Welding Allied’s galvanized steel tubing is a very achievable operation if three key points are observed to assure consistent quality results.
- Use sound welding practices and procedures
- Practice proper safety rules
- Adopt good weld restoration methods
Use of Sound Welding Practice
Tubular steel should be welded so as to develop the adequate strength at all connections between tubes; accordingly, the required weld configuration and size should be specified on the drawings by the designer. When tubes are butt welded (i.e., joined end-to-end), the weld should penetrate through the full tube wall thickness and reinforcement should not exceed 3/32 inches (2.5 mm). When the joint design is a tee, corner or fillet weld, the size and length required should be shown on the drawing. For the convenience of the designer, the following weld sizes will provide welds that have a throat dimension that is at least equal to the thickness of the tube being joined. When tubes of different wall thicknesses are joined, the minimum fillet weld size can be based on the thinner of the members.
|Tube Wall Thickness (in.)||Minimum Fillet Weld Size||Tube Wall Thickness (in.)||Minimum Fillet Size|
|0.035||0.063 (1/16")||0.113||0.160 (3/16")|
|0.049||0.069 (3/32")||0.133||0.186 (3/16")|
|0.065||0.092 (3/32")||0.14||0.198 (7/32")|
|0.072||0.102 (1/8")||0.145||0.205 (7/32")|
|0.083||0.117 (1/8")||0.154||0.217 (7/32")|
|0.095||0.134 (5/32")||0.18||0.250 (1/4")|
|0.109||0.134 (5/32")||any thickness(t)||1.414 x (t)|
These fillet weld sizes are suitable for tee and angle joints where the tube end is coped to match the outside diameter of the mating tube or where the tube end is flattened so that contouring is not needed. The numbers in parentheses are the nearest larger fraction of the required weld size and match standard fillet gauge sizes.
While there is no maximum fillet size, but over-sized welds do not make the weld perform better. Similarly, it takes more time to make over-sized welds – and this costs money.
Completed welds should be visually examined and exhibit no gaps, voids, cracks, undercut, porosity or arc strikes; they should be reasonably smooth and uniform. Weld spatter should be removed particularly if the surface being welded will be restored by painting or coating.
Fillet welds sizes should be verified using a fillet weld gauge. These are simple go-no go gauges that can be purchased from you local welding supplier, or they can be machined from heavy sheet metal for specific sizes. Where the drawing specifies welding all around a joint, the weld size should meet minimum drawing requirements all around the joint.
Sound Welding Process and Procedures
GAS METAL ARC (“MIG”) WELDING
This process is by far the most widely used welding process when welding Allied’s tube because it has makes high-quality welds quickly.
The first choice is to use the Spray Transfer mode. Use 0.035 inch ER70S-2 or ER70S-3 wire, 92% Argon/8% CO2 shielding gas, a welding gun rated at 400 amps or more and a power source rated at 400 amps, 100% duty cycle. Follow the table below. Travel speed will be high and deposition rates (i.e. production rate) will be high.
When welding 16 gauge and thinner galvanized steel, it may be necessary to use the short circuiting transfer mode. The power source should be rated at 200 amps or more at 100% duty cycle, and it should have “inductance” control. Use 0.035 inch ER70S-2 or ER70S-3 wire, 92% Argon/8% CO2 shielding gas, a welding gun rated at 300 amps. Set the inductance to maximum and the slope control (if any) between mid-range and maximum slope. Follow the settings in the table below. If the welder has difficulty keeping the stickout constant, switch to 0.030 inch diameter wire and adjust the wire feed speed to use approximately the amperage shown above.
|Spray Transfer||Short Circuiting|
|Volts:||27 to 30||17 to 20|
|Amps:||250 to 380||100 to 190|
|Wire Feed Speed (ipm):||280 to 450||100 to 210|
|Dial Location (o'clock):||1 to 3||9 to 11|
|Tip Position:||Recessed 1/4"||Extended 1/4"|
|Gas Flow Rate:||25 to 30 CFH||25 to 30 CFH|
|Spatter indicates that:||Arc voltage too low||Arc voltage too high|
The wire stickout should be held constant during welding. If the welder pulls the torch away from the workpiece, the stickout gets longer and the arc voltage will increase causing spatter if the welder is using short circuiting transfer. If the welder brings the torch closer to the workpiece, the stickout gets shorter, reducing the voltage across the arc and increasing spatter if the welder is using spray transfer. Welders should understand how to these facts; that is, the welder needs to get the voltage settings right (i.e., set it for minimum spatter) and then be aware that increasing or decreasing the stickout affects the voltage across the arc and the amount of spatter that is developed. One of the best resources training using GMAW can be found at Weld Reality.
Some of fabricators have had success welding galvanized tube using E70C-6 metal cored wire such as Hobart’s Galvacor; the parameters given above are a good starting point for metal cored wire. Others have found that self-shielded flux cored wire conforming to E71T-14, such as Lincoln’s Innershield NR-152 and ESAB’s CoreShield 10 work well for some work since a shielding gas is not needed. Follow the electrode manufacturer’s recommended settings with flux cored wire.
The above recommends starting with a shielding gas of 92% argon/8% CO2. If welding on tube that is 12 gauge thicker, or to thick parts, the CO2 can be increased to as much as 18%. This increases the arc energy, ensuring penetration into thicker steel. Conversely, if you are welding 18 gauge or thinner, the CO2 can be reduced to 2%. If burn-through is a problem, switch to 98% Argon/2% Oxygen gas mixture and reduce the voltage by 2 to 3 volts. Use of Argon/Oxygen mixtures is not recommended for tube thicknesses over 1/8 inch.
A gas that develops noticeably less zinc fume when welding galvanized tube is Praxair’s Helistar GV; however, since it is a helium/argon/CO2 mixture, it is more expensive than argon-based shielding gas.
SHIELDED METAL ARC (“STICK”) WELDING
Due to its low productivity, this process should be used where GMAW cannot be used, such as outdoors where wind would make use of a gas-shielded process impractical. Allied’s galvanized steel tube can be welded using 3/32 inch diameter E6013 electrode with direct current and electrode positive (reverse polarity) or alternating current and the parameters recommended by the electrode manufacturer. When welding tube to thicker materials, E6010 should be used to ensure penetration into the thicker material.
GAS TUNGSTEN ARC (TIG, HeliArc) WELDING
This process also has low productivity but can make very sound welds between galvanized components. Welding of thinner gauge galvanized steel can be done using direct current, electrode negative (straight polarity), 1/16″ diameter EWTh-2 tungsten pencil-sharpened with a 1/32″ flat end, ER70S-2 or ER70S-3 filler metal, argon shielding gas and the following parameters:
|Gauge||Thickness (in.)||Amps for Grooves||Amps for Fillets||Filler Diameter|
|18 to 22||0.028 to 0.047||35 to 65||40 to 60||1/16" or 3/32"|
|14 and 16||0.059; 0.079||45 to 75||65 to 90||3/32"|
|12||0.105||65 to 90||95 to 105||3/32"|
|10+||0.135||70 to 100||110 to 130||3/32"|
GTAW is the slowest and costliest of the welding processes, and it should be used only where visual appearance is critical and mechanical surface treatment for appearance is not practical.
Proper Safety Practices
When a manufacturer uses welding, he needs to be aware of safety hazards associated with welding. These include Welding Smoke and Fumes, Electrical Shock, Electromagnetic Radiation.
Welding and Smoke Fumes
Welding produces smoke and fumes which come up from the weld zone in what is referred to as a plume. Obviously, the smoke and fumes which result from welding are not especially healthy to breathe!
The most-cost effective thing a company with welding fumes and smoke is to teach its welders to keep their heads out of the fume plume. Supervisory personnel should be instructed to watch for welders whose heads are in the plume and advise them to change positions. Welders should set up their work so that air flows from one side to the other, rather than towards or from behind the welder. This will keep the plume (and its contents) away from the welder’s breathing zone. When there is a ceiling height of 16 feet or more, and a space of 10,000 cubic feet per welder, and no confined spaces, natural ventilation is considered adequate. When these criteria are not met, forced ventilation must be provided according to American National Standards Institute (ANSI) standard Z49.1*. This may be done by using a mobile hood or exhaust hose which can be placed in the vicinity of welding, or by using a fixed enclosure which will provide an air flow rate of 100 feet per minute (1 to 2 MPH) in the vicinity of welding. Ventilation can also be in the form of open grid work tables with uniform downdraft ventilation providing at least 150 cubic feet of air per minute per square foot of table surface. Finally, a low volume, high-velocity fume educator may be attached to the welding gun to provide local fume removal.
The USFDA recognizes that at least 15 mg/day of zinc is essential for proper health in humans. Zinc is also a necessary micronutrient for plant and animal life. Too much zinc, however, can cause temporary illness known as “metal fume fever.” Inhaling the white zinc oxide which is produced when welding zinc may cause temporary symptoms of influenza, including fever and chills. No permanent or long-term effects are known to occur. It is important that the welding plume containing the zinc oxide be carried away from the welder. ANSI Z49.1* requires that zinc fume removal be done by local exhaust ventilation when zinc is welded indoors. Welders should also be taught not to stand or work downwind from another welder who is welding on zinc coated materials. In addition to local or general ventilation, personal breathing filters are recommended. Light-weight, disposable, half-face filters such as the 3M™ Welding Fume Respirator or the Dust/Fume/Mist filter (#9920) are convenient for the welder, and no maintenance is required. Half-face mask cartridge filters using filter elements designed for metal fume removal are also acceptable and available from 3M. Powered air purifying systems and supplied air systems such as the 3M™ Adflo™ Powered Air Purifying Respirator (PAPR) are also available from 3M. These systems provide combined respiratory, head, eye and face protection for situations in which fume exposure cannot be avoided.
*This Standard as well as Welding Safety and Health Fact Sheets are available free from the American Welding Society, Miami, Florida.
Welders and those who work around welding need to be aware that there is sufficient voltage in a welding circuit to cause severe injury. When using a standard arc welding machine, there is 80 volts of difference between the welding electrode and the surrounding work piece and building; when using a continuous wire process, such as MIG or Flux core, this difference is around 40 volts. Welders are usually aware of the potential hazard, but others who work around welding are frequently unaware of this danger. This situation should be regularly addressed during safety meetings.
When using any arc welding process, an electrical arc is generated which emits various forms of electromagnetic radiation energy, including light. The most harmful of this radiation is ultraviolet light which can cause blindness with excessive exposure. Welders know to wear adequate protection from radiation when they are welding. Those who work around welding, however, must also protect themselves. This is usually done by placing either opaque or translucent but ultraviolet absorbing barriers around the area where welding is being done. This radiation can also burn skin, so the welder and those who work around welding should wear protective clothing to avoid the hazard. Eye protection should consist of wearing polycarbonate safety glasses with side shields. Polycarbonate absorbs the most harmful ultraviolet radiation, preventing eye damage. In addition, this practice will prevent “Welding Flash Burn” (sunburn of the white of the eyeball), which is usually caused by reflection of the arc from surrounding objects, including walls.
Restoring Corrosion Protection
The heat from welding vaporizes the protective zinc coating near the weld. Even though the remaining zinc continues to provide some protection to the zinc-free areas, the appearance is poor, and the zinc-free areas will rust when exposed to the environment. Paints which are high in elemental zinc (i.e., “zinc-rich”), properly applied, will effectively restore full corrosion protection to the weld areas. These paints are available in either spray cans or in containers suitable for brush or spray application. This paint can be applied to the weld after sand blasting or wire brushing to remove all welding slag followed by wiping the weld clean with a rag.
Thermal sprayed zinc is also effective in restoring corrosion resistance, but the surface has to be sufficiently roughened, usually by sand blasting ir coarse abrasive conditioning to enable thermal-sprayed zinc to stick properly.