Pipeline project requires varying construction techniques.
Exxon's project manager D. W. Beall indicated the aim of the project was to double the average product carrying capacity between Exxon USA's Baytown Refinery and Exxon Pipeline's Pasadena station.
Continuing, Beall said Exxon's Pasadena facility receives various grades of gasoline and distillates, including auto diesel and aircraft turbo fuel, from the Baytown facility and plans to move JP-8 fuel for the military in the future. These products are transported through an existing 16-inch diameter products line. By laying a new line from Baytown into Pasadena paralleling the existing line it would be possible to separate the products. "We'll be putting the distillates in the 16-inch line and the gasoline in the newly built 12-inch line," he said, "which will pretty much double our average capacity."
Beall noted that the route of the new 16-inch directionally drilled bay crossing extends from the Baytown Refinery to just over a mile across Scott Bay where it makes landfall on St. Mary's Island at the northern edge of the Houston Ship Channel. From here, the line is tied into an existing 16-inch spare that runs (north to south) from the island across the Houston Ship Channel and Houston Lighting & Power's effluent canal. The remainder of the route runs from the southern most end of the spare line to the Pasadena location. "This final segment," Beall said, "required about eight miles of conventional 12-inch land lay."
Rogers & Phillips which opted to utilize its own crews to carry out most of the land lay portion of the job, sub-contracted five directional drills (9,438 feet) and 17 slick bores (2,320 feet) required on the project to Laney Directional Drilling Co., Houston.
According to Rogers & Phillips' executive vice president Bill Phillips, work on the project commenced at the island location.
Phillips said that although Exxon owns the island, 30 or more pipelines crisscross the area that are owned by Exxon as well as a number of other companies.
In describing the work, Phillips noted that all the materials needed to mitigate island erosion had to be delivered by barge. "At one point," he said, "we had four barges and two tugs on location."
During this phase, he continued, crews placed 2,350 tons of rock and 3,000 cubic yards of clay fill over a three-week period.
5,326 Foot Directional Bay Crossing
As work on the island progressed, equipment was assembled in preparation to begin the 5,326-foot directionally drilled crossing across Scott Bay from Baytown to St. Mary's Island.
Laney Directional Drilling Co. vice president Dickey Laney said entry and exit pits and heavy equipment spreads were assembled on both ends of the crossing, with deployment of the equipment spread in Scott Bay charged to King Fisher Marine, Port Lavaca.
In all, five barges were assembled on the west side of the island. The barge mounted equipment spread included a 750,000 pound drilling rig, four trailer loads of drill pipe, a mud pump, mud mixing tanks, plus fresh water for mixing the drilling slurry.
Also in this phase, crews with King Fisher Marine drove piling to secure the barge carrying the drilling rig which would have to remain in stable position throughout the crossing.
In other preparation work, steel stakes were set out in precise positions in Scott Bay marking the designated pipeline route the directional crossing would follow. These would later serve to help guide the bent-sub assembly that would be attached in front of the drill pipe to steer the pipe during the cutting of the pilot hole and keep it on course.
In preparation work onshore, Laney's crews were also busy assembling an equipment spread on the east side of Scott Bay. Among the larger equipment items was a second 750,000 pound drilling rig, a backhoe and side boom tractor with cradle type rollers to position and support the pipe being pulled into the hole.
Also in conjunction with this phase, crews with Rogers & Phillips were pressed into service to find sufficient space to string the 5,326 foot products line in preparation for the pull.
"Ideally," Phillips said, "the pullback process during a directional drill is continuous. However, sufficient space did not exist to fabricate the pipeline in a single string. The only alternative method was to weld up the line in two 2,660-foot-long sections along the shoulder of Bayway Drive in Baytown."
"When the rig started pulling the pipe into the hole," Phillips continued, "crews backed one section of the line up as far as they could and started in the hole with the other section. When the two ends came together the pull was halted to allow crews to weld the two sections together and complete the pull."
"We were fortunate to have the necessary equipment to expedite the crossing, "Laney explained. "By using two rigs," he said, "we were able to drill an 8-inch pilot hole from the land side to the island and then cut back with a 28-inch cutter. The land based rig, was then moved out of the way to allow the barge mounted rig to pull a swab and the pipe at the same time."
"The crossing that required a 35 [degrees] bend in the first 500 feet of pipe and reached a full 65 feet below the floor of Scott Bay kept crews busy around the clock for eight full days," Laney said.
As quickly as the pipe surfaced, Gene Rogers, president of Rogers & Phillips and project manager on the job, took over to tie-in the new pipeline to the existing 16-inch spare line which crosses the Houston Ship Channel.
The tie-in required a nine-man crew working on the island and aboard barges and tugboats for approximately a week. In addition to tough ground conditions, Rogers said they were forced to contend with fog and low tides which complicated the transport of crews back and forth to the island every day.
The equipment mobilized to the island location included an excavator equipped with a 60 foot arm-approximately twice the length of a conventional unit-plus two skid mounted welding machines. In addition, an 80-ton crane was operated from the deck of one of the barges to facilitate pipe handling operations.
As noted by Rogers, a long reach excavator was needed to accommodate trench work required on the island which reached depths up to 11 feet at some locations. Also, in order to tie-in to the existing 16-inch line, three 13-foot radius hot bends were used.
8-Mile Land Lay
For the most part, the land lay portion of the job required the new 12-inch line to be installed along the same route as the existing 16-inch products line. "This was the only route available between the two facilities," Exxon Pipeline's Beall explained. "By paralleling the existing line we were able to use a good portion of our own pipeline corridor, as well as those of Shell, Rohm & Haas and Occidental."
"That's another thing," he said. "Since crews were forced to lay a good portion of the line within foreign corridors, it was also necessary to locate the line at the precise horizontal and vertical locations designated by owners of the respective corridors."
Beall noted that the need to closely adhere to these easement specifications prompted Exxon to keep a surveyor on site at all times. "In some pipeline corridors along the route," he said, "lines were located so closely crews could not get a trackhoe bucket between them."
Roger & Phillips project superintendent Paul Reyes, charged with overseeing the land lay portion of the job, said the pipe stringing crew was among the first to arrive. "Although the ground was wet and we were having to string off rolligons, the entire eight-mile section was completed in about two weeks," he said.
The main line ditching crew that followed remained on site for about four weeks. "Since we were continually crossing high pressure pipelines and working in foreign corridors," he said, "this was not a fast paced job."
Instead, safety was far more critical. The job required an estimated 110 foreign pipeline crossings. There was also extensive use of trench shoring boxes and sheet piling to ensure the safety of workers in congested areas and adjacent to railroads, roadways, etc.
Work during the trenching phase was challenging as well. Although the contract specified four feet of cover, in areas where foreign lines were encountered the cover was often much deeper. Along many of the corridors crews encountered anywhere from 12 to 20 existing lines. Reyes said trench work in these areas reached eight to 12-foot depths.
Also during the land phase, crews with Laney Directional Drilling completed four directional drills and 17 slick bores totaling over 6,400 feet.
Of the four directional land drills, two posed special challenges.
The longest of these involved a 2,100 foot directional drill adjacent to an industrial business park. And, since the existing pipeline corridor here runs right through the parking lots, ditching the line was not an option.
"We were at a real disadvantage going in," Laney said, "because these owners had already had a bad experience with another contractor who had unsuccessfully attempted a directional drill at this same location several years earlier."
"For this reason," he said," the directional drilling depth at this location reached 50 feet." While much deeper than necessary, crews used less pressure and pulled the pipe slower in order to eliminate any problems with mud seepage.
Laney's crews exercised the same precautions in completing a 581-foot crossing of the Port Terminal Rail Authority (PTRA). Not only was this the first directional drill permitted under existing PTRA tracks, representatives with both Exxon and Laney spent several months discussing the crossing with the Port of Houston Authority before permission was forthcoming.
"As anticipated," said Laney, "no mud problems occurred at these locations or on any"other portion of the job."
Although contract terms called for Rogers & Phillips to complete the job on March 1, it was actually completed in mid-February, almost two weeks ahead of schedule.
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|Publication:||Pipeline & Gas Journal|
|Date:||Jun 1, 1996|
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