Technology Report 2022: Hammerhead Trenchless

SAME PATH Trenchless Technology

Synopsis

Gas utility owners have been proactively identifying and addressing pipelines in need of replacement, and some have realized the benefits of trenchless technologies within their pipeline rehabilitation and replacement programs. Reduced excavation is often more economical and less disruptive to utility customers, and utilizing the existing conduit greatly reduces the risks associated with relocating the line. Replacing pipe in the same location eliminates future locating mistakes due to abandoned facilities.

Following HammerHead Trenchless’ success using a “Same Path” pipe slitting/splitting technology (see Case Study 5 from the 2019 CGA Technology Report), a large North American gas utility approached them for a solution to replace numerous steel services, leading to the development of the SLX 1300 for copper and steel pipe extraction.
The extractor product was designed specifically for gas utilities to provide them with the cost-savings of ‘low-dig’ construction methods, the advantages of Same Path technology, and the efficiency to address multiple services in a given time frame.
The extractor unit requires a pit approximately 4’ by 4’ in size, located where the service connects to the main. The unit is lowered into the pit and connected to the hydraulic power pack at the surface from which it is operated. A cable is fed through the existing steel service from the machine to another access point. As the steel pipe and cable are extracted, the new pipe is being pulled into place in one seamless motion and extracted pipe can be cut using shears located on the extractor.

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Snapshot

Company Name(s): Hammerhead Trenchless
Company Website: https://www.hammerheadtrenchless.com/
Technology Category: Facility Installation
Stakeholder Target Audience: Designer, Facility Owner
Key terms /phrases: abandoned facility, existing conduit, extraction, same path, trenchless
Level of Production:
[technology is in full production and available for purchase]

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Abstract Introduction Pipe Extraction Technology Conclusions

Abstract

Innovation and advancements in trenchless technology have led to reducing damages to third party utilities. Locate requests continue to grow and some locate companies are managing live gas lines and abandoned/legacy pipe. Prior to Horizontal Directional Drilling (HDD) many gas utilities would open cut/excavate the gas main or services in order to install a new main or service in the same location. While HDD is a trenchless method that can install a gas main or service underground, the method does not account for the old main or service that was abandoned and no longer in use. With HDD being the primary trenchless installation method over the last 20 years, the US has seen a large increase in abandoned pipe. When a new line is installed under the old main or service, how does a contractor or locating company know which line is live or dead? With more utilities going underground and less easements to utilize, following the SAME PATH offers many advantages.

Steel natural gas lines were installed extensively in the 1960’s prior to the advent of plastic pipes and the establishment of federal regulations. Today, many bare steel lines continue to operate, although they may be nearing the end of their useful life as the lack of protective coating subjects the pipe to corrosion affecting its integrity. In 2018, the U.S. Department of Transportation reported over 1.5 million bare steel services still in operation.

Gas utility owners have been proactively identifying and addressing pipelines in need of replacement, and some have realized the benefits of trenchless technologies within their pipeline rehabilitation and replacement programs. Reduced excavation is often more economical and less disruptive to utility customers, and utilizing the existing conduit greatly reduces the risks associated with relocating the line. The amount of ticket locates are increasing at an exponential rate and decreasing the amount of old abandoned pipe will only help damage prevention in the future. Replacing pipe in the same location eliminates future locating mistakes on an old, abandoned service or main.

Following HammerHead Trenchless’ success using Same Path technology, a large North American gas utility approached them for a solution to replace the gas utility’s numerous steel services conjunction with other gas utilities facing similar challenges, HammerHead has released the SLX 1300 for copper and steel pipe extraction. This paper introduces the newly developed Steel Extractor system and the trenchless extraction process.

Introduction

Following significant natural gas pipeline incidents, the United States Department of Transportation (DOT) and the Pipeline and Hazardous Materials Safety Administration (PHMSA) issued a Call to Action in 2011 to accelerate the repair, rehabilitation, and replacement of the highest-risk pipeline infrastructure. Pipeline age and material are primary indicators of risk; pipelines constructed of cast and wrought iron, as well as bare steel, are among those that pose the highest risk. As of the end of 2018, PHMSA reported that approximately 97 percent of natural gas distribution pipelines in the U.S. are made of plastic or steel, and that the remaining 3 percent is mostly iron pipe.

Bare Steel – Bare steel (or uncoated) pipes, are also priority candidates for replacement. Bare steel was installed extensively in the U.S. until the 1960’s. It was not until the 1980’s that the use of coated steel and plastic pipe became widely accepted and preferred, where federal regulations mandated pipeline coatings. While many bare steel lines have been taken out of service, many still operate and pose a higher risk than modern materials. The lack of an outer coating subjects the steel to faster corrosion from its surrounding environment, so planning and careful inspection are necessary. Cathodic protection helps prevent corrosion, yet small, localized areas of corrosion are difficult to identify and can lead to pipeline integrity issues.

Existing Solutions for Bare Steel

Bare steel pipelines and services still operate across the United States as detailed in inventory reports published by PHMSA; in 2018, the total number of bare steel services in the U.S. was 1,861,137. With the prevalence of buried steel pipelines subject to deterioration from corrosion, there is a need for cost-effective solutions to maximize operators’ resources within their rehabilitation and replacement programs.

Figure 1— PHMSA PDM Report Service Count Trench indicates a decline in the number of bare steel services with the most recent figure reported being 1,861,137 bare steel services in 2018.

Trenchless technologies have increasingly gained acceptance by gas operators as manufacturers and contractors continuously develop and refine products and methods to address conditions unique to natural gas lines. Trenchless methods provide many benefits, including reduced impact on third party utilities, reduced social costs, and environmental benefits (e.g., protection of existing landscape and the ability to utilize the location of existing facilities). Alternatively, lines can be replaced with traditional open-cut method or, when the system allows, bare steel pipe may be inserted with new plastic pipe instead of being replaced outright.

HDD and horizontal boring with pneumatic earth piercing tools are widely accepted trenchless methods for installing new services. However, any new installation poses potential risks and additional expense. Such risks include the possibility of damage to third party utilities (Figure 2). Further, leaving an abandoned line in the ground could cause locating errors during any future construction, especially when the new line is installed in close proximity to the abandoned one.

Figure 2 — A cross bore is an example of damage to third party utilities with the risk of compromising the integrity of either or both underground structures.

While HDD and pneumatic piercing tools both offer some benefits of trenchless methods, HDD operations may not provide cost savings due to the large equipment requirements and need of highly qualified crews. Piercing tools are often more economical yet do not address the concerns of leaving the abandoned line in the ground.

Often the most expensive solution is traditional ‘dig-and-replace.’ Larger excavation and subsequent restoration requirements increase the cost of a replacement project. Additionally, excavation is not always feasible in congested site conditions, such as certain urban downtown areas.

A more economical solution is inserting the steel line with a new plastic pipe of a smaller diameter. The insertion method eliminates much of the excavation otherwise required but is not always viable as it requires the existing line to be oversized in order to undergo a reduction in Internal Diameter (ID) without negatively affecting its ability to deliver the necessary level of gas to the customer. Insertion also inherently creates an annular space around the new line which creates the possibility of trapping leaking gas within the annulus where it could build up and travel into the building. In addition, many times a copper or steel pipe may have a bend or small kink in the line preventing a smaller pipe to be inserted inside. For this reason, not all operators allow the insertion method to be used within their inventory.

While these existing technologies have proven effective, certain site conditions make their use costly, inefficient, or infeasible, presenting a need for innovative alternatives.

Design Criteria

Other trenchless processes exist that could be applied to bare steel but are not ideal for gas services. One such solution is trenchless pipe slitting (Figure 3), a process that has been developed to replace plastic pipes utilizing the same path as the existing line by using a constant-tension cable winch to draw specialized tooling through the pipe, splitting it in place, while simultaneously pulling in new pipe. This method has proven to be especially effective for the replacement of legacy materials, such as Aldyl-A, and has helped operators add efficiencies in their integrity management programs.

Figure 3 — Trenchless pipe slitting is a proven method for replacement of plastic pipes that utilizes the same location as the existing line.

Slitting is a proven technique for plastic pipe but was not ideal for bare steel services. Pipe splitting, a form of the trenchless pipe bursting method, requires a cable of sufficient width to be fed through the pipe in order to pull tooling back through the pipe to burst it. The amount of force required to burst steel mandates the cable be of a width often unable to pass through small-diameter steel services. So, while it may sometimes be possible to split or burst steel pipes, the equipment requirements generally make it less economical or even. In 2016 HammerHead Trenchless began developing concepts to specifically address small diameter steel service lines, keeping in mind the disadvantages of existing technologies as described.

Utilization of the existing location of the service was the primary objective of the product because it addresses some of the most significant concerns of existing technologies. It eliminates the need to rent new easement or pay rent on an abandoned line within the ground. Additionally, the use of a proven conduit eliminates risk to surrounding utilities and is safer for crews than other construction methods.

The solution to bare steel service replacement meeting all the named criteria is to extract it.

Pipe Extraction Technology

Pipe Extractor Product Development

Figure 4 — The pipe extractor requires a small excavation to access the pipe to be replaced. Minimum machine pit size is approximately 4 feet long by 4 feet wide.

Pipe Extraction Process

The extractor unit requires a pit approximately 4’ by 4’ in size, located where the service connects to the main. The unit is lowered into the pit and connected to the hydraulic power pack at the surface from which it is operated. A cable is fed through the existing steel service from the machine to another access point, typically at the riser. New PE pipe is attached to a pulling mechanism at the end of the cable opposite the machine (Figure 5).

Figure 5 — A small cable can be fed through the existing steel service to the access point opposite the machine pit. The cable aids in the extraction process as the unit’s cable grips pre-stress the cable which allows pressure to be applied to the entire length of the pipe.

A set of cable grips pre-stress the installed cable. The load is maintained while the machine’s jaws clamp the steel pipe and the cable within it. The machine then engages to pull the pipe out of the ground. The pre-stressing operation allows pressure to be applied to the entire length of the pipe, more load than the pipe alone may withstand. In circumstances where the welded joints of the pipe may have been compromised, the addition of the cable can also aid in keeping the pipe string together during the pull. The jaws release and the machine cycles forward to clamp and pull another segment. As the steel pipe and cable are extracted, the new pipe is being pulled into place in one seamless motion (Figure 6).

Figure 6 — PE product pipe is pulled into place simultaneously as the existing pipe is extracted.

Depending on ground conditions, the process can work without the use of a cable, in which case the product pipe is connected directly to the steel pipe opposite the extractor unit. In hard ground conditions, use of a pneumatic piercing tool with a specialized adapter can be used to apply force to the end of the steel pipe opposite the extractor machine to initiate movement. Running the piercing tool for a short amount of time is enough to ‘loosen’ the pipe from the surrounding soil, after which the pulling unit can extract the pipe unassisted.

Extracted Pipe

One significant design consideration for any technology with which pipe is fully removed from the ground is what to do with the extracted material. Behind the clamping jaws of the extractor unit are pipe shears. Once the pipe is pulled, the operator engages the shears snipping off a segment of the extracted pipe (Figure 7). The length of these segments can be cut in intervals of 10” as decided upon by the operator. Whether segments are cut every 10” or in longer pieces, the segment-cutting design makes it easier to manage the extracted material. Crews simply collect the sticks of steel from the extractor pit for disposal. By cutting the extracted pipe into short segments, pit sizes could be reduced and “no work zones” around the live gas main would also be observed. Since the operator has the option of when to shear the pipe segments, the speed of the extraction could be optimized to the pit size and main location.

Figure 7 — Side profile drawings illustrate the extraction process. Jaws clamp the pipe and the machine engages to pull it from the ground. Shears on the rear of the unit sever the pipe into segments.

Project Scheduling Considerations

The extractor product was designed specifically for gas utilities to provide them with the cost-savings of ‘low-dig’ construction methods, the advantages of Same Path Technology, and the efficiency to address multiple services in a given time frame. Same Path Technology utilizes the path of an existing service, which may sometimes reduce the requirements of multiple locates and “daylighting,” which can reduce the overall cost and duration of a traditional service line replacement. Some attributes of the final design were selected specifically so that a crew could work in sequence. One team could utilize an excavator to create the access locations for the first service and then move onto the next service since the extractor unit does not require an excavator arm to operate. A second team would perform extraction operations as the first team prepares the next location. A third team would then complete the connections after extraction is complete as the second team moves on to the next location.

Conclusions

The rehabilitation and replacement of dated natural gas pipeline materials is of high priority for North American gas operators, with cast iron and bare steel services being of highest importance. With the volume of services in need of replacement, a need exists for cost-effective and safe solutions. Trenchless technologies have gained acceptance in the gas industry as proven methods to reduce the costs and risks of open-cut replacement. However, there is opportunity to find additional innovative solutions for the unique challenges of construction of natural gas lines with safety being a critical factor. Based on initial feedback from operators using the technology, pipe extraction is a safe and economical solution for replacing bare steel natural gas services.

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