1 lists the proper filter shades to be used. A
magnifier lens placed behind the filter glass is sometimes used to provide clear vision.

FIRE HAZARDS

a. Fire prevention and protection is the responsibility of welders, cutters, and supervisors.
Approximately six percent of the fires in industrial plants are caused by cutting and welding which has
been done primarily with portable equipment or in areas not specifically designated for such work. The
elaboration of basic precautions to be taken for fire prevention during welding or cutting is found in the
Standard for Fire Prevention in Use of Cutting and Welding Processes, National Fire Protection
Association Standard 51B, 1962. Some of the basic precautions for fire prevention in welding or cutting
work are given below.

b. During the welding and cutting operations, sparks and molten spatter are formal which sometimes fly
considerable distances. Sparks have also fallen through cracks, pipe holes, or other small openings in
floors and partitions, starting fires in other areas which temporarily may go unnoticed. For these reasons,
welding or cutting should not be done near flammable materials unless every precaution is taken to
prevent ignition.

c. Hot pieces of base metal may come in contact with combustible materials and start fires. Fires and
explosions have also been caused when heat is transmitted through walls of containers to flammable
atmospheres or to combustibles within containers. Anything that is combustible or flammable is
susceptible to ignition by cutting and welding.

d. When welding or cutting parts of vehicles, the oil pan, gasoline tank, and other parts of the vehicle are
considered fire hazards and must be removed or effectively shielded from sparks, slag, and molten
metal.
e. Whenever possible, flammable materials attached to or near equipment requiring welding, brazing, or
cutting will be removed. If removal is not practical, a suitable shield of heat resistant material should be
used to protect the flammable material. Fire extinguishing equipment, for any type of fire that may be
encountered, must be present.

HEALTH PROTECTION AND VENTILATION

a. General.
(1) All welding and thermal cutting operations carried on in confined spaces must be adequately
ventilated to prevent the accumulation of toxic materials, combustible gases, or possible oxygen
deficiency. Monitoring instruments should be used to detect harmful atmospheres. Where it is
impossible to provide adequate ventilation, air-supplied respirators or hose masks approved for
this purpose must be used. In these situations, lookouts must be used on the outside of the
confined space to ensure the safety of those working within. Requirements in this section have
been established for arc and gas welding and cutting. These requirements will govern the amount
of contamination to which welders may be exposed:
(a) Dimensions of the area in which the welding process takes place (with special regard to height of ceiling).
(b) Number of welders in the room.
(c) Possible development of hazardous fumes, gases, or dust according to the metals involved.
(d) Location of welder's breathing zone with respect to rising plume of fumes.

(2) In specific cases, there are other factors involved in which respirator protective devices
(ventilation) should be provided to meet the equivalent requirements of this section. They
include:
(a) Atomspheric conditions.
(b) Generated heat.
(c) Presence of volatile solvents.

(3) In all cases, the required health protection, ventilation standards, and standard operating
procedures for new as well as old welding operations should be coordinated and cleaned through
the safety inspector and the industrial hygienist having responsibility for the safety and health
aspects of the work area.

b. Screened Areas. When welding must be performed in a space entirely screened on all sides, the
screens shall be arranged so that no serious restriction of ventilation exists. It is desirable to have the
screens mounted so that they are about 2.0 ft (0.6 m) above the floor, unless the work is performed at
such a low level that the screen must be extended closer to the floor to protect workers from the glare of
welding.

c. Concentration of Toxic Substances. Local exhaust or general ventilating systems shall be provided
and arranged to keep the amount of toxic frees, gas, or dusts below the acceptable concentrations as set
by the American National Standard Institute Standard 7.37; the latest Threshold Limit Values (TLV) of
the American Conference of Governmental Industrial Hygienists; or the exposure limits as established
by Public Law 91-596, Occupational Safety and Health Act of 1970. Compliance shall be determined by
sampling of the atmsphere. Samples collected shall reflect the exposure of the persons involved. When a
helmet is worn, the samples shall be collected under the helmet.

NOTE
Where welding operations are incidental to general operations, it is considered good
practice to apply local exhaust ventilation to prevent contamination of the general work
area.

d. Respiratory Protective Equipment. Individual respiratory protective equipment will be well retained.
Only respiratory protective equipment approved by the US Bureau of Mines, National Institute of
Occupational Safety and Health, or other government-approved testing agency shall be utilized.
Guidance for selection, care, and maintenance of respiratory protective equipment is given in Practices
for Respiratory Protection, American National Standard Institute Standard 788.2 and TB MED 223.
Respiratory protective equipment will not be transferred from one individual to another without being
disinfected.

e. Precautionary Labels. A number of potentially hazardous materials are used in flux coatings,
coverings, and filler metals. These materials, when used in welding and cutting operations, will become
hazardous to the welder as they are released into the atmosphere. These include, but are not limited to,
the following materials: fluorine compounds, zinc, lead, beryllium, cadmium, and mercury. See
paragraph 2-4 i through 2-4 n. The suppliers of welding materials shall determine the hazard, if any,
associated with the use of their materials in welding, cutting, etc.

(1) All filler metals and fusible granular materials shall carry the following notice, as a minimum,
on tags, boxes, or other containers:
CAUTION
Welding may produce fumes and gases hazardous to health. Avoid breathing these fumes
and gases. Use adequate ventilation. See American National Standards Institute Standard
Z49.1-1973, Safety in Welding and Cutting published by the American Welding Society.

(2) Brazing (welding) filler metals containing cadmium in significant amounts shall carry the
following notice on tags, boxes, or other containers:
WARNING
CONTAINS CADMIUM - POISONOUS FUMES MAY BE FORMED ON HEATING
Do not breathe fumes. Use only with adequate ventilation, such as fume collectors,
exhaust ventilators, or air-supplied respirators. See American National Standards Institute
Standard Z49.1-1973. If chest pain, cough, or fever develops after use, call physician
immediately.

(3) Brazing and gas welding fluxes containing fluorine compounds shall have a cautionary
wording. One such wording recommended by the American Welding Society for brazing and gas
welding fluxes reads as follows:
CAUTION
CONTAINS FLUORIDES
This flux, when heated, gives off fumes that may irritate eyes, nose, and throat.
Avoid fumes--use only in well-ventilated spaces.
Avoid contact of flux with eyes or skin.
Do not take internally.

f. Ventilation for General Welding and Cutting.
(1) General. Mechanical ventilation shall be provided when welding or cutting is done on metals
not covered in subparagraphs i through p of this section, and under the following conditions:
(a) In a space of less than 10,000 cu ft (284 cu m) per welder.
(b) In a roan having a ceiling height of less than 16 ft (5 m).
(c) In confined spaces or where the welding space contains partitions, balconies, or other

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1 comments:

asharani said...

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Welding Electrode Plant and Machineries Exporter

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