The following paper highlights 2 different pipeline reroute projects. There are many similarities, but the main difference is in the approach of each project, i.e., a traditional multi contractor involvement vs. a more turnkey approach. The common thread is the technical complexity and multi-facetted nature of these two projects.
Our first case study centers on a pipeline reroute through a river.
The 18” gas transmission pipeline was constructed in 1980’s and the section under discussion crossed a river of approximately 330 feet wide.
Over the years the riverbanks eroded and exposed the gas pipeline to such an extent that people started using the exposed pipeline to cross the river.
The project focused on installing a replacement section of 18” pipeline at least 20’ underneath the riverbed and performing a live tie-in by hot tapping and plugging.
The second case study centers around the relocation of a transmission gas pipeline (12”) in preparation for the construction of a new rapid rail transit system.
The project required a replacement section of 12” pipeline to be installed underneath a very busy motorway employing HDD (Horizontal Directional Drilling) and ultimately performing a tie-in using hot tapping and plugging.
Pipeline relocation project scope of work
In broad terms, a typical relocation project scope could look like this:
- Locate and identify adjacent and intersecting services and other assets.
- Prepare Right-of-Way (RoW).
- Staging area
- Receiving pit.
- Expose tie-in positions.
Pipe welding & coating repairs
- Weld pipe string & NDE.
- Hydrotest and dewater.
- Drying and packing with Nitrogen in certain cases.
- Coating repairs at welded joints.
- Prepare pipe for pullback.
Horizontal Directional Drilling
- Select and stage plant & equipment.
- Set out tracking and navigation system.
- HDD activities.
- Pullback and install pipe string.
- Hot tap and linestop.
- Cutting & welding.
Characteristics of a typical relocation project
Multi-disciplinary or multi-faceted.
It is not unusual to deploy the same resource types as you would on a large pipeline project.
- Normal pipeline construction is not a simple endeavor and now you are adding a few more complexities to the equation.
Short execution durations.
- Once all the permitting, engineering and designs are complete, the execution phase is relatively short, when compared to a typical pipeline construction project.
Working on or near live pipelines
- Not only in proximity of live pipelines but tying into an operational, live pipeline
- Usually in proximity of an array of service/utilities.
This paper focuses on two approaches to execute relocation projects and those are represented schematically below in figures 1 and 2.
I am referring to the above approach as outlined in figure 2 as turnkey, but in the true sense of the word, it is probably more accurate to term it along the lines of a “Comprehensive approach”.
Case study 1 – River crossing and live tie-in.
- Gas transmission line (18”) – constructed in the 1980’s
- River flow characteristics changed over the years, exposing the originally constructed crossing.
- Replacing existing crossing section at a deeper invert level below the riverbed.
- Replacement crossing tie in.
Brief project synopsis
- Prepare right of way (RoW)
- Provide line pipe 18” API 5L X65 0.562” WT – 1,155 feet
- Offload pipe lengths along the RoW
- Weld pipe string – 1,155 foot including all NDE
- Hydrostatic testing of completed pipe string and dewatering & drying on completion.
- Repair coating at welded joints (Mainline was coated in 3LPE coating)
- Install pipe rollers and stage completed pipe string for installation.
- Prepare staging area for Horizontal and Directional Drill (HDD) rig, mixing system, drill pipe and ancillary equipment.
- Prepare and install magnetic guidance system.
- Install and weld 18” linestop fittings for two double position linestop operations to facilitate an on-stream linestop.
- Complete HDD drilling, back reaming and pullback to install completed pipe string.
- Hot tap and linestop activity and tie in newly installed pipe string. The intention with this paper is not to be too granular with each activity or aspect of the construction, but rather to illustrate the difference in outcomes by executing similar projects from either a traditional or a turnkey approach.
The customer appointed a renowned engineering company to act as their representative (PMC) and the work was let as follows:
- Minor earthworks
- Prepare RoW
- Prepare HDD staging area
- Locate, identify, and expose existing pipeline and tie-in positions.
- Trenching where required
- Pipe transportation & offloading on RoW
- Coating repair
- In-service welding
The customer then performed their own hot tapping and plugging to tie in the newly installed crossing section.
Even though the project was completed successfully, it was 1 month late, and exceeded the budget.
The biggest reason for the delay was scheduling and interfacing between all the contractors, despite the best efforts by the customer’s consulting engineering company.
Here are some of the challenges and causes for delays and frustration:
- All the different role players established as planned; so, from this standpoint the playing fields were level.
- As the site was located near the coast, the site did experience an unusual level of rainfall, which was not anticipated in the project schedule.
- The earthworks contractor was tasked to prepare the RoW and place the pipe roller cradles at predetermined positions approximately 15’ apart.
- During the pullback, some pipe cradles collapsed due to sagging soil and (1 set was placed on sandbags and this was only noticed after the fact). The collapse of the pipe cradles caused the pipe on those cradles to flex slightly and contact the steel frames causing extensive damage to the 3 LPE coating on at least 10 sections of pipe. Once we assessed the extent of the damage, we realized that the 3 LPE coating could not be sufficiently repaired for us to confidently install a gas transmission pipeline underneath a riverbed, and the decision was made to cut and replace all the affected sections.
- The pipe was already 30% into the drilled tunnel and we had to remove the pipe section before the repair process could proceed.
- There was not a clearly defined scope that tasked the earthworks contractor with placing the roller pipe cradles along the RoW, but rather a loose arrangement between the parties on site to assist one another.
- The welding contractor had not expected to cut and prepare the pipe sections and frankly, the most expedient method of cold cutting and bevel preparation was unknown to this contractor.
- Replacement pipe sections were in the customer’s stockpile yard and arrangements had to be made to uplift and transport these to site and remove the damaged sections. This had to be arranged separately as none of the contractors on site had this capacity.
- It is important to note that we were working against the clock for various reasons, the one important being the fact that our HDD crossing was in a final reamed stage, and we could not have the tunnel collapse.
- It is fair to say that not every party on site had the same sense of urgency because the repairs were not contained in the construction contract and these activities were on a dayworks (time and material) basis. So, no common goal to speak of, at least the short- term goal to complete the repairs as soon as possible.
- Approximately 4 weeks of intense effort later, and the pipe string was pulled back smoothly through the HDD bore and the tie-in commenced shortly thereafter.
Construction projects hardly ever go as planned, but if there are many different parties to a specific project, they do not necessarily share the same vision and goal, especially when the project tends to make the daily schedules obsolete.
Let’s see how it worked out on a project where the approach was more along the lines of a turnkey.
Case Study 2 – Pipe relocation project in preparation for a new rapid rail transit system.
- Gas transmission and distribution pipeline system (6” – 12”)
- The planning and construction of a new rapid rail transit system required various diameters gas transmission and distribution pipelines to be relocated.
- In certain instances, the relocation was relatively small, in the case where structural concrete foundations were to take place and the pipe section rerouted and, in some cases, where an entire pipeline section had to be rerouted to make way for a below- grade rail section.
- The full benefit of a turnkey approach on a relocation project is better illustrated on the 12” line section where we had to cross a very busy motorway (using HDD) to relocate the new pipe section.
Brief project synopsis
- Prepare right of way (RoW) where applicable
- Provide line pipe ranging in diameters from 6” to 12” API 5L X52
- Transport & offload pipe lengths as required
- Welding of pipe strings and all NDE as required at each site.
- In-service welding of hot tap and linestop fittings as required at each site.
- Hydrostatic testing of completed pipe strings and dewatering & drying on completion. Application of an LDPE anti-corrosion tape wrap system for all diameters as required. Prepare staging area for Horizontal and Directional Drill (HDD) rig, mixing system, drill pipe and ancillary equipment. This was the case only for a 12” high pressure transmission section.
- Complete all earthworks.
- Install and weld 12” linestop fittings for two double position linestop operations to facilitate an on-stream linestop.
- Complete HDD drilling, back reaming and pullback to install completed pipe string. Hot tap and linestop activity and tie in newly installed pipe string.
As in the previous case study, the customer used the services of a PMC to oversee the project in all its facets.
In this case a single contractor was selected for the entire project, including the 12” relocation using HDD.
The following activities were required:
- Minor earthworks
- Pipe transportation & offloading on RoW
- Coating application
- In-service welding
- Hot tap and linestop
- Pipe abandonment (old 12” section)
- Site cleanup and rehabilitation
We experienced challenges with the HDD pilot bore due to the depth under the motorway coupled with the fact that the motorway surface was constructed from reinforced concrete and the reinforcing steel caused havoc with our navigation and steering, but we prevailed and completed the pilot bore in less than 24-hours.
During the first stage hole opening, the drill pipe broke at the reamer connection and only after a few trials did we figure out that the initial portion of the hole was in rock and for approximately 18’ – 20’ there was some sort of void which caused the hole opener to sink below the initial invert level, and so doing, exceeded the maximum bend radius of the drill pipe causing the connection to break. We lost one hole opener before we solved the challenge and completed the HDD activities.
The other unforeseen and unplanned activity was the eventual tie in position. The road reserve had to be maintained and the customer servitude was extremely narrow due to a developed industrial property bordering the servitude. This meant we had to maintain the level underneath the motorway all along until we reached the servitude, where we had to affect the tie in. The advantage of using HDD was that our setback distance was far enough away to avoid exceeding the drill pipe bend radius while maintaining the required depth at the tie in position.
What this meant was that our tie in would have to be done at a depth of almost 30’ and we were limited to shoring as our single choice to maintain trench integrity and safely execute the tie in at this depth.
Within 2 weeks we had designed, procured the material, and built a bespoke shoring “box” that we would lower into the excavation, and create safe access and working conditions for everyone required to complete the tie in, perform NDE, repair the coating and place the first stage of backfill.
Having one contractor own the above challenges made for a far more expeditious conclusion with minimal impact to the project schedule.
The entire project was successfully completed within the required timeframe and budget.
For another great example of a very successful specialist turnkey project, please follow this link:
These two relocation projects were selected to illustrate the advantages of a turnkey approach, which is summarized below.
- A turnkey approach to the execution of smaller, technically niche pipeline projects does not require the same number of customer/contractor interfaces.
- The reduction in customer/contractor interfaces results in improved efficiency, lower project cost, shorter project delivery cycle.
- Unless each party to a construction project is and remains aligned for the project lifecycle, the outcome will remain be unpredictable at best, but realistically, negative.
- Bigger is better, but not all the time. Having a big general contractor execute a small, bespoke and specialist project without the required experience in the niche environment, is not by default the smartest or even the correct choice.