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FOREWORD:
This bulletin is issued to alert dealers and users of welding
hose that special hose may be necessary for use with
certain fuel gases.
SCOPE:
This bulletin relates to welding hose manufactured in
conformance to RMA/CGA specification or to welding hose
conforming to individual manufacturer or user specifications.
CAUTION:
The fuel gases listed below are recorded to alert welding
hose users to a potential hazard with these or similar gases.
It should be noted that no condemnation of any of the gases
listed is intended. The purpose is to advise against the use of
hose that may not be designed for a particular gas or pressure.
A user of any fuel gas is urged to relate the type of gas along
with the expected working pressure (regulator setting) to the
hose manufacturer for a specific hose recommendation.
ALERT LISTING:
These and similar fuel gases may damage some grades or
types of welding hose:
APACHE, FLAMEX, MAPP, PROPANE, PROPYLENE.
Use of the indicated or similar fuel gases at regulator settings
above 40 psi may be particularly hazardous.
Users are also alerted against the use of ACETYLENE at
any pressure above 15 psi.
IN-SERVICE CAUTION:
The user is first cautioned to shut off the gas at the torch
and then at the regulator or supply source when the torch
will not be used for periods in excess of 30 minutes, in order
to limit permeation of gas through the hose wall.
The user is further cautioned not to shut off the fuel gas at
the regulator or supply source first as a flashback may result
and thereby damage the hose.
Adequate ventilation must be provided in confined areas
where fuel gas is being used to prevent the accumulation or
concentration of gas that could be explosive or otherwise
harmful to personnel.
BACKGROUND INFORMATION:
The RMA/CGA specification for welding hose, as originally
promulgated, considered welding hose that would be used
to convey the then common fuel gas, acetylene, at the
recommended low pressure (15 psi). Several grades were
described, the variance between grades relating to a
difference in their resistance to deterioration in the presence
of oil, or to their resistance to destruction by flame, or both.
No differentiation was made for a variance in performance
resulting from exposure to the fuel gas itself. It had been
determined that actylene, when conveyed under the low
pressures common to its recommended use, had little effect
on hose, regardless of its composition or construction.
In recent years, there have been developed or adopted a
number of fuel gases based on specific hydrocarbons or
mixtures of hydrocarbons. It is known that these special fuel
gases have a different effect on rubber compounds than
does acetylene. The precise effect on all the many and
varying hose compounds and constructions of the many
manufacturers has not been determined for all the known
special fuel gases.
The effect of any material being conveyed in a hose on the
rubber compounds used in the hose can be measured by
one or several test procedures. In the case of fuel gases,
the test procedures most applicable would be designed to
measure a change of the physical properties after exposure
to the fuel gas including tensile, elongation, hardness
and volume.
A characteristic of rubber hose that is significant in its use
as welding hose is a phenomenon known as permeation.
Any gas confined in the bore of a hose exhibits a tendency
to pass through the tube wall and subsequently through the
reinforcement and cover to the environment. Each gas has
its own specific characteristic tendency to permeate. Each
rubber compound exhibits specific resistance to permeation.
The rate of permeation increases with higher temperature.
To minimize the permeation of fuel gas through the hose
wall it is logical to design the tube compound for the lowest
possible permeation rate. The problem in the case of welding
hose results from the variety of gases now encountered,
the varying pressures used in service, and the varying
temperatures to be found in the work place. The need to
ventilate the work place is evident, both for maintaining
the lowest practical temperature and to dissipate the
permeating gas, however slight, to prevent buildup to
concentrations that are either explosive or dangerous for
breathing by workmen.
Some rubber compounds are known to have low permeation
rates with several fuel gases but no specific rule can be
laid down to predict overall performance. Thus, it becomes
advisable to check the characteristic of each hose construc-
tion with each gas under actual or simulated service
conditions to qualify it for use.
CAUTION:
Users of welding hose are urged to communicate their
service conditions to the hose manufacturer and obtain
the best recommendation of the manufacturer for a hose
suitable for those conditions.
* Reprinted with permission from the Rubber Manufacturers Association (RMA)
Hose Handbook, RMA/IP-2/2003.
WELDING HOSE TECHNICAL INFORMATION
PRECAUTIONS IN THE USE OF WELDING HOSE
WARNING: The use of certain fuel gases may damage welding hose and lead to fires and explosions.
TECHNICAL REFERENCE
C