Nearly every construction project is likely to face unexpected situations and changes that were not anticipated during the design phase. Field assignments for pipeline construction in particular can offer valuable lessons.
Though the types of challenges and situations that arise on pipeline projects may be unique, there is no question that changes are likely to occur in the field on any project. It is prudent to prepare for the unexpected.
Here are the remaining four key takeaways from my recent experience on a field assignment for the construction of a nine-mile natural gas transmission pipeline near Traverse City, Michigan.
1. Pipe installation via horizontal directional drilling (HDD) can be either the most efficient or the most time-consuming method to install pipe.
HDD is becoming the preferred method for trenchless underground crossings, though it does come with certain risks. In this case, one of those risks was an inadvertent return of drilling fluid (aka frac-out) that escaped from the proposed drill path and surfaced on the ground.
HDD is a method of pressurized drilling that involves the use of a bentonite-mixed drilling mud. This mixture expands with water to maintain pressure, then solidifies in the hole to create a fixed pathway for the pipe to be installed. However, when the drill path encounters a fissure in the rock or finds another pathway to the surface, fluids can escape into the surrounding voids. When the drilling fluid makes it to the surface, it becomes an inadvertent return. Not only does drill mud loss cause the drill to lose pressure, it also poses the potential to leak drilling mud into surrounding areas, potentially coming into contact with groundwater or pushing it towards the surface where it could encounter a wetland area.
The inadvertent return we encountered resulted in a delay while environmental authorities were contacted, and remediation operations ensued. When we were able to restart drilling operations, we (the drilling contractor, the construction contractor, the client and the engineering design team) determined the drill path should be 20 feet deeper than the original proposed path to maintain higher pressures within the bore hole and to avoid the unstable rock layer that we had previously tried to pass though.
Though it is impossible to guard against every possibility, I learned it is best to expect the unexpected and order additional soil sampling and geotechnical analysis in advance, especially for long HDDs across environmentally sensitive features. While additional geotech information will never hurt, it’s impossible to sample the entirety of the profile. A site specific frac-out mitigation plan should be prepared and reviewed by all stakeholders on-site in case an inadvertent return occurs.
2. Anticipate more utility crossings than are shown on the construction drawings and documents.
Mapping of underground utility lines for water, sewer, electric or telecommunications can be unreliable. In most states, utility facilities can be obtained with a One Call to the relevant state authority. These utilities locate their facilities and a survey crew would then mark all utility lines along the proposed route.
However, in Michigan we encountered a different system as the state relies on utilities to maintain the data via atlases or utility record maps. This resulted in the receipt of atlases from utilities that varied in quality, preciseness, and completeness. Some utilities did not respond at all, while others provided outdated or otherwise unusable documentation. The process also missed any privately owned utilities such as irrigation water lines or septic systems. As a result, we found approximately 20% more utilities along our project route during construction than were shown on the atlases provided to us.
Fortunately, as is required, daylighting occurred prior to construction to locate all utility lines before trenching excavation work began. All presumed utilities were excavated to show the top of the line in order to pull depth and size information. Even with these precautions, delays did occur, and time was lost as utilities performed necessary repairs. The lesson learned is to expect the unexpected and be prepared with minimum separation requirements. Additionally, consider seeking approval for closer separation distances by installing a CP plate or other separation barriers between utilities in advance as you can’t assume utilities are always going to be located in the correct spot shown on the atlases provided during the design phase. Another option to help ensure a thorough pre-construction utility review is to perform a four-way sweep survey or SUE level A during the design phase. The four-way sweep is going to be a highly recommended survey method going forward on projects in congested areas of Michigan.
3. Be sure to plan and coordinate all aspects of hot line work far in advance, especially if a service outage is required.
At one end of the existing pipeline that we paralleled for most of the project, we planned to cut out a section and replace it with new pipe to reduce the number of crossovers of the two pipelines. As the existing line was the only source of natural gas to the Traverse City area, we knew we had to plan and sequence all activities carefully to avoid having the line out of service for an extended time. In fact, we were only granted a one-week outage, which included both the time to take the line out of service and reinstate service to the area.
In addition to the existing line replacement there were several station tasks that needed to be completed during the outage. Unfortunately in this situation, a clear punch list of items to be completed before and during the outage was not organized and tracked from the start of the project. This led to a late start on the completion of necessary tasks resulting in the need to reschedule the outage.
The lesson learned is that project engineers and contractors should be putting together outage tasks and schedules, as well as tracking what needs to occur week-by-week, beginning at the start of the project and leading up to an outage. This tracking is critical to successfully meeting schedules so outages can take place with time utilized as efficiently as possible.
4. Interdisciplinary coordination for facility work is crucial for efficient construction.
Although there was only one enclosed facility needed to house telecommunications equipment on this project, there were still structural and mechanical considerations throughout.
The pipeline had three facilities — one at each end and another in the middle. Each station had valves and other equipment that required grouting and shimming for leveling and raising from the foundation to specified heights. The drawings and specifications must clearly note such details as how much grout should be used to satisfy the required elevation between the foundation and the equipment, and whether pre-fab station buildings sitting directly on a foundation will have a concrete (foundation) or steel (part of the building) floor. It’s also important to consider what will be installed mechanically and structurally from all angles (or better yet, do some 3D modeling) to ensure that foundations are not in the way of any piping, valves, etc. that come off of the equipment. The mechanical and structural drawings must be coordinated to be sure elevations are correct throughout and that there are no conflicts.
In summary, it turns out to be true that no project construction will ever go exactly as planned no matter how many months of engineering and preparation before the construction notice to proceed. But with a willingness to be flexible, adaptable and listen to experienced team members, including your network of colleagues back home, a field engineering position will absolutely be a valuable learning experience with transferable knowledge that can be taken from one jobsite to the next and even back to the design desk.
This field engineer experience in Traverse City, Michigan was eye-opening and has provided me valuable insight into all the details and considerations that go into the construction of a pipeline project. While not all of these details and considerations can be resolved during the design phase, these are things that I will keep in mind through all stages of projects that I am involved in going forward. The experience has given me new perspective on natural gas pipeline projects and ultimately has made me a better pipeline engineer.
Check out more key takeaways from this pipeline field experience.