May 22, 2007
The prices of materials consumed in your welding shop aren't the only materials-related economic considerations. How you use those materials affects the bottom line. Monitoring compressed-gas usage and looking for areas of waste can improve your shop's financial picture. This article offers practical suggestions for reducing waste.
Photo courtesy of Hobart Brothers.
Resource purchase price and utilization have an impact on welding shop economics. Both have real value, but the latter is by far a more practical concern.
The general work forces in today's factories and industries are considerably smaller, less formal, and much less structured than those of yesteryear. Operations have changed drastically. Frequently a few employees wear many hats, and the responsibility for keeping operation costs in check often falls on these few. Shop floor laborers lack the training and the responsibility for monitoring costs.
Staying functional in a competitive market is a day-to-day struggle. This article serves as a guide for checks and balances internal departments can use in their weld shops to monitor compressed-gas cylinder usage.
Purchase price or waste: Which has the highest price tag? Cost and what contributes to cost by the day, week, month, or year will be reviewed in short "power information" statements and examples witnessed over the past 30 years. They may not all apply to all shop environments, but they all are worth a review and attention.
To me, waste means continuously spending a dollar for something that should cost only 50 cents, or buying five of something and routinely throwing two or three away. Multiplying these occurrences by 100 or 1,000 times over a year or five years depletes very precious operations capital.
Throwing away or diverting profit dollars from investments and new equipment disturbs me. I don't believe waste is all part of doing business today, as I've heard so many times. True, some waste is undeniably necessary, but in today's industry, it has a higher price tag.
A topic least understood by the welding industry is compressed-gas cylinder waste and the associated costs. Prices used in the examples presented in this article are a nominal average based on my experience.
The cost of compressed gas in New York or Chicago has a structural variance difference from that of a high-volume account in Elkhart, Ind., Atlanta, or the shipyards of Mayport, Fla. But the facts remain the same.
Case No. 1—XYZ Co. asked its gas supplier to review gas cylinder pricing for the argon/CO2 mix it uses. Usage had climbed from three to 10 typical Linde-style T, 380-cubic-foot cylinders a week over the past three years.
Following the review, the supplier lowered the price from $29.50 to $26 per cylinder; $3.50 per cylinder x 10 cylinders = $35per week, the equivalent of just over one cylinder for a savings of $1,820 per year. Nice savings; everyone is happy.
Now let's look at some hidden facts. In a standard indoor shop environment, an adequate gas flow rate at the welding gun for GMAW or flux-core welding should be 25 cubic feet per hour (CFH), plus or minus 5. But it is very common to find flow rates at 50 CFH to 70 CFH, in which case half of all the 10 cylinders a week are wasted. Another way of looking at it is using two cylinders to do the job one cylinder should be doing.
Let's do the math. Out of 10 cylinders, five are wasted. The new price of $26per cylinder x five cylinders = $130 a week x 52 weeks = $6,760a year—the price of two brand-new, 400-amp welding power supplies. What would be the company's reaction if the supplier doubled the gas price and none was wasted? Same difference.
Case No. 2—ABC Aluminum Mfg. Co., which fabricates aluminum and stainless steel, uses straight argon at $34 per cylinder and an argon/helium mix at $48 per cylinder. Helium always is premium-priced because of government controls.
The company uses both GMAW and GTAW. The combined processes use 12 argon cylinders a week. If the flow rates are at 50 CFH-plus—the worst-case scenario—six cylinders a week can be written off as waste. Six x $34 = $204 per week x 52 weeks = $10,608 a year—the price of two brand-new, complete 350-amp GTAW packages.
The argon/helium mix has different gas flow requirements because of the density of helium; 40 to 50 CFM is well within the proper range. But if the helium mix flow rates are needlessly maxed out to 70 CFH or higher, another $2,500 to $3,000 easily can be wasted a year. If straight helium is used, as is common for Navy work, 70 CFH is common and generally required per military specification for aluminum GMAW.
Case No. 3—What if five welders use four cylinders each week (20 total) and gas flow rates all exceed 50 CFH? Wasting 10 cylinders a week x 52 weeks = 520 cylinders x $34 each, or $17,680 per year.
I don't doubt for a second there will be an immediate cry of foul from the welders—the gas flow rates are justified to prevent porosity and problems not even associated with the shielding gas properties. Let's evaluate and refute 95 percent of those oppositions. (Why not 100 percent? Welding is no different from any other manufacturing process, so I'll accept 5 percent as having no answer or reasoning.)
Excess gas flow rates at the GMAW gun or GTAW torch isn't the only cause of gas loss. Every connection in the shielding gas supply system is a potential source of loss, from the cylinder shutoff valve and regulator connection to the gas exit at the nozzle.
A very simple test can determine immediately if a severe leak exists. Walk up to any welding system after the welder stops welding and look at the ball in the flow tube. Any reading of the ball location above 0 (zero) indicates gas flow.
Turn off the cylinder handwheel. Does the ball drop at all? If so, it indicates flow. When the welder is not welding, there should be nogas flow.
If the ball does not drop, still pay attention to the cylinder's high-pressure content gauge on the regulator. How quickly does the needle return to 0? Immediately? In a minute or two? An immediate drop indicates a serious leak. Again, let's do the math: a 5-CFH leak for 8 hours a day x five days = 200 cu. ft. of gas x 52 weeks = 10,400 cu. ft. 300 cu. ft. per cylinder, = 34 cylinders at an arbitrary $34 each = $1,156 per year wasted. (The same needle-driftcheck can be performed on the oxygen fuel gas system for the cutting torch.)
Technically, the needle should never drift to 0, even after 24 hours, but let's stay real about things. If the needle drifts to 200 PSI to 300 PSI overnight, I could live with that, but the same drift over an hour is cause for concern.
Look for these potential gas leak sites.
Cylinder packings around the handwheel's on/off valve. A leak here is uncommon, but check for it with a soap spray solution. Notify the supplier if bubbles form, which indicates a leak. Do notmake any adjustments to the cylinder packings.
Cylinder regulator connection to the cylinder valve. If the regulator nut is damaged to the point that it cannot be tightened properly, send it in for repair, and stop using pliers and crescent wrenches to install regulators. Use the proper open-end wrench.
The regulator nipple that seats inside the cylinder valve also could be nicked or gouged to the point it no longer seals pressures up to 2,400 PSI.
Gas hose connections to the regulator outlet. Gas pressure from this point on is low and may not respond to a soap solution to detect leaks. You have to rely on needle drift to indicate if the connection is tight.
Cut, burned, or abraded gas hose from the regulator to the gas solenoid may be visible.
Gas hose connections at the machine or wire feeder solenoid. If the solenoid is working properly, it will close and no gas will flow through it when welding stops. Any needle drift may be caused by leaks from this point back to the cylinder.
There still may be shield gas system leaks to the end of the GMAW gun or GTAW torch nozzle. But they will be a little bit more difficult to detect. The fact is, all these little leaks, singular or accumulated, contribute to the welder's need to increase gas flow at the regulator-flow tube.
Other areas of gas leak concern exist. In the GMAW process, check the gas hose from the outlet of the gas solenoid to the gun plug-in at the wire feeder. Also, the gun plug-in stud (the part that plugs into the feeder) should have two O-rings to seal where the gas enters the gun assembly.
If the GMAW gun nozzle is filled with weld spatter, it needs to be cleaned. (Spatter should not build up in the spray transfer mode.)
In the GTAW process, check the connections of the gas hose from the gas solenoid to the torch adapter block at the power supply output connection. Check the gas hose from the adapter block connection to the torch handle for cuts, burns, and sharp bends, which close off gas flow. O-rings are required at the torch backcap to prevent gas loss. Some torches require seal insulators prior to shield cup installation. (Check the torch parts manual.)
Some GTAW torches have a gas valve at the torch handle that connects directly to the regulator-flow tube. If the gas valve is turned off after welding, the flow tube ball will return to 0; if it doesn't, the gas line has a hole in it. Also, if the gas valve is not turned off after welding, the gas will continue to flow at the rate set at the flow tube. If the gas valve is left on for a length of time, the cylinder slowly will empty.
Another common reason for high gas flow rate is an effort to eliminate porosity. With most porosity problems, more gas flow isn't the solution. In fact, increasing gas flow could make things worse.
What's causing the porosity? Open doors or a fan blowing nearby? Air being discharged by close machinery? Yes, I know how hot it can get welding. Been there, done that! Air-cooled vests that can be worn over a T-shirt and under a welding coat that operate on 3 to 10 PSI from an external air supply are available, along with welding helmets that operate the same. Ship welders encounter temperatures well in excess of 100 degrees F.
A common assumption among many welders is higher gas flow increases weld penetration, so if 25 CFH is good, then 50 or 60 must be better. Wrong; it doesn't work that way.
A word of caution on figuring weld time versus cylinder content: Just because a welder worked for eight hours and had a flow rate of 30 CFH doesn't mean he used 240 CFH of gas. That would be 100 percent productivity, which is impossible. Actual arc-on time equals gas flow time.
Welders stop welding for several reasons. First and foremost, the length of time a welder can carry an arc nonstop is determined by several circumstances, such as repositioning time, moving around the part or table, changing tips, changing out cylinders, clearing possible wire jams, drinking water, and breaks. A welder who can stay under the helmet for 40 minutes an hour is an extremely productive person. Twenty to 30 minutes is the norm. Thirty minutes of arc time = 30 minutes of gas time. So for an eight-hour day, that's four hours' gas time at 30 CFH = 120 cu. ft. of gas. If a welder is changing out a 300-cu.-ft. cylinder daily, something is wrong.
A confusing issue is how to properly compare costs of different cylinders. There is only one practical way—cost per hundred:
Bulk liquid gases will be dealt with another time, but comparison-shopping follows the same principle.
Another wasteful practice (without a price tag) typical in the industry is the failure to identify empty ( MT) cylinders properly before pickup and exchange by the supplier. Talk to anyone in the cylinder-filling business and the discussion of how many full cylinders were returned that week will arise.
Full or partially full cylinders cannot be topped off like the gas tank in your car. They must be bled down to empty before filled. Unless each cylinder is gauged before it is hooked up to the fill manifold, there is no way to know the content status. Gauging each cylinder is too time-consuming and, therefore, will never happen. Time is money.
I must admit, any cylinder wrongfully picked up empty is the sole responsibility of the customer. Empties mustbe located and identified for all those concerned with compressed-gas cylinders at the company, which is required by the Occupational Safety and Health Administration (OSHA) per 29 CFR 1910, Subpart Q.
An industry standard that I have witnessed for more than 30 years is the use of 5-in. steel or plastic rings placed over the cylinder cap of empty cylinders. No mistakes; everyone in the industry knows what that means. Do not write"MT" on the cylinder with a marker; it means nothing. Paying for full and returning full happens all the time and is an excellent example of waste.
Another welding shop economics consideration is cylinder rent, demurrage, or lease (call it what you may). It's that monthly or yearly charge for the use of your supplier's primary asset, cylinders. All suppliers have this charge.
Owning and maintaining compressed-gas cylinders is expensive. A costly mistake most companies that rent cylinders make is to let empties sit around indefinitely. Return empties. Tag them with that 5-in. ring and return them. If you don't want them replaced with a full cylinder, you must meet the driver and let him know or he will exchange it for a full one.
The only other alternative is to purchase the cylinders you require and then they become your property. Food for thought: For a large cylinder, approximately 30 months of rent would pay for the tank; and a smaller (150 cu. ft.) tank could be paid for with 12 to 14 months of rent.