Tanya Vernon, Veolia Environmental Services, Special Services, Inc., Neenah, Wisconsin;

and Adam Erickson, Enbridge (US), Inc., Superior, Wisconsin

Veolia Environmental Services, Special Services, Inc (VES-SS) undertook a thoroughly integrated effort to design, build, and execute a pipeline repair project in conjunction with Enbridge Energy (US). The solution delivered to the client was both innovative in design and safe in project execution. For the purpose of this article, we provide some details about a) the design and fabrication of a novel Underwater Habitat Clamp and b) the safe execution of the project as a confined space permit-required project.

The background

After routine inspection discovers an anomaly in a section of Enbridge’s pipeline in North America, VES-SS dive teams were called in to install a PLIDCO Split+Sleeve. While the installation of the split sleeve allowed the pipe to remain in service initially, specifications did not allow mechanical clamps as a permanent repair without welding the two halves of the split sleeve together. For this, Enbridge requested a dry atmosphere, the removal of the sleeve and installation of a permanent tight fitting external reinforcing sleeve. This external reinforcing sleeve is designed in two parts, slightly larger in diameter than the main pipe. The two halves are placed around the pipe, compressed together using chain and jacking equipment, then welded along the longitudinal seams and fillet welded circumferentially around both ends. To accomplish a dry weld, an underwater habitat “clamp” was determined as the most appropriate solution.

The technology

The Underwater Habitat Clamp (UHC) is an interesting application of technology in three important aspects. First, while the engineering scope accounted for specific client and site parameters, it was additionally designed for multi-use, on multi-sized pipe, with capacity to “clamp” around the pipeline even where there is an uneven bottom. Secondly, unlike traditional “box or bell” solutions, the UHC, comprised of three sections, is easily positioned near obstacles such as other pipelines and dewatered completely. Further, its cylindrical shape, as depicted in Figure 1, plus strengtheners, allows the UHC to operate in one atmosphere of pressure or true hyperbaric mode. The resulting hybrid pressure vessel prototype meets strict confined space safety requirements, allowing Class A dry welding conforming to API Standard 1104, ASME Section IX, or other standards for numerous applications.

Traditional underwater pipeline repair may consist of either wet welding or the use of underwater “dry” habitats. Underwater wet welding has the potential to compromise pipeline integrity via both burn-through and hydrogen cracking. The use of habitats for underwater welding has been known offshore since the late 1960s. Inland, the use of underwater habitats is considered a viable option when cofferdams, diverting the river and wet welding techniques are excluded. Habitats are often custom built due to site specificities and thus are perceived as costly, both in terms of materials and time to deployment. Re-usable multi-purpose “bell or box” habitats have certain disadvantages: they traditionally have an open bottom which makes complete dewatering difficult or they possess size restrictions which prohibit use in many environments. In short, most habitats only possess one or two of the several features which have been engineered into the hybrid UHC.

Scope of work

The initial scope of work had several parameters. Of highest priority was a dry environment for a welded sleeve and the need to safely complete technical aspects of project execution. Expedient completion of the project was certainly important and later became more of a factor as winter approached and ice was more prevalent. The site provided additional challenges in the way of deployment of a habitat, notably the current of the river, which was at right angles to the pipeline. Deploying a barge equipped with a crane in the river was not considered feasible due to narrow conditions and depth constraints. Therefore, a land-based crane to lower the habitat was considered most desirable, and as such the UHC had certain weight restrictions. The seabed was also of considerable importance in the design. The seabed at the site was uneven hard pack sand. Two additional pipes, at the same depth as the effected pipe, were in close proximity and provided additional challenges. While not a specified requirement, the length of the UHC was originally designed to encompass an 8-ft long repair sleeve with the capacity to have a technician work either at end.

VES-SS’s senior divers/project managers assessed the scope of work and, rather than design a traditional single-use habitat, considered the multi-use habitat. Thus, additional parameters were added to the scope of work:

  • Adjustable aperture for variable pipe diameters
  • Depth from 15-33 feet (later modifications for true hyperbaric)
  • Mobility-had to be easily transported and deployed from land based crane
  • Weight (in compliance with capacity of the crane, buoyancy and stability)
  • Seabed-uneven, legs needed to be adjustable
  • Transportable by truck on U.S. highways under a wide-load permit.

Confined space safety requirements

Quite early in the design, the vessel was identified as a confined space. A confined space is defined as one with limited or restricted means of entry or exit, is large enough for an employee to enter and perform assigned work and is not designed for continuous occupancy by employees. Because the UHC was specified to accommodate two welders, a welder’s helper and an inspector, a number of confined space safety requirements were identified and designed into the UHC:

  • Two man-ways
  • Emergency man-rated lifting device (Figure 2)
  • Mechanical ventilation
  • Fresh air ducts
  • Fire extinguisher
  • Atmosphere monitoring equipment.

Project design

The UHC was initially conceived as a “clam-shell” in two halves opening along a single hinge, but was soon re-engineered as a three-part vessel which would open and close along two hinges rather than one, as suggested by a clam shell design. The change in design allowed for closer maneuverings over pipelines and lighter construction of the UHC for ease of transport and deployment from land. A number of additional design changes took place during fabrication. These are detailed below:

Spool pieces. Two spool pieces were added which effectively extended the man-ways to the surface. Each spool piece is equipped with welded rungs for ingress and egress. This was primarily driven by safety concerns. With extended man-ways, ingress and egress by non-divers was facilitated. The safe isolation of cabling (for lighting, etc), air handling pipe and stick welding gas tubes were also a concern which drove spool piece addition.

Clamps. Over 150 clamps were utilized in the structure to secure and compress the sealing surfaces, and each of these required manual tightening by divers. The number of clamps was arrived at via squash test of neoprene seals and the desire for minimal leakage. As an aside, cofferdams, the other proposed solution for the site, have no equivalent capacity for clamping or sealing due to their construction.

Hydraulic and electrical. The UHC has twelve hydraulic cylinders-two in each leg and two at each end of the 16-ft clamp for opening the bottom quarters or doors. VES-SS designed and installed the hydraulics; an internal lift system or “tram-way,” the legs themselves, and hydraulics for actuating lower doors. Each of the legs was controlled separately in order to compensate for un-even seabeds.

Stiffeners, grates and plates. Stiffeners were integral to the light construction of the pressure vessel which allowed for ease of transport as well as deployment from the bank. The stiffeners further allowed for additional weight to be placed above the waterline for deployment of personnel and tools, so a metal grate/deck was constructed for topside, and an additional metal grate was designed to be situated in the UHC for welder and technician comfort. The light frame design required that additional weight be added to the UHC, on-site, after dewatering. Hence a number of steel plates were designed to be added to special compartments on the UHC. These plates, along with four 1,000-lb anchor feet, added approximately 14,000 lbs of weight to secure the structure in a current.

There was a significant amount of seal welding involved in the fabrication process and in the end, there were at least 1,000 hours of fabrication time in the above processes. Ultimately, post weld heat treatment was used for stress relief.

Safety integrated engineering

Senior experienced divers were involved with the UHC from its inception through to design, fabrication and finally, project execution. Senior divers prepared sketches of the UHC which were passed to mechanical contractors for drafting, refinement, layout, design and specification. Divers continued to provide input throughout the refinement and fabrication stage. The dive superintendent, who was ultimately responsible for the safe execution of the project on site, was also responsible for all of the flat sealing surfaces which involved durometer testing of various types of neoprene. The same diver designed an overhead trolley lift system within the UHC in order to allow tools to be kept clean and dry and for portable lifting equipment to help maneuver the heavy split sleeves used for the repair. The lift system also gives the divers more freedom and work space to move about safely within the UHC. Extensive dive safety experience ensured design elements, such as the man-ways and emergency man-rated lift system, adhered to strict codes for inland and offshore application.

Project implementation

Upon completion of fabrication, trials of the UHC were made with a sample 40-ft piece of pipe. VES-SS tested the sealing surfaces, clamps, hydraulics, lift systems, emergency rescues and deployment plan. The UHC components: legs, hydraulics, weights, metal grating and assorted dive vans were then trucked over-road to the site using standard haulage methods. On-site work commenced November 15, 2005, and the project concluded on December 12, 2005. The project followed the execution plan described below.

Site preparation

The steep embankment to the UHC deployment zone had to be extensively graded prior to project commencement. After grading, the bank of the river was prepared with large timber mats to a depth of two feet with a total area of approximately 80 ft x 150 ft. This allowed cranes, site vehicles and tools to be near the deployment area. The distance from the crane’s center of balance to the drop site was approximately 87 ft. The area surrounding the effected pipe, approximately 30 ft x 40 ft and to the depth of 10 ft, was excavated by VES-SS utilizing diver-assisted dredging techniques. This was accomplished by a 10-in. vortex pump in two weeks. After bottom sand was pumped upstream, the following steps were followed:

  • Removal of intruding anchor block on target pipeline
  • Removal of intruding anchor block weight on adjacent pipeline
  • Placement of sandbags to support UHC feet and anchor pads.

Each of the launch-pad feet are constructed of 36-in. x 36-in. plates. Depending on the seabed, additional sandbagging or Submar mats may be required. In this instance, four pallets of 50-lb sandbag were utilized. Pipe work included:

  • Removal of the split sleeve clamp
  • Removal of pipeline mastic coating
  • Re-inspection of anomalies.

Mobilization of the UHC

The UHC project execution plan and emergency confined space rescue were trialed prior to site deployment. The two sections of the 8-ft repair sleeve were also preloaded into the UHC prior to deployment in the water. The next steps included:

  • Deployment of UHC into water using land-based crane
  • Weighting to compensate for buoyancy when UHC is dewatered
  • Anchoring
  • Application of sealing surfaces
  • Seal annulus between pipeline and UHC via installation of Link-Seal
  • Adjustment of small clamps
  • Dewatering using pumps
  • Installation of deck grating
  • Installation of emergency man-rated lifting devices
  • Installation of internal devices-smoke extractors, lighting, fresh air ducts, detection and monitoring devices.

Repair work

Repair work under confined space and/or Hot Work permits included:

  • Grit blasting of pipeline to prep surface for more detailed inspection and welding
  • Sleeve installed and welded by Enbridge personnel
  • Magnetic particle testing of welds by NDT contractor
  • Replacement of coating using two-part epoxy.

UHC demobilization

Demobilization of the UHC entailed the following activities:

  • Removal of topside cabling, air handling pipe, spool pieces and lift equipment
  • Removal of lighting, air control and hydraulic system controls
  • Man-ways sealed, ball valves released and vessel flooded
  • Weights brought to the surface
  • Legs retracted
  • Unsealing of UHC
  • UHC brought to the surface by crane.

Clean-up activities included:

  • Replacement of coating at UHC sealing points
  • Refilling of area by clam-bucket crane with original material from upstream
  • Additional filling of area, to a depth of 8 inches by rip-rap (rock armor) for additional protection of pipe
  • Removal of heavy equipment
  • Removal of matting
  • Re-grading of area
  • Survey of area to ensure sufficient water depth to accommodate boat traffic.

Site preparation took approximately three weeks of the noted timeframe (November 15th to December 12th). Actual welding repair work was completed in one 12-hour day, followed by testing, demobilization of the UHC and site clean-up as detailed above.

Safety and job execution

The UHC was deployed in November-December 2005 per the scope of work; however, the river iced over early in the execution. The thin ice was later replaced by massive floating ice chunks (Figure 2 depicts the winter conditions and safety considerations). For this reason, near the end of the project, one diver alone was assigned regular ice breaking duties to ensure that no large chucks would hit the sides of the spool pipes or other parts of the UHC. It was crucial that the river area should not be allowed to freeze over entirely, thus making the removal of the UHC difficult, if not impossible.

Temperatures fell to well below freezing, and another major concern began to be the durability of the sealed surfaces. They had been tested for durability under pressure, but not under pressure with sub-zero conditions, so divers regularly checked the sealing surfaces for signs of leakage. A minor leakage factor of about a gallon per hour was experienced, but this was quickly dewatered. Personal Protective Equipment (PPE) was a key safety aspect, with the following always a consideration: need for emergency rescue from the UHC, water safety, and diver hypothermia. Job safety analyses/tool box talks from the project files indicate the following notable inclusions (see also Table 1):

  • Written project execution and emergency rescue plan for the installation and use of the UHC.
  • Case study of confined space entry, FACE85-05 “Confined space incident kills two workers, company employee and rescuing worker.”
  • Confined space rescue procedure and checklist (see Table 2-VES-SS Confined Space Checklist).

The UHC was considered a confined space only up to the day of welding. On the single day of welding, the UHC was considered a confined space with the inclusion of Hot Work (Figure 3). This was one of the riskiest days for the project.

As suggested, the project involved risk, not only because of the confined-space and Hot Work but also due to the freezing weather conditions and snow. The confined space work fell under the VES Industrial Services work permit and the Hot Work fell under Enbridge Energy (US). It should be noted that all of the cables for the ventilation, welding equipment, lighting, etc., went through one man-way, while the other man-way was reserved for ingress/egress. On the day the welding took place on the pipeline (keeping in mind that line was not shut down), the two welders were monitored by an attendant, and all of the team were trained for confined-space rescue. Welding gas cylinders are never to be brought into confined spaces, and these were actually stationed at the riverbank.

Analysis and summary

The results are in reference to the safe operation of the UHC and project execution. The UHC met the expectations of both parties in all respects. The seals withstood not only the external water pressure, but also the ice conditions. In retrospect, th5e vessel itself might comply with “pressure vessel human occupancy” or PVHO requirements. The addition of design elements detailed above allowed for safe and efficient UHC utilization. The execution of the job itself experienced no downtime due to weather, which in no small part was due to excellent project management and relationship with the client.

The UHC can be deployed in a number of environments: offshore shallow water, contaminated water, swampy or brackish water, hazardous water, even waters where divers or other methods would pose an ecological threat, and any water depth to 33 ft. The hydraulic legs with launch pad feet allow for deployment on: soft or hard sand bottoms, silt, rip-rap, gravel, mud and clay. With minor modifications in design, the UHC can be deployed in true hyperbaric mode.

Conclusion

The design, fabrication and implementation of a hybrid UHC, known from both the offshore and inland pipeline repair industries, allows for safe pipeline maintenance, where integrity and flow are not compromised at any stage during project execution. The easily transported and deployed UHC allows for numerous applications such non-destructive testing undertaken by UT, mag-particle, caliper, and x-ray technologies, while VES-SS dive teams provide expert and safe project management and execution.

Acknowledgments

The authors wish to acknowledge Enbridge Energy (US) for cooperation, participation and interest in continued collaboration and application of the UHC technology. The authors also wish to acknowledge the contribution of Lance Birdsall, currently the EHS Regional Coordinator for VES-SS and also the VES-SS superintendent on the project. Based on a paper presented at ASME’s 7th International Pipeline Conference, held September 29-October 3, 2008, in Calgary, Alberta, Canada.