the hot metal in a weld area. Several methods have been devised to ‘shield’ the weld area from these naturally occurring air elements. The three most common types of arc welding in the construction industry are known by their shielding methods.
5.11.1.1. Shielded Metal Arc (SMA). The most widely used arc welding method is
‘Shielded Metal Arc’, also known as the ‘Coated Stick Electrode’ method. With this method, the electrode is factory coated with a flux material that releases an inert gas as it is melted which repels oxygen and nitrogen. The flux can also contain alloying elements which affect tensile
strength, hardness, corrosion resistance, and other physical properties of the weld metal. The stick is consumable, and must be manually fed into the weld by the welder operator as the weld progresses.
Electrode sticks are available in an array of sizes, strengths, and fluxes. Each is identified by a code number EXXXX, where E stands for electrode, and each X represents a number.
The first two (or three) numbers indicate the minimum tensile strength, in ksi of the deposited metal in the as-welded condition. For example E70XX is a common electrode, with an as-welded strength of 70 ksi (we’ll get to the other X’s in a minute). This 70 ksi will be higher than the tensile strength of nearly any steels being welded.
The next number refers to the position in which the electrode will make a satisfactory weld: 1 means all positions (flat, vertical, overhead, and horizontal); 2 means flat and horizontal fillet welds; and 3 means flat only.
The last number indicates the electrical current to be used and the type of coating on the electrode. For example, there are high-cellulose sodium coatings for use with direct-current reverse polarity (electrode positive); or iron powder, titania coatings for use with direct current - either polarity, or alternating current;
and others. So if you should encounter an E6018 electrode, you will know that it has a minimum tensile strength of 60 ksi; may be used in all positions; and has an iron-powder, low hydrogen coating, suitable for alternating or direct current – reverse polarity.
The decision of which stick electrode to use is generally left up to the welder, with the
exception that the engineer will usually specify
the as-welded strength. Structural welding is an elaborate science, and must be performed only by highly trained, certified individuals (see following section on welder certification).
One of the most important, yet most commonly violated aspects of shielded metal arc welding is that the electrode sticks be stored and
maintained so as to keep them out of the atmosphere until the time they are to be used.
This is because the flux coating will absorb water vapor and other detrimental constituents of air only to be released directly into the weld area, thereby defeating the purpose of the flux and compromising the weld.
Question: “The building inspector told me I have to bake my electrodes in an oven before I can use them on the jobsite. First of all, I don’t bake; and even if I did, this is an incredible hassle. Why can’t I just grab an electrode out of the package, fire up the welder and go?”
Answer. The building inspector is doing his best to be sure that your welds are top quality. If your electrodes are not in a factory hermetically sealed container, they must be oven heated to drive out the water vapor that the flux has absorbed. There are other rules about storing electrodes in ovens, maximum number of
‘reheats’, maximum time between oven and use, and so on.
5.11.1.2. Submerged Arc Welding. This is a process similar to shielded metal arc, with the exception that the flux is not pre-adhered to the electrode stick; it is supplied in granular form, and is applied separately as the weld progresses. Because the flux blankets the weld zone, the arc is not visible, hence the term
‘submerged’ arc. The welding electrode is usually fed (and consumed as the weld
progresses) automatically from a coiled reel.
This process is well adapted to flat or horizontal applications where long straight welds are called for. With this process, high heat - high
penetration welds are easily obtained, and the speed of the weld is much faster than with shielded metal arc.
5.11.1.3. Gas Metal Arc (or gas
shielded arc) Welding. This is the third type of arc welding common in the construction
industry. A continuous spooled consumable electrode is fed into the weld zone through a hand held ‘stinger’. Shielding of the weld zone is accomplished in either of two ways. An external gas supply floods the weld zone with an inert gas or gas mixture (which usually contains an inert gas). With this method, the electrode can be bare metal (no flux), but welding must commence in a windless (usually shop) environment so the gas is not blown from the weld zone. This type of welding is sometimes called Metal Inert Gas or MIG welding.
The other way the weld zone is shielded is through the use of an electrode which has flux in the core of it, thus the name flux cored arc welding.
When external gas is used, it is stored in a steel
‘bottle’ and is an integral part of the welding rig.
You will occasionally hear the term wire feed welding; this is gas metal arc welding.
5.11.2. Welding Position. This refers to the position the welded metal is in relative to the welder. When a welder operator wishes to become certified, there are four basic welding positions that he must be proficient in.
Flat position is where the weld is made from the top of a nearly horizontal surface, and
the top of the weld itself is horizontal. This is the fastest and easiest type of welding.
The flat position is slightly different from the horizontal position. This is where one of the members being welded is in a vertical position and the other is horizontal. In this case, the top of the weld is not flat, but at a 45 degree angle.
The third position is vertical. This is where the weld is applied to members standing vertically. This is more difficult and time consuming than flat or horizontal.
The fourth, and most difficult position is overhead; where the weld is applied upside down (overhead).
5.11.3. Types of Welds. There are four basic types of welds: fillet, grove, plug, and slot. Note that these are types of welds, not types of welding processes (shielded metal arc, gas metal arc, etc.) nor types of welding positions (horizontal, flat, vertical, etc.).
5.11.3.1. Fillet Welds. These are perhaps the most common, wherein two pieces of metal at 90 degrees (or close to 90 degrees) to each other are joined by a weld at the intersection. With a fillet weld, the pieces of metal are not grooved or otherwise modified at the location of the weld. Weld material is simply laid down at the intersection of the pieces of metal.
The weld is triangular in cross section. The size of a fillet weld is the length of the longest leg of the weld in cross section. The throat is the distance from the deepest part of the weld to the surface. If the weld face is convex, then the throat distance is more critical than the leg distance, because it represents the weakest
potential fracture plane of the weld. If the weld is flat or concave, the leg distance is the critical distance.
Fillet welds most commonly occur in the size range 3/16” to 5/16”. The minimum allowable size of fillet welds depend on the thickness of metal being joined. For example, the minimum size fillet for any material 0.25” and smaller is 1/8”. For material between 0.25” and 0.5” thick, minimum fillet size is 3/16”. Fillet welds may be larger than 5/16”, but if so, they must be made by multiple passes. After each pass, the slag (slag is a waste by-product of burnt flux that adheres to the weld) must be thoroughly chipped from the weld before the next pass is applied. This is inefficient and expensive. If a fillet weld is made along the edge of a member, it may not be larger than the thickness of the
‘edge member’.
5.11.3.2. Groove Weld. This is a weld that is made in a gap or groove between the
pieces of metal being joined. There are nine types of grooves:
square
single-V
double-V
single-bevel
double-bevel
single-U
double-U
single-J
double-J
Groove welds are classified by the amount of penetration through the thickness of the members being joined as follows:
L = limited base metal thickness, complete joint penetration
U = unlimited thickness, complete joint penetration
P = partial joint penetration.
Whenever you hear ‘full penetration weld’, a groove weld is being referred to in which the weld extends the full depth of the members being joined. Most of the high strength welded joints used in the construction industry are full penetration or partial penetration groove welds.
These are stronger than fillet welds because there is much more penetration of the weld into the joint; and thus greater bonding of the weld to the members being joined is achieved.
There are many pre-qualified groove weld joints shown in the literature. Pre-qualified means that the weld is standardized; it has been designed and tested and is reliable in it’s capacity so long as the listed procedure is followed. If non-pre-qualified welds are desired, they must be tested and approved prior to actual use (a procedure that is expensive, time consuming and very seldom done). Strictly speaking, even when pre-qualified welds are used, there must be a written procedure created by the welder operator available on-site which lists: amperage; wire feed speed; voltage; travel speed; and shielding gas flow rate.
5.11.3.3. Plug and Slot Welds. Plug welds are created by depositing weld material into a circular hole cut in one of two lapped members. Slot welds are similar, except that the hole is elongated, not circular. In both cases, the hole can be partially or completely filled.
These are used to supplement fillet welds on lapped members when there is not enough fillet weld space. They are also used to prevent buckling of lapped parts.
5.11.4. Types of Welded Joints. There are five basic types of welded joints: butt, corner, tee, lap, and edge.
Butt joints are made to members lying in approximately the same plane.
Corner joints are made between members at approximately 90 degrees to each other.
Tee joints are similar to corner joints, except that the intersection forms a tee instead of a corner.
An edge joint joins the edges of two or more parallel (or nearly parallel) parts.
A lap joint is formed at the intersection of two overlapping parts.
5.11.5. Primary and Secondary Welded