NORTHWEST PIPELINE EXPANDS ITS SYSTEM

Barrie B. McCullough, John T. McAughan, Ray C. Gromer
Northwest Pipeline Corp.
Salt Lake City

Northwest Pipeline Corp., Salt Lake City, has placed in service its $432 million gas-transmission system expansion. The 433-MMcfd project increased Northwest's total deliverability to 2.4 bcfd.

Northwest Pipeline's experience shows that, in today's regulatory environment, completion of a major gas-transmission expansion takes at least 3 years from inception to final cleanup and requires a complex implementation plan that involves customers, all levels of government and its agencies, and landowners.

The expansion was primarily needed for Northwest customers who were experiencing increased demand for natural gas in the U.S. Pacific Northwest and intermountain regions.

The increased demand was the result of growth in residential, commercial, and small industrial loads; in residential and commercial conversions to natural gas; and in shippers who converted interruptible transportation use to firm.

Table 1 presents shippers by type and what each type would require on the expanded system.

DYNAMIC, BIDIRECTIONAL FLOW

Northwest Pipeline filed for authorization from the U.S. Federal Energy Regulatory Commission (FERC) to expand its natural-gas transmission system on Dec. 31, 1990, and started receiving authorizations to begin construction segment by segment on July 27, 1992. Commissioning occurred earlier this year with official start-up on Apr. 1.

The expanded facilities included 362 miles of pipeline loop, 113,572 hp of compression, modifications to five existing compressor stations, modifications to 46 meter stations, and the addition or modification of 32 communication sites.

The added facilities increased Northwest's total facilities as shown in Table 2.

Northwest Pipeline's gas-transmission system has numerous receipt (58) and delivery (431) points along its system. Additionally, there can be multiple null flow points at one time because of bidirectional flow requirements.

The system starts at the Canadian border near Somas, Wash., and traverses seven western states to the Blanco hub in New Mexico.

Because of its numerous receipt and delivery points and the need to meet new transportation requirements along the system, the new facilities were also spread throughout it.

The new system design also optimized between compression and pipeline costs, considering both capital and operating and maintenance (O&M) costs.

The Stoner transient flow model was used for designing the facilities required for critical seasonal and daily swings on the Grants Pass laterals in western Oregon (Fig. 1).

COMPRESSION FACILITIES

The compressor-station facilities were designed with Northwest Pipeline's standard modular design philosophy and incorporated the latest technological developments using programmable-logic controller (PLC) control.

This design approach allows a large portion of the station equipment to be prefabricated off site such as the unit valve and fuel-gas skid. The stations were all fully automated for unattended operation by Northwest's gas control center in Salt Lake City.

All of the gas-compressor equipment was purchased from Solar Turbines, San Diego, utilizing all of that company's models of gas-turbine drivers. The compressor-set control, including surge control, utilized Solar's Turbotronic control system and an Allen-Bradely PLC.

The detailed station design and material procurement were completed by John Brown, Tulsa, for the Solar Mars and Saturn stations, Fish Engineering & Construction Partners Ltd., Houston, for all Solar Centaur stations, and FB&D Technologies Inc., Salt Lake City, for the modifications to existing stations.

Dames & Moore completed the geotechnical investigations for the compressor stations.

Because many of the compressor stations were located in developed areas, special noise-attenuation features were incorporated into the design to meet demands of restrictive state regulations and the close proximity to noise-sensitive areas.

The typical design features included large intake and exhaust silencers, blowdown silencers, modified gas-cooler fans, and dense insulation in the compressor building walls.

Three of the compressor stations-Little Valley, Owhyee, and Winchester-were designed to accommodate Northwest Pipeline's portable trailer-mounted Saturn gas-compressor units that can be easily transported between station sites by road (Fig. 2).

At the new Stanfield Ore., compressor station, all of the facilities to accommodate a portable compressor unit were installed with no permanent compression.

Northwest's two trailer-mounted units are used temporarily to replace compressor equipment that has failed, is down for scheduled maintenance, or, in the case of Stanfield, when compression is required at that site to meet customer requirements.

Typically, they can be set in place, piping and controls connected, and started in just a few hours.

The compressor station construction was completed by six different contractors with each station taking approximately 6 months to complete.

Permits for station construction as well as varied site conditions resulted in unusual construction requirements.

For example, because the best site for the new equipment on Northwest Pipeline's existing Sumas, Wash., station had been designated as a wetland, a two-for-one replacement wetland had to be created. Also, 32-ft pilings had to be installed to support the Sumas Solar Mars unit foundations because of the poor and wet soil conditions.

Another site, Pleasant View, Colo., had a significant archaeological site that needed to be protected before construction could start. At the Mt. Vernon, Wash., site, a special retention pond had to be built to meet the requirements of new storm water run-off regulations.

In order to complete the challenge of commissioning 22 compressor units over a 3-month period, Northwest Pipeline and Solar Turbines established two start-up "SWAT" teams that moved from station to station to complete the basic controls and equipment checkouts and calibration.

Personnel from local operating districts would then complete the purge and packing of the stations and start-up of the facilities.

After start-up was completed, Petrotech, Belle Chase, La., completed a field performance test of the Solar equipment to determine if the equipment met the field performance test guarantee.

Table 3 shows the new compressor stations on Northwest's expanded facilities.

METER STATIONS

The measurement facilities at 57 existing meter stations had to be either completely rebuilt or modified to measure the increased volume. Northwest completed most of the design using in-house staff with assistance from FB&D Technologies.

Many of the station designs could utilize Northwest's standard station modules that consist of a meter skid, regulator skid, and a separator skid. Because of the wide range of flow requirements at the stations, the designs could include any one or combination of positive displacement (PD), turbine, or orifice meters.

At many locations, electronic flow measurement (EFM) was installed using the Fisher ROC flow computer.

The meter stations were constructed by five different contractors: Triad Mechanical, Portland, Ore.; Uribe Inc., Pasco, Wash.; Snelson Inc., Sedro Woolley, Wash.; Udelhoven Inc., Bellingham, Wash.; and Coates Industrial, Salt Lake City.

The meter station (Fig. 3) prefabrication was completed by North American Piping technologies Inc. (Naptech; Clearfield, Utah), Redman Measurement Co. (Tulsa,), and Northwest Pipeline's Vernal, Utah, district.

PIPELINE

The pipeline portion of the project consisted of 362 miles of pipeline loop construction and the requalification of 89 miles of pipeline to operate at a higher pressure. The pipeline facilities consisted of 19 segments in addition to the requalification work and were divided among seven construction spreads (Fig. 4).

The requalification spread consisted of 89 miles of 26-in. main line near Seattle. Population growth in the area had reduced the maximum allowable operating pressure (MAOP) from the original 809 psig to 562 psig.

Through replacement of 3 miles of 26-in. main line and hydrostatic testing of the entire 89 miles, the pipeline was requalified for operation at 809 psig for the northern-most 46 miles and 674 psig for the remaining 43 miles.

The hydrostatic testing had to be divided into 32 test sections because of the variations in terrain. A caustic detergent was used to clean the pipeline before testing so that the test water would be clean enough to discharge onto the ground.

Willbros Butler Engineers, Tulsa, completed the engineering design and procurement for the new pipeline facilities. The company also performed the preliminary and as-built survey for four of the spreads, while the remaining survey work was done by Miller Associates, Salt Lake City, Raleigh & Associates, Portland, and Merryweather Leachman Associates Inc., Bothell, Wash.

CH2M Hill Inc., Salt Lake City, provided the geotechnical services for the project.

Table 4 shows design specifications for the line pipe.

The 20 in., 24 in., and 30 in. double submerged-arc welded (DSAW) pipe was produced by Napa Pipe, Napa, Calif., with 3M fusion-bonded epoxy (FBE) external coating by Energy Coatings Co. (Encoat), Tulsa.

The 24 in. and 20-in. electric resistance welded (ERW) pipe was produced by American Steel Pipe, Birmingham, with 3M FBE external coating by L.B. Foster Co., Birmingham, Ala.

The 6-16 in. ERW pipe was produced by CSI Tubular Products Inc., Fontana, Calif., with 3M FBE external coating by Encoat.

The 16-30 in. ball valves were manufactured by Cameron, 2-12 in. ball valves by WKM, and plug valves by Nordstrom Valves Inc., Sulfur Springs, Tex.

The prefabricated induction bends were manufactured by Naptech. The hot tap fittings used on the project were made by International Piping Services Co. (Ipsco), Broadview, Ill., and T.D. Williamson, Tulsa; hot tap services were provided by TDW Services Inc., Tulsa.

The concrete coating of pipe was completed at the project pipe yards by B.L. Key Inc., Tulsa.

The seven construction pipeline spreads were completed by the six contractors listed in Table 5.

Non-destructive testing (NDT) was performed by Edwards Pipeline Testing Inc., Tulsa; NDT oversite inspection was provided by Bill Miller Inc., Henryetta, Okla.

The construction right-of-way width was typically 95 ft wide for 20 in., 24 in., and 30-in. loops and 80-85 ft wide for smaller diameter loops.

Due to the limited construction widths, ditch spoil was piled over the existing in-service pipeline, which then required careful scrapping over the in-service pipeline during backfill.

Winter construction was required for the irrigated lands of Idaho and Wyoming to avoid interfering with farm irrigation systems and to reduce the potential for breaching one of the large canals.

Heavy snowfalls made construction difficult, but crews continued to work throughout the winter to complete the project on schedule.

A global-positioning system (GPS) as-built survey was completed on Spread 2 by National Pipeline Service, Westerlo, N.Y.

The GPS survey required slightly more time between lower-in and backfill but worked without significant problems and allowed the as-built work to be completed more efficiently.

All bored crossings on the project were made uncased, except where cobble rock necessitated the use of casing. Railroad crossings were installed uncased with 10 ft of cover under the tracks using pipe with extra wall thickness.

A 24-in. diameter by 205 ft long solid basalt uncased crossing of Interstate 84 in Idaho was successfully completed by Western Utilities Inc., Cedarville, Calif., in about 6 days by drilling.

For the longer bored crossings, 60 mils of Powercrete coating was applied over the FBE pipe coating in lieu of 1 in. of concrete coating. This system protected the FBE coating well and reduced the installation time.

Advanced ultrasonic listening leak-detection methods were used during hydrostatic testing when leaks could not be located by excavating.

One leak was located by U.S. Leak Detection Inc South Houston, Tex., by injecting sulfur hexachloride gas into fill water and running a detector over the line to locate the gas. Also, this gas was injected into some segments during initial water filling as a precaution in case a leak was detected.

An electronic gauging pig survey was run on several pipeline segments based on terrain by TDW Pipeline Surveys Inc., Tulsa, and Enduro Pipeline Services & Supply, Tulsa. The survey was run after the hydrostatic test to locate dents, buckles, internal obstructions, and ovality.

The acceptance criteria were 2% OD for dents, buckles, and internal obstructions and 5% OD for ovality. The gauging pig surveys located several large dents which were replaced with pretested pipe before placing the sections in service.

Dew point drying was performed on several new pipeline sections by Pipeline Dehydrators Inc., Houston. The dew point was specified as -38.5 F. which equals 7 lb/MMcf water.

This drying process allowed the pipeline to be put into service immediately without concern for having residual hydrostatic test water create out-of-spec gas or cause hydrate formation in regulators.

Reseeding and relandscaping were provided by several reclamation contractors including Owens Reclamation Inc., Twin Falls, Ida.; Western States Reclamation Inc., Broadfield, Colo.; Terra Dynamics Inc., Seattle; Fox Inc., Milwaukie, Ore.; DK Resources Inc., Lander Wyo.; Kruegers Associated Landscape Inc., Hillsboro, Ore.; and GreenTree Landscaping, Portland, Ore.

ENVIRONMENTAL CHALLENGES

The pipeline project was complicated by numerous environmental and right-of-way mitigation measures and permit stipulations.

In order to identify, prepare, and expedite the hundreds of permit applications, the project required the combined effort of Northwest Pipeline's land and natural resources staff, PIC Technologies Inc., Denver, Power Engineers Inc., Hailey, Ida., and several cultural resource and other environmental contractors.

Several state and county permits were delayed which caused contractor standby and move arounds and added extra costs.

The pipeline segments crossed 70 streams and rivers. Of these, 45 had short construction windows as a result of permit stipulations. This required that separate crews install the stream crossings in advance of the regular pipeline construction.

The pipeline also crossed 6 miles of wetlands, much of which required an extremely narrow 50-ft construction width to comply with permit requirements.

The 4,500-ft wide Columbia River was crossed near Camas, Wash. (Fig. 5), by hydraulic and dragline dredging. A total of 30,000 cu yd of the dredged material had to be loaded onto barges for offsite disposal as a result of low-level contamination by upstream industry and agriculture, which substantially raised the construction cost of this segment.

Idaho specified that all stream crossings be "dry crossings," i.e., flumed or dammed and pumped. This necessitated an innovative technique for the two 50 and 70-ft wide Portneuf River crossings (Fig. 6).

Five 48-in. temporary flumes with removable mid-sections were installed. This installation allowed two of the flumes to be sealed and the mid sections removed to allow excavation under the other three flumes carrying the stream flow.

This process was reversed to excavate under the other two flumes.

COMMUNICATIONS

To provide communications for supervisory control and data acquisition (scada) monitoring and control, Northwest Pipeline's digital microwave communication system had to be expanded to serve the 10 new compressor-station sites.

This required an expansion of the communications backbone system from Evanston, Wyo., south to the Four Corners area in south-western Colorado.

Additional communications links had to be installed to connect the new stations to the backbone network. Communications facilities were installed at 11 compressor station sites, equipment was added at 12 existing communications sites, and 9 new off-system communications sites were constructed.

The communications design, procurement, and construction management was provided by Power Engineers.

Since construction releases for the communication sites were not received until September, weather at the higher elevations was the biggest challenge facing the construction crews.

Of the entire construction, 50% occurred on mountain tops above 8,000 ft elevation. The highest peak, Abajo Peak near Monticello, Utah, was 11,000 ft above sea level and received 300% of normal snowfall during construction (Fig. 7).

Eventually, the U.S. Forest Service shut down the road access because of avalanche danger and the construction was completed using helicopters to transport crews to the site.

MATERIAL MANAGEMENT

The coordination for supplying material to more than 125 construction and fabrication sites was provided through Northwest Pipeline's project administration and purchasing departments and the engineering design firms.

Nine major temporary warehouses and 12 pipe yards were established for distribution of material to the construction sites.

With the goal of minimizing impact, warehouse and pipe yard locations used existing facilities such as vacant pastures and buildings (i.e., truck repair shop), trailers, and some of the construction sites.