Gerald F. Mouser
Questar Pipeline Co.
Rock Springs, Wyo.,
Questar Pipeline Co., Salt Lake City, completed an 81-mile, 20-in. pipeline interconnect last summer between its southern and northern transmission systems in northeastern Utah. It was placed in service in September 1990.
In addition to connecting extensive and formerly separate segments of the system, the connection has significance for larger gas-movement patterns west of the U.S. Rocky Mountains, as has been earlier described (OGJ, Oct. 1, p. 79).
Completion of the North-South Pipeline project marked the conclusion of more than 3 years of planning, permitting, and construction activities for the company. Prior to construction of the pipeline, a number of environmental studies were performed and appropriate regulatory approval was obtained.
Construction was accomplished during 1990, primarily adjacent to an existing pipeline corridor, but through extremely difficult and sensitive terrain.
REQUIREMENTS, PERMITTING
The Questar Pipeline system has evolved over the years to consist of a northern system, which generally runs from northwest Colorado through southwest Wyoming into northern Utah, and a southern system which runs from western Colorado through northeastern Utah (Fig. 1).
In recent years, gas-balancing problems between the systems, the need to maintain control over production and transmission inputs, and the need to provide dependable service to sales and transmission customers demonstrated the need for an inter-tie between the two systems.
The new pipeline crosses the eastern edge of the Uintah Mountain range. From its southern terminus at Fidlar station, the pipeline runs northerly past the Red Wash field, then past Jensen, Utah, over Diamond Mountain and into Browns Park before making a junction at the company's pipeline facilities near Clay basin, just south of the Wyoming state line (Fig. 1).
Preliminary route selection revealed that a major portion of the pipeline alignment would cross lands managed by U.S. Bureau of Land Management (BLM) and State of Utah agencies. In addition, a large percentage of the route would run parallel to a pipeline corridor which contained up to four existing pipelines: Mid-America Pipeline Co.'s (Mapco) NGL pipeline, Chevron Pipe Line Co.'s slurry phosphate pipeline, Chevron Pipe Line CO-'S CO2 pipeline, and Northwest Pipeline Corp.'s natural-gas pipeline.
Appropriate representatives of the managing agencies were involved in the initial route reconnaissance during fall 1987, and where necessary various alternative routings were identified for further evaluation.
Formal applications were made to the BLM for right-of-way consideration in December 1987 and to the U.S. Federal Energy Regulatory Commission (FERC) for regulatory approval in February 1988.
The BLM district office in Vernal, Utah, coordinated environmental scoping meetings which were conducted during May 1988, and an outside consultant was selected to draft an environmental assessment. To satisfy provisions of the National Environmental Protection Act of 1964 (NEPA), on site studies were conducted by agency wildlife specialists or outside consultants for threatened and endangered species and for cultural, historic, and paleontological resources.
These studies identified areas and seasons to be avoided during construction due to wildlife activity, pinpointed locations containing significant cultural (Fremont Indian) and paleontological (dinosaur fossil) resources, and designated areas which required additional site study prior to construction. In addition, comparative analysis was made of the effect of the various proposed routes on watershed, visual resources, vegetation, land use, and recreation.
Results of these studies were incorporated into the environmental assessment and helped determine final pipeline alignment. Based upon preliminary environmental analysis, Questar Pipeline elected in January 1989 to amend its applications to avoid a proposed routing through areas considered sensitive to the BLM and the Utah Division of Wildlife Resources.
In addition, several minor realignments were accomplished along the pipeline corridor to reduce disturbance of cultural sites. Also, one route change was made to avoid a rock formation found to contain dinosaur bone fragments.
The pipeline route crossed an isolated area containing a sizable density of prairie dog burrows and required a study for the endangered black footed ferret. The detailed study was conducted by an outside consultant but failed to find the endangered mammal along the right-of-way.
Upon completion of all analyses, the environmental assessment was completed during summer 1989. The approved pipeline alignment was 86% on BLM or State of Utah lands and 14% on private or Uintah or Ouray Indian lands.
Based upon the findings of the environmental assessment, Questar Pipeline developed a detailed construction-operating plan in September 1989 to address specific stipulations pertaining to the pipeline installation and route rehabilitation.
Included within the plan were descriptions of right-of-way widths, location of staging areas, "borrow" areas (for supply of fill and padding material), and access roads, seasonal avoidance of restricted wildlife, and special construction techniques for sensitive areas.
Final BLM right-of-way grant and FERC approval were obtained in late 1989. Remaining permits and easements were secured in early 1990.
DESIGN, MATERIALS
The 20-in. pipeline and all fabricated assemblies were designed to meet a maximum allowable operating pressure (MAOP) of 960 psig. Inter-tie with existing facilities will limit MAOP to 936 psig.
Previous route survey had shown the entire alignment to lie within a U.S. Department of Transportation (DOT) Class 1 location. As a result, the line pipe selected was 20-in. OD and 0.250-in. W.T., with a specified minimum yield strength (SMYS) of 56,000 psi.
Pipe of heavier wall thickness (0.281 in., 0.312 in., and 0.375 in.) was specified for particular road and river crossings. Casing pipe (24 in.) was used at major road crossings when necessary to accomplish pipe installation or when specified by the governing agency.
Locations for sectionalizing block valves were selected to satisfy Department of Transportation Part 192 spacing regulations. Assemblies were designed with buried full opening 20-in. valves with 8-in. blowoff piping.
Projected operational needs required the 20-in. inter-tie be designed for bi-directional flow conditions. End assemblies were planned to allow either northerly or southerly gas flow and also permit various operating configurations within the station piping.
Pigging facilities, designed for each end of the pipeline, were configured to allow either launching or receiving of 20-in. pigs. Also, the barrel and by-pass piping at each launcher-receiver was equipped with flanged connections to permit elongation of the barrel to accommodate internal inspection equipment.
Also, 3R welded pipefittings were specified for use throughout the pipeline and at launcher-receiver assemblies. In addition to pigging facilities, piping additions on the southern end included tie-in to existing station facilities at Fidlar compressor station, located at a junction of several gathering and transmission pipelines within the Uihtah basin production area.
Piping, metering, and control assemblies were designed to allow the new 20-in. pipeline to operate on either the suction or discharge of existing compressors, or completely bypass the station piping. Automation was provided to allow major operating modes to be controlled remotely by the company's gas control department in Salt Lake City.
Facilities on the north end included the pigging facility, a 130-bbl capacity liquid receiver, and tie-in to existing pipeline and measurement assemblies adjacent to Kastler compressor station.
Design was accomplished to allow two main modes of operation:
- Flow northward to or from the company's transportation exchange facilities near Rock Springs, Wyo.
- Flow to or from Kastler compressor station for injection or withdrawal into underground storage at Clay basin.
Line pipe for the project was manufactured by American Steel Pipe at its Birmingham, Ala., ERW mill to API 5L specifications. All pipe was supplied to maximum lengths of 65 ft to reduce transportation and construction costs.
Pipe was shipped by rail car to the Energy Coatings Co., Ft. Collins, Colo., facility where it was coated to Questar Pipeline's specifications with Napgard 2501 fusion-bonded epoxy (FBE) coating.
After coating, pipe was stored on site for transportation by truck to the construction project. Raychem heat-shrink sleeves were purchased for coating of field joints. Valves, fittings, pipe, and actuators required for end facilities were acquired in early 1990 to allow company crews to fabricate and test the majority of these assemblies before field installation.
PIPELINE CONSTRUCTION
Field construction of the 20-in. pipeline was performed in two phases.
In order to avoid damage to irrigated croplands near Jensen, Utah, approximately 21/2 miles of 20-in. pipe were installed during February 1990. The work was accomplished by Sterling Construction Co. Sterling, Colo.
Construction of the remaining 79 miles, including river crossings and hydrostatic testing, was done during the summer of 1990 by Gregory & Cook Inc., Houston. This company had previously installed CO2 and phosphate pipelines through portions of the same right-of-way corridor during 1985.
Work commenced in late May on the south end of the project. Throughout the construction, contractor operations were confined to right-of-way widths, access roads, and staging areas previously authorized by the BLM and other government agencies and landowners.
Working northward, the contractor used one sizable construction spread for the pipeline installation. In addition, a small equipment spread was used to prepare the right-of-way in an extremely rocky area above Browns Park on the north end of the project (Fig. 2).
Although daily performance depended upon site conditions, exceptional progress was made on all construction activities. Right-of-way crews averaged 11,000 ft/day but made as much as 7 miles in 1 day under optimum conditions.
Ditching operations averaged 10,000 ft/day and achieved a maximum of 41/2 miles/day. Line pipe was hauled to the job site by Black Hills Trucking, with contractor trucks used to string pipe along the right-ofway. Bending crews averaged 11,600 ft/day.
Pipe welding was accomplished by a firing line and averaged 180 pipe joints (approximately 11,000 ft)/day. All field welds were inspected by radiographic techniques by Southwest X-Ray under contract to Questar Pipeline.
As noted previously, the new 20-in. pipeline was installed adjacent to a right-ofway corridor containing at times as many as four active pipelines. This required field precautions to avoid damage to the existing facilities.
Representatives of other pipeline operators were on site during line crossings and other critical parallel construction activities. Excellent cooperation among all parties prevented damage or interference to existing facilities or operations.
Coating, lowering, and backfill crews accomplished pipe installation after welding. Construction specifications required use of padding machines for backfill operation to reduce the use of rock shield. Cleanup crews then restored the right-of-way to original contours.
Final seeding was accomplished before winter snowfall.
During peak construction activity, the contractor had approximately 300 personnel on the project. All inspection was performed by Questar Pipeline employees.
RIVER CROSSINGS
At two locations the pipeline alignment crosses the Green River, a major tributary of the Colorado River. As a result of differing site conditions and particular seasonal restrictions, two different construction techniques were used for the two pipeline crossings.
The crossing of the Green River at Browns Park was constructed by conventional trenching methods. All work within the river channel was accomplished with equipment and techniques to reduce sedimentation.
During low-flow conditions in late July, the contractor excavated a 10-ft deep trench across the 300-ft wide crossing.
The 20-in. pipe section, containing bolt-on concrete river weights, was then carried into the river and installed in the trench. A minimum of 7 ft of cover was obtained over the pipe crossing.
Installation of the 20-in. pipeline at the Green River at Jensen was accomplished by horizontal directional drilling techniques (Fig. 3). This method was employed to ensure proper installation of the 20-in. pipe below the silty river channel and to avoid disturbing fisheries along the river.
Directional drilling was performed by Harcro Inc., Tulsa, as subcontractor to Gregory & Cook.
First a 2 7/8-in. pilot hole was drilled under the 1,000 ft crossing, followed by a 5-in. washover pipe.
Upon completion of the initial bore hole, a 30-in. diameter hole was cut by a reaming tool.
Finally, the prewelded 20-in. pipe section, more than 1,000 ft in length, was pulled underneath the river bed from bank to bank.
TESTING, OPERATION
After installation, the entire pipeline was hydrostatically tested.
Because of significant changes in elevation over the 81-mile pipe route, 19 test sections were required. Test pressures within the sections ranged between a minimum of 10% above MAOP and a maximum of 100% SMYS of the pipe. All hydrostatic testing was for 24-hr duration.
In addition, the river crossing at Jensen was strength tested before and after pulling of the 20-in. pipe under the river. Water was drawn from the Green River at both Jensen and Browns Park and filtered before being pumped into the pipe sections.
After testing, water was discharged in accordance with State of Utah regulations at approved locations. In order to assure that the final discharge met agency guidelines, Questar Pipeline provided an additional filter unit capable of screening suspended solids down to 50 m.
Discharge water was sampled throughout the testing operation to ensure that water quality met State of Utah regulations. After dewatering, the 20-in. pipe was dried and cleaned by running a series of swab pigs through the sections.
Final drying was performed by Coltier Services, subcontractor to Gregory & Cook, using vacuum drying techniques.
Upon completion of drying and final tie-ins, the 20-in. pipeline was purged and gas packed for service.
On Aug. 30, 1990, gas production from the Uintah and Piceance basins began moving south to north toward the company's Clay basin storage field. Since initial operation, volumes have varied based upon producer and market commitments, but flowrates have approached the certificated pipeline capacity of 86 MMcfd.
As a result of this project, Questar Pipeline is now better able to balance gas flowrates between its pipeline systems, to fulfill commitments to existing transportation customers more effectively, and to meet the demands of its primary resale customer, Mountain Fuel Supply Co.
The new pipeline interconnect also allows the company considerably more flexibility in offering future gas transportation and gas-storage services to producers and marketing firms.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.