Storage and handling of welding consumables
Storage and handling of welding consumables
consist of the following parts:
• Hydrogen induced cracking
• Coated electrodes
• Flux Cored Wires
• Submerged arc welding fluxes
of moisture in the coating, even after the final drying operation during manufacture. This moisture
decomposes in the arc during welding to give
hydrogen, (H), and consequential risk for hydrogen
induced cracking.
The moisture is bound in the crystalline structure
of some of the minerals in the coating and requires
a relatively high temperature to remove it. Basiccoated electrodes are designed to be dried at high
temperatures, resulting in a low coating moisture
level, and are often referred to as “low hydrogen
electrodes”.
Hydrogen induced cracking
Hydrogen in welded joints in ferritic materials can
give rise to hydrogen induced cracking, also known
as cold cracking and delayed cracking
The major factors which influence the risk of this
type of cracking are chemical composition of the
steel (Carbon Equivalent factor CE), cooling rate
and hydrogen content of the weld metal.
The most common sources of hydrogen are:
• Moisture in electrode coatings or SAW flux
• Drawing lubricants on cored wires
• Moisture in the atmosphere or shielding gas
• Condensation, rust, oil, paint or primer in the
weld joint area
Coated electrodes can be divided into:
1) Non-alloy C-Mn, rutile or acid-rutile coated
electrodes , with H>15 ml/100g weld metal.
2) Non-alloy C-Mn and low alloy, basic-coated
electrodes, with H<10 or <5 ml/100g weld metal.
3) High alloy austenitic stainless steel electrodes,
rutile or basic coated, where hydrogen diffusion
does not occur because hydrogen is soluble in
the austenitic atomic structure, even at room
temperature.
Moisture, lubricant etc. decomposes in the arc
during welding to give hydrogen,(H), which is
readily dissolved in the weld pool. On cooling this
(H) tries to escape via diffusion because it is less
soluble in the solid weld metal compared to the
molten weld pool. Any (H) that remains trapped
in the joint can cause hydrogen induced cracking.
Cracks generally form in the coarse-grained, HAZ
of the base material but for very high strength weld
metals cracks can also arise in the weld metal itself.
By following the recommended storage and handling procedures for welding consumables, moisture
levels can be minimised, along with the associated
hydrogen induced cracking risk.
Of the above listed groups, it is only types 1 and 2
which can give rise to hydrogen induced cracking.
For steel grades with a yield strength > 355MPa
the use of type 2 electrodes is recommended.
Type 3 electrodes are also dried at high temperature,
but this is to minimise the risk of porosity, also
caused by moisture in the coating.
Unfortunately, electrode coatings are hygroscopic,
i.e. they pick up moisture from the surrounding
atmosphere if freely exposed to it. Suitable coating
formulation design can minimise this effect but not
eliminate it. For this reason it is necessary to ensure
that electrodes are not able to absorb moisture (by
correct choice of packaging, storage and handling)
or, alternatively, to re-dry them before use.
Storage and handling of coated electrodes
Coated electrodes always contain a certain amount
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