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Low Hydrogen Electrode Classification Question
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(Aerospace)
(OP)
9 Aug 12 20:55Im studying for the CWI exam for my retest I failed the code book portion for the exam. One thing that I am stumped on is low hydrogen electrode designation. Heres where im stuck. The question reads: What is the minimum preheat temperature for welding a 1 inch thick ASTM A36 plate with an E electrode? Now I know what the answer is it's 50 degrees. What im puzzeled on is that in table 3.2 in the D1.1 edition, for ASTM 36 plate preheat and interpass temp theres two answers SMAW with other then hydrogen electrodes or SMAW with low hydrogen electrodes. Now obviously an E electrode is a low hydrogen electrode because the answer is in the low hydrogen electrode preheat specification. What my question is, is what designates an electrode to be low hydrogen or other then low hydrogen? I know that A5.1 classifies for steel electrodes and A5.5 classifies for low alloy electrodes. But I also found that low hydrogen electrodes can be classified in either A5.1 or A5.5. Stumped if I run into another question asking similar like E or E how do I know where to look, either in low hydrogen electrodes or other then low hydrogen electode? Please help thanks.
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(Petroleum)
10 Aug 12 08:13If I understand your question, a SMAW electrode with the four digit designation ending with 5,6, or 8 will signify a LH electrode.
E701x
E801x
x = 5, 6 or 8 is a LH electrode
(Materials)
10 Aug 12 08:37Under AWS classification, like AWS 5.5, for low hydrogen designation the diffusible hydorgen designator must be described. This reqires testing to be performed under AWS 5.5 of low hydrogen electrode classifications.
So, for AWS E the suffix designator would be defined as either E- H16, H8, or H4, etc.,
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(Aerospace)
(OP)
10 Aug 12 18:04Ohhh ok I see yeah listed in the F groups is the designation, also after looking at the 5,6, or 8 at the end of the classification. Anything in F group F4 or ending with a 5,6,8 is a LH electrode. thanks Guys!!
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Stick welding is a skill that takes much practice to master, and selecting the correct electrode for the job can be equally challenging. Stick electrodes are available in a wide range of types, each of which provides different mechanical properties and operates with a specific type of welding power source. Factors you should consider when selecting a stick electrode include base metal type, joint fit-up and welding positions. Before you power up your machine and pick up your electrode holder, consider these basic guidelines.
The first step in choosing an electrode is to determine your base metal composition. Your goal is to match (or closely match) the electrode composition to the base metal type, which will help ensure a strong weld. If you're in doubt about the composition of your base metal, ask yourself these questions:
To prevent cracking or other weld discontinuities, match the minimum mechanical properties of the electrode to the mechanical properties of the base metal. You can identify a stick electrode's tensile properties by referring to the first two digits of the EN ISO classification printed on the label of the electrode box. For example, the number '42' on an E 42 5 B 42 H5 classified electrode indicates that the filler metal produces a weld bead with a minimum yield strength of 420 MPa and a minimum tensile strength of 500 MPa and, as a result, would work well with a steel of similar yield / tensile strength.
Some electrodes can be used with only AC or DC power sources while other electrodes are compatible with both. To determine the correct current type for a particular electrode, refer to the digit after the letter describing the coating type of the EN ISO classification (E 42 5 B 42 H5). This digit represents the nominal efficiency and type of compatible welding current.
The type of current you use also influences the penetration profile of the resulting weld. For example, a DCEP compatible electrode, delivers deep penetration and produces an extremely tight arc. It also has the ability to 'dig' through rust, oil, paint and dirt. A DCEN compatible electrode provides mild penetration and works well when bridging two joints or welding high speed, high current fillet welds in the horizontal position.
An AC compatible electrode, such as an unalloyed rutile electrode, produces a soft arc with medium penetration and should be used to weld clean, new sheet metal.
Thick materials require an electrode with maximum ductility and low hydrogen to prevent weld cracking. Electrodes with coating type B (basic covering) according to EN ISO classification provide excellent low'hydrogen properties and good toughness (high impact values) to accommodate for residual stress.
For thin materials, you will need an electrode that produces soft arcs, such as a rutile. Also, smaller diameter electrodes will provide shallow penetration to help prevent burn-through on thinner materials.
To determine what position(s) a particular electrode is qualified for, always refer to the last digit before the Hydrogen symbol H in EN ISO classification (E 42 5 B 42 H5) . Here's how you decipher the qualified electrode position (according to ISO ):
1 = PA, PB, PC, PD, PE, PF, PG
2 = PA, PB, PC, PD, PE, PF
3 = PA, PB
4 = PA
5 = PA, PB, PG
For example, a E 42 5 B 42 H5 electrode can be used in all positions except vertical down.
Next, make sure to assess the conditions that the welded part will encounter throughout its service. If it will be used in high heat or low temperature environments, subjected to repetitive shock loading, a low hydrogen electrode with higher ductility will reduce the chance of weld cracking. Also, be certain to check for welding specifications if you're working on critical applications such as pressure vessel or boiler fabrication. In most cases, these welding specifications will require you to use specific types of electrodes.
To achieve the best results, you should always remove excessive mill scale, rust, moisture, paint and grease. Clean base metals help prevent porosity and increase travel speeds. If cleaning your base metal is not possible, Elga P 43 or P 47D electrodes deliver a deep penetrating arc that has the ability to cut through contaminants.
Consideration of the above factors will help you overcome the challenges of selecting the correct stick electrode for your particular application. However, given the wide range of available electrodes, several solutions may exist for one application. If you need additional assistance with electrode selection, your local ITW Welding sales representative or your local Elga distributor can serve as an excellent resource.
Download your free copy of Guide to EN ISO -A
Article based on ITW Welding global experience and knowledge.
Tags: MAXETA, Problem Solving, Stick Welding, Welding