Lessons Learned In Reducing Shielding Gas Costs
Facing the harsh realities of our current economy can be challenging. Working in an industry where every penny counts, it is extremely important for managers, engineers and welders to examine all processes to determine where potential cost savings are and implement necessary changes as quickly as possible. Looking at the gas equipment side of welding applications can yield some significant cost savings with very little investment. Furthermore, making a careful analysis of shielding gas equipment can yield some great rewards.
Know Your Process
First of all, know the process intimately. How much gas is required to produce an adequate weld? Many welding processes are extremely wasteful when it comes to setting the shielding gas flow rates. The cost of shielding gas is one of the most expensive elements in any welding process. How difficult is it for welders to set higher flows than needed or recommended? Most equipment manufacturers offer flow control equipment or accessories which can be set to a maximum limit so that excessive flow rates cannot be used.
Furthermore, shielding gas pressures and flows that are too high make the gas turbulent, drawing oxides and nitrides into the weld. Most welders as well as welding application engineers are still not familiar with inert gas saving devices on the market such as the Harris Inert Gas Guard® (IGG) which can save gas by eliminating the gas surge associated with each trigger pull. These devices have been around for at least 20 years, but they never seem to get much attention until there is a cost-saving crunch or economic downturn where there is an effort to eliminate waste and expose hidden costs.
How It Works
Their principle of operation is very simple; reduce the line pressure to eliminate the gas surge caused by the build-up in pressure while the process is idle. Most flow control equipment used with shielding gases, whether from a cylinder or a bulk system, is designed to operate at a nominal inlet pressure of about 20 to 30 psig. Applications using pure carbon dioxide may operate at pressures up to 50 psig. This means that every time the welding torch is activated, there is an initial pressure of 20 to 30, or 50 psig at the welding nozzle. This high static pressure causes a large amount of gas to exit the nozzle when the torch trigger is hit.
To get a more quantitative picture of this, let’s assume the following: 1) the welding process requires 35 scfh of argon, 2) the flowmeter installed upstream and connected to the welding machine has a calibration pressure of 20 psig. Through a typical gas diffuser, at these settings, initial flow rates can easily reach or even exceed 180 scfh of argon. Although the flow rate quickly drops as the line pressure decays downward toward atmospheric conditions, this still represents more than 5 times the flow rate needed for the welding application. This happens at every trigger pull. It is not uncommon for some applications to have 200 to 300 trigger pulls per hour exponentially increasing the amount of wasted gas.
Get the Numbers
Some calculations are necessary to understand and realize how much the potential gas savings can be. The Harris Products Group has introduced a web-based program to identify important parameters and aid in the calculation of shielding gas loss.
The program can be found here. Users will need to collect some information before getting started. The program requires that the user input the following:
- Inside diameter and the length of the pipe or hose which goes from the flowmeter to the wirefeeder
- Static pressure build-up; this is typically the pressure printed on the ball and tube flowmeter. It will normally not be higher than 50 psig (for flowgauge regulators, a physical measurement may need to be taken)
- What is the pressure in the line while the gas is flowing; we should assume that this pressure is very low around 3 or 4 psig
- Approximately how many trigger pulls per hour in the process
- The cost of 100 cubic feet of shielding gas (at the time of this writing, argon was retail $21.33 per 100 cubic feet from a local supplier)
The Harris program gives the user an estimate of the amount of gas wasted for one welding station. This calculator can be used for each station to get a clearer picture of how much gas is being lost in the entire facility. As an example, see the following variables below with the estimated yearly savings if a Harris gas saver (#3000328) is used.
- Length of hose – 12 ft
- I.D. of hose – 3/16”
- Static line pressure – 20 psig
- Flowing line pressure – 3 psig
- Number of trigger pulls per hour - 175
- Cost of 100 cubic feet of gas - $21.33
- Yearly savings = $218.76
Typical Setup with Harris flowmeter regulator and Inert Gas Guard installed on the outlet.
The retail cost of the Harris gas saver is significantly less than the estimated yearly savings and, for these parameters, will yield an average rate of return around 115% per welding station over three years. The calculator program does not take into effect leaks in the system or variable inputs which are not accurately obtained. Gas leakages in a large piped facility can be numerous and more times than not go unnoticed or ignored until gas costs are evaluated and efforts to rein in costs are explored.
Beware of manufacturers who market small in-line restricted orifices as shielding gas savers. These devices only result in a pressure drop across the orifice. During static conditions, pressures will still climb higher than needed and there will only be a token amount of gas savings achieved. Also, if these devices are not installed at the right location, then there may not be any appreciable gas savings. The only way to effectively eliminate shielding gas surge is to introduce a pressure regulating device into the gas system.
After taking care of the immediate need to save shielding gas at every welding station, managers and engineers should then turn their eye to look at deficiencies in the entire facility. Compressed gas equipment, such as flowmeters, regulators, hoses, quick connects, etc., that are commonly used to control the pressure and flow of shielding gases in GMAW and GTAW processes, can also be a source of gas leakage if not maintained and replaced at regular intervals. Preventive maintenance procedures should also be in place to insure that equipment is not used past its expected life span. Contact the manufacturer regarding how often equipment should be inspected and/or replaced.
How long should gas pressure and flow control equipment function properly under normal service conditions? What is considered a harsh service environment? What tests should be included on preventive maintenance charts? These are questions that manufacturers are constantly asked by consumers concerning the service and life expectancy of compressed gas equipment. Unfortunately, the answers are varied and somewhat complicated.
Consider customer “A”. This customer uses one cylinder of argon per month, pressurizing the flowmeter once a week to weld for about 20 minutes inside a building where temperature, humidity and other environmental factors are controlled. This regulator may last 10 years or more without refurbishing or replacing any major components. In fact, The Harris Products Group frequently hears from customers who have used the same Harris regulator since the 1940’s with no problems, however, these are extreme cases. Contrast that with customer “B” who uses an argon/carbon dioxide flowmeter regulator several hours a day on an oilrig off the Gulf Coast of Mississippi. Because of the salty air and harsh environment in and around an oilrig, this regulator may need a major overhaul or replacing in as little as three months. Because the applications for compressed gas equipment is so varied, the life expectancy is varied and proportional to the gas service and the environment in which the device is used.
All compressed gas systems including pipelines, equipment, hoses and all fittings should be routinely checked for leaks to insure system integrity. For flowmeters, regulators, hoses and fittings commercially available liquid leak detectors are most efficient in checking for any escape of gas to the atmosphere. For pipelines, it may be more practical to perform a static line test with a pressure gauge at various points to determine if leakages exist. The most important point is that these gas systems cannot be ignored and are often the cause of excessive shielding gas costs. Tests for leakage in gas regulators and hoses should be done at every setup or, at least twice per week while tests on pipelines should be performed once a month.
Cost savings on shielding gas can be achieved if these steps are implemented and practical preventive maintenance programs are put in place.
David Gailey is the manager for Specialty Products for The Harris Products Group, A Lincoln Electric Co. He has been with Harris for 27 years and served as past chairman of the CGA Industrial Gas Apparatus Committee