Stress Relieving with Induction Heating Cuts Out the Middle Man
Under the guidelines of ASME Section VIII Division 1, any pressure vessel exceeding one-and-a-half inches in thickness is required to undergo post-weld stress relief. Depending on the thickness of the vessel, this typically involves ramping up its temperature to approximately 1,100 degrees Fahrenheit.
“Our choices were to ship that product out to a third party that has an oven able to do the work,” says Murray. “In Northern Ohio, there’s only a couple of places that have the ability to do that. One of the first things we started looking at was just how can we do this process in house?”
The company began looking at ovens of their own, until they were introduced to the induction heating process as made possible by the Miller ProHeat™ 35 induction heating system. With an induction heating system, heat is created electromagnetically in the part by placing it in an alternating magnetic field created by liquid-cooled induction heating cables. The induction cables are wrapped around the part, or on the part, and do not heat up themselves, but create eddy currents inside the part that generate heat.
“We’re able to basically pinpoint the heat where it’s needed and not waste energy heating the rest of the vessel,” says Murray. “These vessels weigh anywhere from 5,000 pounds up to 10,000 pounds. The oven technology forces us to heat the whole vessel where the Miller product can just pinpoint that to those areas. So we decided to buy the product, bring it in and start implementing it. It saved us a tremendous amount of time in just trucking and handling the product. The biggest thing is having control over our own product. Now it’s not going out to a third party vendor. We’re in control of the process doing the stress relief. With the recorder on it and the way we set up… it’s particularly easy to meet the ASME code requirements. It’s been a big advantage.”
The ProHeat 35 gives Pride of the Hills the control to ramp up the temperature as fast or as slow as dictated by the code. Similarly, after spending the prescribed amount of time at its soak temperature, the system can ramp down temperature to code requirements. This overall process can last 5 to 12 hours, depending on the thickness of the vessel. Having that control, and being able to document the entire process through a digital recorder, is important to the quality control process and, ultimately, in documenting to the customer that the part was fabricated properly.
“Our quality control department looks at it and then our authorized inspector looks at it, and then – as on all of our equipment – we send our customer an as-built document (that includes this data),” says Murray.
While quality is paramount, the ability to do it all in house and not rely on third-party vendors has helped shorten lead times noticeably. Aside from the six hours of trucking and handling previously associated with getting a vessel to the oven, Murray also took into account the labor, diesel fuel, truck wear and tear, and being at the mercy of the oven owner’s schedule which could add unnecessary downtime to the process. All together, it added up to a smart change.
“We were literally able to cut at least a couple of days (out of the process),” says Murray.
Change in welding process increases production
Pride of the Hills Manufacturing of Big Prairie, Ohio is largely sustained by what sits hundreds and thousands of feet beneath those hills: shale gas. Set in the heart of Marcellus and Utica Shale country, Pride of the Hills has grown with the region’s shale gas production boom. As a manufacturer of oil and gas production equipment, the company has grown and evolved with increased production levels, locally and nationwide.
There was once a time when a great shale well in the area produced 100,000 cubic feet of natural gas per day. A good shale well now produces 60 million cubic feet per day. Pride of the Hills has responded in kind, moving from smaller, low-pressure equipment to the larger, higher pressure systems it now takes to operate a shale gas well.
With increasing production comes an expedited demand for Pride of the Hills’ products: production equipment that sits at the head of the well and separates the oil, gas and water and turns it into a saleable product. These systems are complicated networks of pressure vessels and high-pressure piping. To meet that demand, the company has taken welding processes that are conventional by industry standards (TIG root, Stick hot and cover passes) and changed them to solid wire MIG applications (Regulated Metal Deposition (RMD™) and Pulsed MIG) to significantly increase production and meet customer demand. On a micro scale, that means taking a 2-hour welding process down to 20 minutes and reducing test failure rates on its sand separators down to almost zero. On a macro scale, it means producing an entire system from scratch in the time it previously took just to do the welding.
“We’ve been able to reduce our man hours to produce that same product at the same high quality by using newer technology in a controlled environment, and have that accepted by people that have some real stringent standards,” says Curt Murray Jr., vice president of Pride of the Hills Manufacturing and president/founder of Grace Automation.
High Pressures at the Head of the Well
The gas stream that comes out of a shale gas well does so at between 3,000 and 6,000 pounds of pressure. That stream then goes through a sand separator rated between 5,000 and 6,000 pounds that allows the solids to settle out of the oil, water and gas stream. That stream is then depressurized, which causes rapid cooling, dropping in temperature by as much as 150 degrees. That stream is then reheated and brought back through the separator, removing the fluids and sending the natural gas down the line. Pride of the Hills also designs systems that can take the bulk liquid remains and turn the oil into a stable, saleable product.
“Our challenges are that we’re dealing with high pressures, high volumes of dirty product that we have to clean, regulate, produce safely, monitor and put down into a sales line into a place where it can be used for your home or my factory or trucked off someplace.”
Dealing with the Pressure
Pride of the Hills’ products are extensively regulated due to the volatility of the oil and gas extraction process. Piping is typically constructed of an A/SA106 grade B or grade C carbon steel, while pressure vessels are typically built of SA516 grade 70 material. The company’s work is regulated under codes from the American Petroleum Institute (API - numerous) and the American Society of Mechanical Engineers (ASME – B31.3), as well as the strict requirements of each customer. All welding processes must be tested and proven to meet the quality of each code.
Murray recounts the recent process with one of his primary customers, Shell, in examining ways to shorten product lead times without actually expanding his facilities (although the company is also physically expanding as well). Much of the work performed required conventional methods: TIG welding in the root pass and then performing follow-up passes with Stick welding. What Murray and his team proposed was performing root passes with the RMD process and then transitioning to a Pulsed MIG process on the remaining passes.
“We had to weld test coupons, pull tensiles, acid etch it and such to prove to them that it was as high a quality weld as what they were getting with the (previous processes),” says Murray. “And it wasn’t without challenges because a large company would just as well stay with the standards that they were comfortable with. But because of their need for equipment and their delivery times, we were able to convince them that we can do it in another process that will give you the quality that you need to feel safe, but we can also meet your timelines.”
Tests proved to Shell that these new processes met their quality requirements and would help significantly shorten lead times on the products they needed from Pride of the Hills.
“When you start looking at the mechanicals of a weld,” says Murray, “it has very much to do with the strength of the material you’re welding with, so when we compare a similar wire to a similar rod, the mechanicals are going to be very similar. So even though we’re going to be depositing them a little differently, inevitably the mechanicals end up very similar. So the quality of the weld, the mechanics of the weld and everything looked very similar to what their expectations were (compared to other types of metal transfer).”
The Evolution of Welding Processes
Pride of the Hills moved forward and replaced TIG welding of the root with RMD, relying on the Miller PipeWorx Welding System as its primary welding power source. RMD is a modified short-circuit MIG process where the welding system anticipates and controls the short circuit, then reduces welding current to create a consistent metal transfer. Precisely controlled metal transfer provides uniform droplet deposition, making it easier for the welder to control the puddle. The smooth metal transfer also compensates for high-low misalignment between pipe sections and creates more consistent root reinforcement on the inside of the pipe (than other short-circuit MIG processes). The process also maintains a consistent arc length regardless of electrode stick-out. It compensates for operators that have problems holding a constant stick-out, and it enables a better view of the weld puddle – making the process much easier to learn than TIG welding.
“When you start TIG welding,” says Murray, “your deposition rates are desperately low. It’s a great weld, but we’re hand feeding one drop of metal at a time into the root pass. It also takes a highly skilled person to do that… now, instead of manually feeding a filler metal, it’s being fed automatically by the machine. Now, instead of us using a foot pedal to control the heat, we have a truly adaptive (power source) that, as we change our tip-to-work distance or we move around a little bit like we do as humans, the (power source) is automatically adjusting to those changes for us.”
For fill and cap passes, the company has transitioned from Stick welding to Pulsed MIG welding. Pulsed MIG provides easy puddle control for both in-position and out-of-position welding, helping to reduce training time. The process also improves fusion and fill at the toe of the weld, which leads to faster travel speeds and higher deposition rates. Less heat input also reduces interpass cooling time, which improves weld cycle times and helps retain the mechanical properties of the pipe.
“It allows us to actually put in a higher deposition rate then we can with the Stick,” says Murray. “And at the end of that pass, your Stick welder is going to have to stop, he’s going to have to chip off the slag that he just placed, he’s going to have to back grind that weld to get it clean and prepped to put the next weld on top of it. Where our welder today uses a pulse spray, he may have a little bit of a silicon puddle or a little bit of impurity on the top that he can just run a wire wheel on, so it’s really a quick clean-up.”
Both processes have also allowed the company to standardize largely on one wire type (ER70S-6) and one gas type (90 percent argon/10 percent CO2), further simplifying inventory and training. The company has even outfitted a robotic cell with a Miller Auto-Access® system capable of performing both processes. Murray believes RMD and Pulsed MIG welding have helped spur productivity quantifiable improvements.
“We’re able to bring it into the shop, get it into a controlled environment where we can use a hard wire gas-shielded process and provide just as high quality of weld because we are in the controlled environment,” says Murray. “And we can take that hour-and-a-half or two hour process (on one joint) and reduce it using a hand-held mechanized welder to something around 20 minutes. And then we also can take (another) step there and put it over on our robot using similar welding processes and take it down to 10 or 15 minutes.”
Those improvements are impressive on a per-joint basis, but the true benefit of reduced lead times for its customers comes into perspective when you consider the entire process that goes into creating one gas processing unit.
“If you take the 400 man hours of work (that goes into one system), we probably have about 150 hours of it that’s welding, or preparation for welding,” says Murray. “If we took that and did it with a TIG and Stick process, we estimated that we’d probably take that (welding portion) up to about the 400 hours of time that it’s (currently) taking us to produce the whole unit, and still have another 250 hours (of additional work) to put into the unit.”
That puts total production time at 400 hours with RMD and Pulsed MIG, and approximately 650 hours with TIG and Stick — a 250 hour savings, or more than a 1/3 cut in production time.
RMD Nearly Perfects Testing Rates on Pressure Vessels
One of the key components of the systems Pride of the Hills manufactures is the actual sand separator, which is a pressure vessel that ranges in thickness from one-and-a-half to four inches, depending on the model. The company previously relied on a standard short arc MIG process to put in the root pass and two hot passes. This is done to build up the root with enough material to support a submerged arc, or sub-arc, welding process that completes the rest of the joint. The sub-arc process takes approximately 8 hours as a dual-headed system welds up both heads simultaneously.
Fit-up and root pass quality is critical as each vessel is 100 percent x-rayed. If there is a flaw, such as lack of fusion in the root, all four inches of weld have to be gouged out and redone – a major setback in productivity. While Murray says his welders had high passing rates with the established process – in the mid to upper 90 percent range – he thought it worthy to implement RMD in the root pass and Pulsed MIG for the hot passes to see if they could get that rejection rate as close to zero as possible.
In this application, RMD and Pulsed MIG didn’t increase productivity in terms of faster production rates, but it did succeed in Murray’s goal of reducing rejection rates and rework.
“(RMD), in that application, is a quality gain for us,” says Murray. “Where we gain efficiency is a lack of failures. The failure rate has just gone to near zero. When we’re putting a three-and-a-half or four-inch weld on top of that root pass, if we make a mistake in the root, we’re air arcing for a couple of hours to get down to fix it, and then we have several hours of filling that back up by hand. It’s just so important that we make that good first root pass.”
The PipeWorx Advantage
The bulk of the manual welding performed at Pride of the Hills in these applications is done with the PipeWorx Welding System. PipeWorx is a multiprocess power source capable of performing RMD and Pulsed MIG welding, and offers a number of features that simplify the welding processes and help new welders learn faster. This includes quick process changeover with no need to manually switch polarity or cables and hoses between processes. Welders can also trigger through pre-set programs while at the welding joint, eliminating downtime associated with walking back and re-setting the machine.
“What we found with the PipeWorx, and why we gravitated towards it is its ease of setup,” says Murray. “To be able to walk up to the machine, flip open the front cover and actually just push a couple of buttons to select the wire, the gas, the type of process we want to use, and then be able to pre-program several amperage and voltage settings that we can just trigger through as we go from pass to pass. One of the big advantages was just the ease of use.”
That flexibility in changing weld settings by simply triggering the gun is particularly helpful to his workers.
“When we get into our hot passes and our cover passes, when we’re moving from a three-inch to a four-inch, to a six-inch or maybe a ten-inch thick material, different widths of welds as we get up higher, they really like that they can just trigger from one program to another. We don’t have to go back to the machine and turn knobs.”
The PipeWorx also makes these processes considerably easier to learn – important as, with most in the manufacturing industry, Pride of the Hills is challenged with finding skilled labor in the region. One of the ways it does this is through adaptive technology. The power source senses changes in variables such as tip-to-work distance and welder movement to adjust weld parameters and ensure optimal weld conditions and quality.
“What happens is, if I’m running an (older welding power source) that’s not as smart, per se, and I’m depositing metal and my gap changes a little bit, goes in or out, I’m forced to slow down, speed up, change my tip-to-work distance, trying to make up for that change in the weld gap. Now the machine has the ability to sense that something is changing here… so now the machine is adapting to those changes versus us having to train the person to adapt to it.”
Ultimately, Murray finds it’s the right power source for the job.
“When your workers are getting great quality results and they’re saying, this is the one we want, that’s where you go. We try to put them in the best position to succeed as possible, and if you have a machine that helps you do that, you want to use that machine.”