No matter your engineering discipline, there is no substitute for field experience. That was my main takeaway after completing an eight-week assignment in July and August 2020, serving as a field engineer on a 10-inch natural gas pipeline project for a major Midwest utility. I had served as design engineer on the project, which ran 9 miles in length near Traverse City, Michigan. Though I was quite familiar with the details, I quickly came to realize the construction phase often forces adjustments you couldn’t have anticipated while designing from behind a desk.
Here are the first four of my eight key takeaways from this experience that might be helpful for engineers and any other technical specialists who haven’t had the opportunity to see pipeline construction firsthand. As someone only a few years into the pipeline industry, I wish I had known these earlier. I hope they will be helpful as others take on the challenges of pipeline engineering and construction.
1. Outline permitting specifications on plans to keep means and methods open to the contractor.
It is often the case that a contractor will want to construct the project differently than it was designed in order to reduce costs, improve schedule, play to strengths or accommodate on-site equipment. Actual field conditions for pipeline construction projects may be a bit different than anticipated, so permitting restrictions should be included on drawings to provide the contractor maximum flexibility if changes are necessary.
To illustrate the point, the contractor selected for this project chose to revise our plans for the trenchless underground crossings along the pipeline corridor from a conventional bore to a horizontal directional drilling (HDD) technique. For conventional boring, a pit is excavated on each side of a crossing and a boring machine is placed in the entry pit to drill a borehole at the specified depth beneath the feature being crossed. The boring machine continues until a clean borehole is achieved and then the drill stems are replaced with pipe that is then pushed across to complete the trenchless crossing.
With HDD, however, the drilling rig is placed at grade at longer distances from the crossing feature. The drilling commences in an arc until it reaches the minimum depth required for crossing beneath the feature and then emerges at a certain point on the other side, where the pipe is attached to the drill stems and pulled back through the drilled hole.
Most of the road crossings were designed for the conventional bore method based on the minimum depth requirements for each crossing permit. However, a provision allowed the contractor discretion to switch to the HDD method, based on field conditions.
Stating minimum depth constraints for crossings is just one example of how detailing permitting requirements, rather than means and methods, allows the contractor flexibility to work to its strengths.
Though HDD creates more flexibility to adapt to unforeseen subsurface conditions (i.e., the longer drilling distance creates the ability to change direction of the drill head as needed), it did create a need for more pipe with abrasion resistant overcoating (ARO) than originally planned which brings us to our next key takeaway.
2. Assume you will need more ARO pipe than expected and plan to order additional contingency or prepare a field coating plan in advance.
Many pipeline contractors are likely to prefer HDD techniques over conventional boring for small diameter pipe (less than 12-inch). HDD allows the contractor to avoid digging pits on each side of the crossing, allows for more maneuverability of the drill head, and can be completed over greater lengths — sometimes close to a mile.
On this project, when the trenchless crossings transitioned from a conventional bore to HDDs, the drills were lengthened and, in some spots, even combined together to form a longer drill which resulted in a shortage of ARO pipe. We worked around the shortage of ARO by getting approval for a method of field coating that would meet client standards for trenchless crossings. Though field coating resolved our need for more abrasion resistant pipe in this instance, upping the contingency supply for ARO by 20% would have saved time and coordination of a field coating technique. This 20% is project specific and should not be universally applied, though it can be used as a go by in cases where drills are likely to be extended and/or added.
3. Effectively communicating what is shown in a construction drawing is a crucial skill.
There was and always will be a big range of experience and knowledge of pipeline construction among crew members working on the right-of-way, as well as those working in the construction trailer. Some people will have general knowledge spanning all facets of the project and some will be experts in one specific area. Then there are a select few who will be knowledgeable on just about everything. Clear and consistent explanation is vital to getting everyone on the same page, no matter their experience level.
When I arrived on-site, I quickly realized it was important to clearly and consistently explain what was shown on all construction drawings. Nothing compares with face-to-face interaction with a design print in the middle of the table. With some of the team in the field and others back in the office, face to face interaction was not always feasible and was made even more unlikely last summer with COVID-19. For this project, I frequently found myself highlighting or circling items on a drawing set, then texting a photo of the markup with the drawing number to whomever I needed to coordinate with and then calling them to discuss. This combination — of the photo, the drawing number, and explanation of how the photo fit into the station or pipeline — allowed me to communicate effectively with team members of all levels. Being able to accurately and clearly describe a particular design feature is crucial, especially if you are not able to discuss in person.
4. Expect ideas from the contractor on how to achieve efficiencies.
Pipeline contractors are hired for their construction experience and familiarity with projects of similar size and scope. Based on this familiarity, pipeline contractors are well-versed in pipeline installation and can help identify efficiencies or limitations that may not be obvious to those lacking construction experience.
During our design phase, we conservatively assumed that most of the smaller bends in piping — 22 degrees or less — would be bent in the field while those with larger degree angles would be fabricated in advance through a heat-induction process at a manufacturing facility. However, since our pipe was only 10 inches in diameter, the contractor was able to increase the range up to 25 degrees for field bends. This helped minimize the cost and the time it would take to identify the appropriate bend and transport it from the yard to the pipeline section where it was needed.
For this project we chose to order induction bends for all changes in direction rather than elbows to achieve a 5D bend radius and piggability. Induction bending is a process that involves applying heat to the sections of pipe that will be bent, then applying pressure with specialized equipment in a controlled environment to bend the hot metal to a precise angle specified. This technique prevents excessive wall thinning or other stresses on the steel pipe and results in much greater control to produce accurate angles. Field bending, by contrast, is performed with no heat applied to the steel pipe and is typically completed at the location where it will be installed. On this project, we demonstrated that the angles of cold bends performed in the field could be increased slightly without diminishing the pipe strength and meeting design requirements.
The lesson learned in this instance was not to be as conservative with the maximum angle that could be field bent and to rely on this method when deemed appropriate rather than jumping to more costly induction bends in advance. Sections of pipe that were bent in the field saved time and expense with better safety outcomes. In the future, it should be reasonable to specify more field bends at angles that can be completed successfully on-site pending client approval.
This project, key to providing consistent service to nearby communities, saw geographical challenges and communications adjustments during the COVID-19 pandemic.
