few years ago a friend and I were on a road trip exploring Alaska, somewhere in the vicinity of the Denali Highway. At some point we saw a side road, pulled onto it, got out to walk for a while, and stumbled across one of the locations where the Trans Alaska Pipeline System (TAPS) transitions from above to below ground.

As we walked next to the pipeline, taking a moment to appreciate our first encounter with an iconic piece of infrastructure, I wondered why it would be buried there, in that particular place. To my untrained eye, there weren’t any immediate answers.

Of course, when it came to constructing TAPS, there were plenty of trained eyes inspecting every decision about the pipeline’s design and construction. And over the nearly forty-five years since TAPS was completed, those and other expert eyes have been guiding the implementation of a multitude of pipelines across the state, utilizing best practices learned from TAPS and innovating new solutions to meet the needs of Alaska’s oil, gas, and mining projects.

For most of those projects, the engineering firm of choice is Michael Baker International. “There aren’t too many North Slope pipeline projects that we haven’t had a hand in,” says Chief Pipeline Engineer Paul Carson, who’s been with Michael Baker for twenty-five years and worked for Alyeska Pipeline Service Company before that. “There were a couple where we didn’t actually do the design, but they brought us in for value engineering.”

“Our first North Slope project in Alaska, other than TAPS and prospective gasline projects, was the Alpine project—we were the engineers of record for that,” adds Keith Meyer, the company’s Arctic Pipeline Technical Authority; he was the first employee in Michael Baker’s Anchorage office when it opened to work on the then-proposed Trans Alaska Gas System.

Particularly in Alaska, with the 800-mile TAPS and several proposed major gasline projects over the years, the word “pipeline” invokes images of transporting oil and gas. But pipe is used to transport liquids and gasses for all kinds of applications like sewage systems or natural gas distribution to residences.

So when is it pipe, and when is it a pipeline?

There’s no universal delineation. Scott Lust, senior pipeline engineer at Michael Baker, says that if he had to pick a simple definition, in his mind it’s a pipeline when the contents are under pressure, while Senior Vice President Jeff Baker conceptualizes pipelines as systems that move a product or commodity.

But Lust and Baker are both speaking to the fact that a pipeline’s contents, purpose, and location affect the terms applied to it.

Carson gives the example of “[non-federally regulated] infield lines, where they are either taking fluid from a well pad to a processing facility or going from the processing facility out for reinjection.” He considers them transmission lines, though others might call them distribution lines, “or some of them might be considered gathering lines,” he says.

“There are some distinctions in nomenclature and definition which hinge on federal regulations, so we are careful when we’re talking about what we call a DOT line, which is going to be federally regulated… A lot of the infield lines, we don’t use the same terms per se because we don’t want to get anyone confused.”

At Michael Baker, “We work almost exclusively under federal mandated code requirements, and they describe the pipelines that we usually concentrate on as transmission pipelines, and that’s in opposition to distribution pipelines,” explains Meyer. Distribution refers primarily to getting a liquid or gas to its end user, like a residence or business. “We’re more focused on transmitting the product, whether it be natural gas or some hazardous liquid, from the place of origin to the point where it starts being distributed.”

Long before construction or operations, pipelines need to start with solid design. And while the evolution of technology has changed certain aspects of the design process, it hasn’t necessarily changed the results. “We get to do a lot more analysis because we’ve got much more sophisticated tools these days,” says Lust. “That said, when you look at TAPS, they were able to design it with slide rules and Fortran.” Fortran is a general-purpose, compiled imperative programming language which, at the time, utilized a punch card system to input data for analysis.

This was the system that engineers used to design TAPS, including determining how to account for the event of a major earthquake. Where the pipeline crosses over the Denali fault, for example, it sits on top of approximately 20- to 30-foot beams; in the event of a quake, the beams move with the earth and the pipeline rides on top of them, remaining in place.

This design was put to the test in 2002 by a 7.9 magnitude quake that ruptured three faults, including the Denali fault. Meyer and Carson were in Anchorage at Carson’s birthday party when Alyeska Pipeline Service Co. contacted them, requesting their presence on site. “We said, ‘We’ll be up first thing tomorrow,’ and there was a little silence on the phone and they said, “No, Keith, you don’t understand. We need you now,’” Meyers says.

So Meyer and Carson traveled to the site: “It was amazing,” Meyer recalls. “You could see where the fault occurred along the pipeline, and it occurred almost exactly where we predicted it.”

The pipeline performed beautifully.

“We went through and reanalyzed all of those faults,” Lust says, “And the thing that was interesting was we came up with the same results. The answer didn’t change. The tools we used were different, but what they’d done back in the late ‘60s—that was the answer.”

“Math is math,” Baker adds with a laugh.

The industry standard pipe stress program that Michael Baker continues to use today is the one that was originally developed for TAPS. “It turned into a commercial program which pretty much everybody knows and most everybody uses for pipelines and piping,” Carson explains.

TAPS remains an 800-mile example of quality engineering and still informs pipeline construction today, but the industry has continued to further refine pipeline design. In the early days of construction at Prudhoe Bay, many pipelines were constructed with “hat loops,” where the pipe would bend into a rectangular shape with four bends in it. Today, “we can accomplish the same goals with two bends, where you just make a Z loop,” explains Lust. “You still allow for the pipe to flex, but it gets rid of two bends, it gets rid of four welds, and all of the dollar costs associated with those additional welds and bends.

“We [also] got rid of some remote valves on the North Slope,” he continues. “It only works because of the North Slope geometry: it’s flat.”

Traditionally valves are installed in a pipeline to create a shutoff point for maintenance or emergencies. However, valves have leak points, so a pipeline has fewer points of potential failure without them. Instead of installing valves, Michael Baker played a significant role in developing vertical loop design. “[A vertical loop] becomes the highest point of the line, it pulls a vacuum, and it gets rid of the valve,” Lust explains. “Piping that leaks the least is welded pipe, and if you can make a vertical loop out of welded pipe, you now have a valve that doesn’t leak. It only works for liquid lines, but that’s a huge deal, and it’s been used on the Slope where they can.”

“All of these refinements have been directed toward lowering the cost of construction and materials for installing the pipelines,” says Construction/Estimating Manager W.P. (Wes) Nason. “Even if you have to make a 50-foot loop, it’s still cheaper in the long run than sticking in all these valves,” Lust adds. “And every valve you put in you need to maintain.”

“One North Slope-specific issue on the above ground pipelines is wind induced vibration, or WIV. TAPS was not susceptible to it—it’s big, it’s heavy, it doesn’t get excited too much by the wind—but some of our smaller diameter pipelines on the Slope do get excited and can experience some problems if not taken care of,” says Meyer.

“It’s a windy place,” says Baker. “I think of wind before I think of cold when I think of the North Slope.”

The lack of trees, hills, or mountains on the North Slope means there’s nothing to interfere with the wind. One potential solution is to realign the pipeline, though that often isn’t practical: it needs to go where it needs to go.

The more typical solution is a tuned vibration absorber. One version is a kind of ball that hangs off the pipe, another resembles a hammer and might be on top of or suspended from the pipeline. Whatever the shape, they help prevent steady wind from vibrating the pipe. “It’s not high winds that are causing problems, it’s the one that are five to eight miles an hour: very consistent, always blowing,” says Lust.

“It’s not that the wind blows hard enough to damage the pipe directly—in time you get fatigue in the metal if it keeps doing it over and over,” Baker explains.

“Technology and evolving awareness of environmental influences have also affected construction,” Meyer says. “One of the most successful evolutions for construction is horizontal directional drilling [HDD] under rivers. We don’t often dig up rivers anymore if we can drill under them. We did one under the Colville River for the Alpine project—it was pretty innovative for the North Slope at the time. Now HDD is much more accepted and commonplace.”

Even solutions as simple as pipe coatings have evolved, and continue to do so. “Back in the day, pipelines on the slope weren’t coated. They might have insulation on them,” Carson says. “But now the standard practice is to use fusion bonded epoxy, which is considered one of the best corrosion coatings there is.” He adds the caveat that there are other coating and erosion solutions, but they generally aren’t approved for use on US projects—though that isn’t stopping Michael Baker from trying to adopt them.

“We worked on the AK LNG project, and they had to get a special permit from PHMSA [Pipeline Hazardous Materials Safety Administration] to be able to use what outside the United States is considered the best coating around. PHMSA said: Ok, you need a special permit, because US regulations don’t address this. You’ve got to prove it’s as good or better than what the current regulations allow.” Over time, processes or materials allowed only by special permits are often adopted into federal regulations.

Not surprisingly, there’s no cookie cutter pipeline design.

The alloy of the pipe, pipe diameter, the installation of valves or bends, and other design decisions are all determined project by project to meet industry standards and the needs of the project.

For example, pipe diameters on the North Slope range from 2 to 60 inches. “Gathering lines, which are the lines that come from drill sites into the central processing facilities, and some flow gas or water injection lines—those lines typically are 12 inches to 24 inches in diameter,” says Nason. “The short lines that go from the wells into the manifold buildings on the drill site, those are usually between 4 and 8 inches, depending on what the production is at the particular drill site. And then you have transit lines carrying water, gas, and crude between a field and flow station or between the eastern and western areas of Prudhoe Bay, and those are typically 24 inch to 30 inch diameter range, something like that.”

According to the Michael Baker team, generally speaking a practical minimum size of pipe on the North Slope is 6 inches. North Slope pipelines are constructed above ground due to the permafrost and smaller pipes require more supports because they are not rigid enough to span vertical support member spacings of larger pipes, and vertical support members are expensive to install. So while smaller pipe might be suitable for a task, it’s difficult to justify the economics for long, above ground, small diameter lines unless accompanied by larger pipelines.

The transported material also makes a difference. Nason explains that the Point McIntyre and Endicott fields have highly corrosive crude, “so they made their flow lines out of duplex stainless steels,” a steel alloy that Lust says is “orders of magnitude more expensive per foot” than carbon steel.

Water and sewer lines on the slope are generally constructed with high-density polyethylene (HDPE), which is relatively inexpensive and easy to hook together, and they “don’t need to have the same kind of pressure containment,” Baker says.

In Alaska, another big question is whether to bury a line or not.

“The decision is almost always thermal,” Meyer says.

According to Baker, “If a pipe is above ground, it’s because it needs to be above ground.”

“It’s not anybody’s first choice,” Lust echoes, as it’s more expensive and the pipe is exposed.

“[Burying it] is cheaper and it’s less visible: you don’t see it,” Carson adds.

Permafrost unfortunately forces the issue.

“On the North Slope they tried buried pipelines a time or two or three,” Carson laughs. “The problem you have is most of the pipelines are warm. Putting a warm, insulated pipe in the frozen ground, it’s really hard to make sure that the insulation retains its integrity.” The pipe will lose too much heat.

Pipelines on the North Slope range from 2″ to 60″.

Even worse, it loses that heat into the ground, which needs to remain frozen. “You don’t want it to melt because there’s a lot of ice and you can have what’s known as thaw settlement… Pipelines have a certain strength and they can handle some of it, but if it gets too bad, basically they’re trying to bend too close and they might buckle or break,” Carson says.

TAPS is again a highly visual example of how burying a pipeline is always preferable—when possible. “If you get north of Fairbanks and start going through the rolling hills, on the north side TAPS is above ground, and the minute it breaks over and gets a southern exposure, it dips in, goes through the stream crossing, and then hops back up onto the next hill and is above ground, and then drops back again,” Lust says. “They were doing that because wherever they could bury it, they were sticking it in the ground.”

Since TAPS’ completion it has not had a major spill event, operating smoothly for forty-five years, even as work is ongoing to address changes in throughput.

“Pipelines last,” Meyer says. “With good maintenance pipelines last a very, very long time.”

They work in situations where other transportation solutions simply wouldn’t. Roads and railways have pretty restrictive maximum grades that pipelines don’t share.

For instance: an important aspect of planning a pipeline is actually walking the route, and Lust walked a route for a project on the north side of the Alaska Range. “We had flown over it with fixed wing, and I had flown over it in helicopters, and I rode it on a snowmachine, and when I got on the ground it was like, ‘Holy smokes, this is a lot different than I remember,” he says. “Everything softens terrain until you put boots on the ground.”

Along the route, an area that had been identified as a shadow on aerial photography was, in fact, a 150-foot drop in the terrain. “The angle was as steep as it could possibly be and still grow vegetation,” Lust says. The team had to grab hold of the devils club (luckily with heavy leather gloves) to climb back up the incline. But even that wasn’t enough to discount the route.

“You can go pretty darn steep,” Baker says.

“You can put a pipeline where you can’t put anything else, just about,” Lust adds.

Pipelines are a type of linear construction, and “you can build them with a specialized crew in a moving assembly lines method,” Nason says. “It’s fast-paced, it’s fun, and it’s got a unique sub-culture of construction workers.”

In an area with a steep grade, equipment is moved up or down the hill using a high-line, similar to when the timber industry moves logs up a hill.

“You can do anything on a pipeline if it’s short enough,” Lust says. “If you’ve got a small enough section, you can do just about anything to get it built.”

And that’s good news for the project, the people, and the environment. Pipelines are highly reliable and cost-effective infrastructure, as TAPS has demonstrated. Baker adds, “Pipelines don’t need much maintenance, either.”