No Two Welds Alike…
Syncrude’s Many Challenges at Fort McMurray

By Cheryl Rego

Syncrude Canada Ltd. is the world’s largest producer of crude oil from oil sands. Success is always sweet, and the company’s welders are an essential part of the company’s ability to keep supplying Canadians with its Syncrude Sweet Blend (SSB) of crude oil.

Jim Mitchell knows about the challenges Syncrude’s welders face. He is Syncrude’s Senior Metallurgical Engineer based in Fort McMurray, Alberta and has been seeing the sparks fly for 14 years. He said being an expert in one area is not good enough. “Much of the welding done at site in an operating plant is ‘one-of’. The welders become highly skilled usually in multiple processes. For instance, for pressure equipment, we have a hundred welders who are in our system. Most of them can weld with more than one process,” he said.

8-inch-thick narrow gap weld groove

A regular on-site challenge is the extreme temperatures that are endemic to work in this industry. “You try very hard to avoid actually welding in very cold conditions,” Mitchell said. “Under cold welding temperatures, preventing fracture and ensuring weld quality is difficult.” He said that under most circumstances, the work area will be covered in a tent and heated. “We try to add heat to elevate the temperature of the part we’re welding. We have made very large tents from time to time. That’s called “heating and hoarding.” In extreme cases, a proper weld joint cannot be carried out and a temporary weld fix is used. One example of this is to use stainless weld-filler metal to try and hold a joint together to resist cracking for a while,” he said.

Mitchell said the largest area he has seen put under a “heating and hoarding” procedure was about half an acre. “There was an incident when we had to shut down one of the hydrotreater plants during an emergency in the middle of winter. The entire area was scaffolded, covered up and heated to melt ice and create a safe work environment around damaged equipment. In that case, there was extensive damage but we were only 60 days in executing the repairs and getting the plant back on line,” he said.

If sometimes the task is to make temperatures rise, at other times cooler temperatures are very welcome. Mitchell said that when working in high temperatures, the comfort of the welder is paramount. As well, he said, there are some challenging metallurgical issues. “In effect, we are welding with very high preheats. Here we try to minimize the effect of the heat-affected-zone that could degrade weld properties, especially in low alloy steels base metals. This can be justified technically if you’re making a temporary repair. However, most are not temporary; whenever possible, we want the repair to be permanent,” Mitchell said.

Mitchell said that about 80 per cent of the welding done at Syncrude is in the mine area. Much of this welding is hardfacing and restoration of mining equipment. The remainder is a combination of structure and pressure equipment welding in the three other operating areas of the company.

Testing of weld attachment to clad plate

“The challenges around weld hardfacing are mostly economic. With weld-repairing equipment used for mining, there is the cost of welding added to the down-time cost while the equipment is not in service. We’ve made many improvements in the performance of hardfaced equipment and in the productivity of weld overlay.

When Syncrude started out, the teeth on the dragline buckets would last about eight hours until they lost their shape. The buckets were laid down and the teeth replaced. Then the old teeth would return to the shop to be weld repaired,” Mitchell said. Within the first five years of operation, many improvements were made. “Now we have teeth that last much longer than a few hours. They go several hundred hours, they’re easier to remove and they have the right shape for digging,” he said.

“Another challenge with mining equipment is that they are notoriously prone to fatigue cracking. We have been able to resist failures due to fatigue by weld profiling, using high-strength weld filler metal, or changing the joints completely.”

Mitchell listed three main areas where Syncrude engineers and researchers are working hard to develop better procedures. These are:

• weld overlay and hardfacing materials,
• welding of service-affected base metal, and
• live-line welding.

He said that while some of the research is done at Syncrude, the company uses its extensive industry network to share and gain information.

Weld hardfacing is used to resist high erosion or abrasion to ground engaging equipment. Syncrude’s research on weld overlay applied abrasion resistant materials is largely undertaken in its Edmonton Research Centre in conjunction with Syncrude’s Mining and Extraction Departments. In some cases, the actual research or development component is done outside the company through joint industry-sponsored projects.

Partial shell replacement

In the processing cycle, the ore is dug out of the ground, then taken on trucks to a crusher and then to a screen. The screen is in fact a plate with holes. To keep the crushers and screens lasting longer, both have weld overlay or fused overlay applied to them. Weld overlays are metallic coatings welded directly onto the substrate. The high-heat welding process forms a molecular-level bond with the base metal, essentially alloying the coating to the substrate at the interface. The result is a durable coating with excellent resistance to high-stress gouging wear.

The spray and fuse hardfacing overlay process is a fairly recent development. The fusing process introduces high heat levels into the part, similar to or in excess of brazing temperatures (around 1600-2000°F). Work to be coated must be capable of withstanding high levels of heat without risk of deformation. As with any process where two metals are bonded structurally, metallurgical compatibility must be taken into consideration. Some materials will not interface well with others. Further, coefficients of expansion of the substrate and coating must be similar to avoid cracking and warping as the part cools.

Mitchell said that lately Syncrude has done much to study the use of tungsten carbide as an enhanced hardfacing overlay. A tungsten-carbide-overlayed part can accommodate the most severe wear conditions. It can withstand extreme heat while resisting abrasion. “We are still proving out new developments with tungsten carbide and trying to improve them where possible,” he said. Syncrude’s research with tungsten carbide has expanded to include an industry effort with other companies, and has involved agencies, including the National Research Council, and university research. “We share quite a bit of information and in return get much from these joint industry relationships,” Mitchell said.

Repair weld stainless steel vessel internal component

Welding of service-affected materials is another challenge to Syncrude’s operations. In some cases, the materials being welded have been altered. The most common of these degradations are corrosion, hydrogen embrittlement, and high-temperature service all of which lead to a number of structural changes within the material. “Normal welding practices don’t apply,” explained Mitchell. “You need to understand the material and the damage mechanism. When welding is required, the procedure can become a ‘one-of’ exercise – every one of these is different.”

Mitchell said it is not hard to find examples of challenges with service-affected materials. “We have pressure vessels that are 25-plus-years old. One example is welding of low alloy steels that have been in high-temperature service for that length of time. The properties of the steel are altered to the point where it would no longer meet the original material’s specification. Weld repair would need to take this into account, and in most cases the weld requirement of the original code of construction cannot be followed.”

Original construction of Syncrude’s plant required that some steels meet toughness testing done at -50°F. Back then, some steel manufacturers met this by increasing the manganese content to the maximum allowed, with other elements like carbon also being on the high side. That greatly increased the carbon equivalent of these steels, and if you apply the normal welding process you enhance the threat of cold cracking,” he said. High-toughness steels can now be obtained at the low end for carbon equivalents, and Mitchell said that has worked to their favour.

Another challenge occurs if the material has been thinned due to corrosion or erosion. Mitchell said that, in such a case, surface preparation becomes important and sandblasting or grinding is done. “In the case where corroded equipment is charged with hydrogen, preweld processes like thermal degassing (bake out) or elevated preheats are used.” However, he said that care must be taken with these processes. “You have to be careful with preheat depending on the welding used. Some hydrogen still in the base metal can migrate towards the weld if the preheat is too high. Too much hydrogen can result in cracking. In critical applications, very low hydrogen welding processes are used. Welding is best performed at as low a preheat as can be tolerated. Also, we allow the welding temperature to be maintained for a period of time, usually two hours,” he said. Several of these techniques are prescribed in the National Board Inspection Code for in-service equipment.

The third area of difficulty is related to maintenance welding, also known as live-line welding, which is maintenance to equipment while it is in service. “When a piece of equipment is becoming critically thin, we will often attach another pressure envelope around it. We refer to this as a leak box, which is designed to be the same as a pressure vessel. Eventually the equipment may develop a hole, but we can continue to operate. We have this on everything from steam systems to plant process piping. Attaching leak boxes requires the utmost design and welder skill. The welder needs to control the depth penetration while at times coping with high weld preheat temperatures or welding while the equipment is vibrating,” Mitchell said. “For example, if the steam line is leaking and we feel we can safely install a leak box, we’ll use our shop facilities to prefabricate the leak box. It is usually installed in two halves. These halves are fitted over the leak. The steam or gases that are escaping are drawn off through a nozzle and valve. The leak box is welded shut, and the valve is then closed.”

Each day brings a new welding challenge. Mitchell has many stories to tell, but one stands out among them. “During the repair of a steam methane reform furnace outlet piping, we found that when we tried to weld it back together it cracked immediately. This had been in service for three years prior to the repair. The high-alloy cast fittings had become metallurgically altered and welding developed liquation cracking. What happens is that, during welding, part of the base metal adjacent to the weld zone melts, yawns open, and leaves a crack. When the weld solidifies, the weld is sound but the adjacent material is cracked,” he explained. “We have a metallurgical lab at site and were able to detect this condition within about two days. They [the lab] came up with a heat treatment procedure that would ‘condition’ the end of the piping we were trying to weld. At the time (1991), we didn’t know what was causing this liquation cracking. Our site metallurgical lab was a great benefit. The industry has since figured it out, but we were amongst the first to report it with these alloys. We have since shared that information with many in the industry.”

Listening to Mitchell, you would have no doubt that welding at Syncrude is not for the faint of heart, nor for those interested in routine work. Hiring welders is difficult, as the company suffers the same welder shortage that plagues most industries. A partnership with Keyano College in Fort McMurray has been established to test welder performance, allowing welders to practice with different processes and techniques.

For those welders already at Syncrude, daily challenges mean they can look forward to learning something new everyday.