Welding Rods
(Thoriated Tungsten Electrodes)
Welding Rods
(Thoriated Tungsten Electrodes)
Are you saying that welding rods are radioactive?
Sometimes. Certain welding rods, often referred to as thoriated tungsten
electrodes, do indeed contain some radioactivity.
What exactly are thoriated tungsten electrodes?
Thoriated tungsten electrodes were introduced approximately fifty years ago
as an alternative to the use of pure tungsten electrodes. The word "thoriated"
means that each of the electrodes contains a small amount (1or 2% by weight)
of thorium dioxide (ThO2).
Where are these things used?
Thoriated tungsten electrodes are widely used in commercial industries, such
as aircraft, petrochemical, construction, and food processing, in a process
known as tungsten inert gas, or "TIG" welding. In TIG welding, an electrical
arc is produced between a nonconsumable tungsten electrode and the work metal.
This heats up the metal in the process.
Why are these rods made of tungsten?
Tungsten is the predominant ingredient in the electrodes because of its high
melting temperature, which exceeds that of all other metals.
Well then, what is Thorium?
Thorium is a radioactive element that occurs naturally in our environment.
In fact, thorium can be found in all of the soil and rocks on earth to some
degree or another. It is a relatively heavy, metallic element. An atom of
thorium contains, in its nucleus, 90 positively-charged particles,known as
"protons", and a varying number of neutral particles, known as "neutrons",
depending upon the isotope.
Remind me again what an isotope is?
Sure. An isotope of an element has the same number of protons in its
nucleus as the stable element, but a different number of neutrons. The primary
radioactive isotope of interest in the thoriated tungsten products is
Thorium-232, or Th-232. You can read more about radioisotopes, radioactive
decay, and where sources of radioactivity like Th-232 are found by reviewing
some of the other chapters in this "Radioactivity Basics" section of the
IEM web page.
Are thoriated tungsten electrodes big in size?
I guess its a matter of perspective, but usually not. A typical electrode
has a diameter on the order of one-eighth of an inch (1/8") and a length
of approximately one-half foot (6"), although several other diameters and
lengths are available. In fact, the manufacturers of these items frequently
make them in sizes that are specific to a particular operation or need.
It seems funny that thoriated tungsten electrodes are used for welding
when plain tungsten rods, without the thorium, would avoid the need for the
radioactivity. Why is that?
Thoriated tungsten electrodes are preferred by some welders over the pure
tungsten ones because they result in improved welding properties. The addition
of thorium to this tungsten product results in easier arc starting, greater
arc stability, reduced weld metal contamination, higher current-carrying
capacity, and a longer electrode lifetime.
So do all welding rods contain thorium?
No. There are non-radioactive alternatives available. In fact, the use of
these products should always be considered when the advantages of thoriated
devices are neither required nor necessary.
Let's assume I can't live without the thoriated tungsten ones. Are
there potential risks associated with their use?
Radiation emitted from all radioactive materials interacts with the atoms
in tissue by knocking off their electrons or creating charged particles,
called ions. It is the process of ionization that, if the amount is high
enough, causes health effects such as tissue damage or increased cancer risk.
Because thoriated tungsten electrodes contain radioactivity, they can ionize
living tissue through the pathways of both external and internal radiation
exposure.
What do you mean by the external exposure pathway?
The external exposure pathway refers to ionizing radiations emitted external
to the body by the elctrode. When those radiations interact with and
impact the body, that is called an external exposure. However, the
risk associated with the external exposure from handling these devices in
any practical quantity is negligible.
Okay then, what about the internal exposure pathway?
Internal exposure occurs when radioactive materials are taken into the body.
This is applicable to the use of thoriated tungsten electrodes because welding
and grinding operations that use them typically result in the loss of material
from the electrode.
Why is that?
During the welding process itself, the arc releases small amounts of thorium
into the air. And grinding of electrodes, which is required periodically
in order to achieve the fine, conical tip necessary for quality welding of
heat sensitive metals, has the same result. When thorium particles become
airborne, they can then be inhaled by the welder and result in an internal
radiation dose.
Oh my. This sounds serious.
But its not. Remember, just because something is radioactive doesn't
make it a radiological health hazard. Although the magnitude of
the dose associated with the use of welding rods can be measured, it is small
in comparison to other radiation exposures one typically receives every day
of their lives by virtue of being alive. In fact, the average annual dose
incurred by users of thoriated tungsten electrodes is less than 0.3% of the
maximum permissible dose for occupational radiation workers . . . and the
agencies who promulgates this dose limit considers annual doses less than
the limit to be "safe".
So there are no effects whatsoever?
Although there is a statistical probability that the use of thoriated tungsten
electrodes could cause lung cancer, the theoretical probability is vanishingly
small. In reality, this effect has never been demonstrated. Nonetheless,
we encourage you to take some time to review the "Radiation Risks" chapter
to learn more about the difference sbetween statistical and real
radiation-related health effects.
What precautions should I take when storing and using thoriated tungsten
electrodes?
While the radiation hazard from these devices is low, based on scientific
studies that have been conducted by a variety of commercial firms and approved
by regulatory agencies, like any industrial device, product or compound,
there are some "common-sense" precautions that will lower the potential risks
even further.
Like what?
For example, when not in use, welders should avoid storing the electrodes
anywhere on their bodies, like in a shirt pocket.
Okay, that makes sense. What about protective clothing? Should I wear
that?
Clothing and devices that are typically worn during welding operations, such
as gloves, face shield, and normal work clothes, afford excellent radiological
as well as physical protection. Once again, this a common sense kind-of thing.
Any other suggestions?
Just a few. Welding should not be performed in confined spaces unless
supplemental ventilation is provided. And it stands to reason that individuals
that are not directly involved with the welding operation should stand back
from the work location. During grinding operations, the area near the operator
should be ventilated and the loss of material from the electrode as a result
of this operation should be vacuumed or suctioned on a routine basis. And
last but not least, once the operations have ceased, normal hygiene practices,
such as washing your hands, is encouraged.
When I'm done with a thoriated tungsten electrode, how do I dispose of
it?
Technically-speaking, you may dispose of these devices the same way you dispose
of any other industrial materials of this type. There are no federal regulatory
restrictions on their disposal by conventional means.
I hear a bit of a hesitation in your voice. Are there exceptions?
No, there aren't . . . when you're done with the electrodes, you can dispose
of them any way you want. However, if large disposals are anticipated, it
would be worthwhile to have some preliminary discussions with your local
landfill operator in order to avoid any misunderstandings.
Why would there be a misunderstanding?
Many operators, in this day and age, monitor incoming waste shipments for
radioactivity. If you or your employer drives a truck through the gates of
the site, that truck will often pass through a portal or gate monitor. If
you have enough tungsten electrodes in the truck, the gate monitor will alarm,
which notifies the operator. He or she is then likely to look at the driver,
sternly, and demand an explanation.
I see what you mean. So if I get preliminary approvals, I won't put my
drivers in dicey positions, right?
Right.
You said that it was perfectly legal to dispose of thoriated tungsten
electrodes in landfills. Legal in who's eyes? Who is it that makes
these decisions?
The regulation of tungsten-thorium alloys falls under the jurisdiction of
the U. S. Nuclear Regulatory Commission, or the NRC. The NRC is a federal
radiation agency that issues licenses for the possession of radioactivity.
Don't tell me I need a license just to use a couple of welding
rods?
No, no . . . a license is not required. Under the NRC's provisions of Title
10 of the Code of Federal Regulations, Part 40 (10CFR40), Domestic Licensing
of Source Material, the receipt, possession, use, or transfer of these devices,
as long as their thorium content is less than 4 percent by weight, is exempt
from licensing requirements. In other words, the NRC's basic position regarding
thoriated tungsten electrodes is that it is neither reasonable nor necessary
to regulate their possession and use.
Are there any other regulatory agencies with a say in this?
The Department of Transportation, or DOT, is another federal agency that
is involved only to the extent that its regulations in Title 49 of the Code
of Federal Regulations, require the container carrying thoriated tungsten
products during transport from the manufacturer to the store that sells them
to be labeled with the word "radioactive" and the proper UN number (ID 2910).
The shipper must also confirm that the package itself exhibits a contact
exposure rate of less than 0.5 millirem per hour.
How do exposures from thoriated tungsten electrodes compare to natural
background radiation I receive on an annual basis?
The Natural Council on Radiation Protection and Measurements, a body of national
experts, publishes reports on a variety of issues of interest to the radiation
protection community and offers recommendations. NCRP Report No. 95,
Radioactivity in Consumer Products, describes the use of thoriated electrodes
and their potential dose to the population. According to the NCRP, use of
thoriated tungsten electrodes involves exposures to a small number of people
and a small resulting dose to the exposed and general populations. The NCRP
estimates that the average annual effective dose equivalent to the exposed
population, which is predominantly the welders, is a maximum of 16 millirem.
(Check out the glossary in the "Tool Box" section of the IEM web page for
a definition of these units.) This value can be compared to the range of
background and medical doses incurred by members of the U.S. population each
year, which is from 250 to over 1,000 millirem.
Well this is all very interesting. I can see that while thoriated tungsten
electrodes for welding contain radioactivity, they can be used and disposed
of safely, and that I should not worry too much, right?
Pretty much. Widespread use of thoriated tungsten electrodes continues due
to their inherent advantages over the use of pure tungsten electrodes. And
while they do contain radioactive material and must be labeled as such during
transport, studies in the workplace have shown that the hazard to the welder
and any assisting personnel is not significant and does not require the use
of special ventilation or protective clothing. In addition, no federal authority
requires licensing of these materials and no use limitations for these devices
by federal or recommending bodies in this country have been promulgated.
And the radiation doses are low too.
That's right. Estimated doses from the uses of these devices are well below
those received on an annual basis from natural background radiation. At the
same time, however, the user should be aware that a potential internal hazard
to body tissues from the use of these devices does exist. For that reason,
common safety procedures should be followed. In addition, the use of
non-radioactive alternatives, which are presently available, should be considered
on a case-by-case basis.
Thank you. I think I'll go out and weld something.
Okay. But take some welding lessons first. We don't want you to burn
yourself!
Copyright © 2001 Integrated Environmental Management, Inc.