HSC Pipeline Work Pushes HDD Envelope.
As reported earlier in Underground Construction, 96 pipeline crossings, owned by 17 companies, their affiliates and the Port of Houston Authority, are being removed or relocated to accommodate a project to deepen and widen the HSC. Authorized and funded by Congress in 1996, the HSC work began in September 1998.
Of the 96 pipeline crossings to be removed or relocated on the HSC, ExxonMobil Pipeline Company of Houston is responsible for installing 26 new (relocated) pipeline crossings and removing a total of 37 existing crossings. A project team made up of five ExxonMobil employees and three contract employees is charged with executing the project. So far, all 26 new crossings have been installed and the company will spend the remainder of this year on final line tie-ins. As to the crossings slated for removal, one 0.5-mile pipeline has been removed and King Fisher Marine is scheduled to begin removing the remaining 36 next year.
It should be noted that the 37 ExxonMobil pipeline crossings designated for removal were installed by trenching prior to the advent of directional drilling technology. For environmental, safety and efficiency reasons, and to meet the minimum -65 feet MLT elevation requirement of the U.S. Army Corps of Engineers, the 26 new crossings were installed by directional drills.
While the directional drilling technique offered distinct advantages, in at least one case, the existing island crossed by the pipelines in the channel area offered insufficient workspace for the drilling equipment needed to relocate the pipelines and for subsequent tie-in operations.
To meet this challenge, the consortium secured permits and King Fisher Marine created an eight-acre work area adjacent to St. Mary's Island. The work area was constructed by placing dredged material behind geotubes filled with dredged material. The island addition, completed in July 1999, provided an excellent base for directional drilling and tie-in operations. Since then, the consortium has been working to install new pipelines through directional drills, complete tie-ins to operating pipelines and remove existing lines by dredging.
ExxonMobil Pipeline Company's Project Manager David W. Beall recently discussed some of the challenges associated with the 26 horizontal directionally drilled (HDD) crossings his company has completed on the HSC. According to Beall, the installation of the new crossings was completed in December of last year.
ExxonMobil's new pipeline installations are concentrated between Alexander Island and Mitchell Point, which is just southwest of the company's Baytown refinery, and the company's pipeline corridor from LaPorte to St. Mary's Island. The work involved installing 23 new pipelines, four through 20 inches in diameter, in ExxonMobil's pipeline corridor from La Porte to St. Mary's Island, and three 10-inch pipeline crossings between Alexander Island and Mitchell point. The pipe selected for the project was XS wall thickness Grade X-42 seamless, except for the 20-inch line, which was XS wall thickness Grade X-52 ERW.
Beall said the entire project, of course, is precipitated by the $500 million Houston-Galveston navigation channel project to deepen the 50-mile HSC from the current 40 feet to 45 (plus) feet, (minimum 47 feet to a maximum of 53 feet in some locations) and widen the shipping lanes from the current nominal 400 feet to a minimum of 530 feet and maximum 780-foot bottom width.
A single bore to pull in three 10-inch pipelines between Alexander Island and Mitchell Point was the first to be completed.
Beall said the Alexander Island location, south of the HSC, afforded Troy's crews enough room for stringing, welding and testing of the three 10-inch pipelines, while Laney's crews set up their drilling rig and equipment spread adjacent to Bayway Drive in Baytown, north of the HSC.
Beall pointed out that the crossing Troy and Laney installed at this location involved a single 3,500-foot directional bore. The initial bore was 8 1/2 inches in diameter, while backreaming enlarged the bore to 36 inches to accommodate the three 10-inch diameter pipelines. Once the bore was enlarged, a cleaning head was run to swab the hole. At that point, the three pipe strings were pulled through the hole.
Prior to the pull-in, all welds were radiographically inspected. The pipe strings were hydrostatically tested before and after being pulled into the hole. A sizing pig was run through each respective pipe string.
HSC Pipeline Work
Throughout the project, ExxonMobil employees Ronnie Lee, Ricky Lloyd and Leonard Hawthorne provided intensive inspection and oversight of all aspects of the pipeline construction activities. Other members of the team included contract hires Monty Lee, Steve Williams and Russell Graves.
Handling the project for the contractors were: Bernie Drane, superintendent for Troy Construction; R.V. (Doc) Reed, superintendent, Laney Directional Drilling; Mike Finster, job superintendent, King Fisher Marine Services and K.C. Yost, project manager, Mustang Engineering.
Laney's crews completed the crossing using an 83,000 pound-rated rig with 90,000 foot-pounds of torque. The bore reached -90 feet below the HSC. This was more than 25 feet below the -65 foot Corps of Engineers clearance requirement for laying pipelines under the HSC to allow deeper draft vessels into the port and for future deepening of the channel.
Once the crossing was completed, tie-ins were made to active onshore lines on each side of the channel. The lines transport nitrogen, crude and refined products. "Of these, the nitrogen line that supplies ExxonMobil's Baytown Refinery and other chemical complex locations in the Baytown area proved to be the most challenging," Beall said. "Since this service couldn't be shutdown, Troy's crews had to make the final line tie-ins without interrupting service."
While recognizing the necessity to protect the pipe coating from being damaged during the multiple line pullbacks, spacers were not used on the lines being, installed. "These devices increase the drag when the lines are pulled through the hole," Beall explained. "They also tend to come loose and wad up, which results in an obstruction and little or no protection of the pipe coating. For this reason, our decision to use a fusion-bonded epoxy, dual-powder coating system on all the new crossings was one of our better decisions."
The Dupont Powder Coatings' NapRock dual-powder, fusion-bond epoxy coating is fused to the pipe. The bottom coating consists of about 20 mils of a normal Nap-Gard Series 2500 corrosion coating. On top of that, a minimum of about 20 mils of Nap-Gard Series 2610 mechanical protection coating was applied to protect the undercoating.
"You never know what the pipe will be rubbing against down hole during a pullback," Beall explained. "With multiple lines, there is always a certain amount of abrasion from the pipes banging and rubbing against each other. That was the purpose of the outer coating, to protect the underlying corrosion coating from being damaged during the final line pullback process."
Beall said they examined the pipe as it exited the bore and found the coating to be in excellent shape.
"We inspected the coating that passed through each hole, and it performed excellently."
St. Mary's Island crossings
The Alexander Island to Mitchell Point crossing proved to be a typical HDD pipeline installation. St. Mary's Island, on the other hand, was somewhat different. At this location, Troy and Laney's crews completed four 48-inch directional drills and installed 23 new pipelines. Hole No. 1 contains four pipelines, (two 12-inch and two 16-inch); Hole No. 2 has seven lines, (two 4-inch, three 6-inch, one 8-inch and one 10-inch); Hole No. 3 has six pipelines (one 4-inch, two 6-inch, two 8-inch and one 20-inch); and Hole No. 4 has six lines (one 4-inch, one 6-inch, three 8-inch and one 12-inch). Installation of the 23 new crossings was completed just before Christmas last year and tie-in to existing operating pipelines is underway. Beall said Troy's crews have been in the tie-in phase at this location since the first of the year.
Once the tie-ins are completed, the pipelines will transport a wide variety of fluids, including crude, refined products, LPGs, ethane, oxygen and various chemicals, such as ethylenes, propylenes and butadienes.
Before tackling the unprecedented directional drilling project at this location, Laney Directional Drilling made a decision to build a new drilling rig for this phase of the project. The hydraulic rack-and-pinion drilling system weighed 49,000 pounds and was designed to provide boring diameters from 12 to 60 inches in diameter and bore lengths up to 6,000 feet.
Beall said, "While we knew the same methods of construction and operation used in more conventional directionally drilled water crossings could be used on this phase of the project, there was some apprehension. Although Laney had made longer crossings and pulled heavier loads, they had never pulled this many pipelines bundled together that weighed this much. The four directional drills involved pulling dead weight ranging from slightly greater than 1.1 million pounds to in excess of 1.5 million pounds."
The HDD technique is commonly used to install multiple pipelines, Beall said. "So, going into this thing we knew it should work but there was still a little doubt in everyone's mind when we looked at the distance and weights involved. In addition, stringing, welding, and positioning the pipe to go in the hole proved quite a challenge for Troy's crews due to the limited space and layout of the ExxonMobil pipeline corridor. However, after the first hole pulled so easily and well under the capacity of the drilling rig, we were confident that we would be successful on the remaining holes."
Although all four HDD crossings were successfully completed, about a quarter of the way into Hole No. 3, the pull head broke.
Beall said this proved to be a minor set back. Specially built dollies constructed from the rear two axles of heavy-haul trailers supported the multiple pipe strings being pulled into the hole. Laney and Troy constructed about 80 of these that were spaced at about 60-foot intervals along the pipeline route to support the multiple pipe strings. As the pipe strings were pulled back through the holes, the dollies rolled to the holes, then were removed and set aside.
The pipe for the project was strung within an ExxonMobil pipeline corridor and extended over a mile from the water's edge. Beall said, "the route of the corridor was, about like a dog's hind leg. Each multiple pipe bundle affixed to the dollies had to roll around a significant corner inside the corridor. In addition, some of the dollies did not track well, and after several weeks of rain, would slide in the mud instead of rolling. During the pullbacks, Troy overcame this by providing heavy equipment over the course of the route and a heavy concentration of equipment at the corner inside the corridor."
When the pull head broke, the pullback process had to be reversed. The pipe string had to be pulled back out of the hole and placed back onto the dollies and moved backward in the pipeline corridor. Beall said things were a little tense, because this likely had never been done before.
Additional equipment had to be brought in and the pullback process was successfully reversed the day before Thanksgiving. Fortunately, Laney got the drill stem back through the hole, the pull head was replaced and the pipe string pulled back through the hole only two days later.
Beall said that despite the many challenges the HDD operations presented, it was without a doubt the safest, most environmentally non-intrusive, and most efficient method of installing the many new crossings. Furthermore, the long-term operability of the new crossings should be much improved.
Removing and relocating the pipelines wasn't the only challenge that made this project unique. With 26 new pipeline crossings that had to be tied into existing operating pipelines located on both sides of the channel, identifying the existing pipelines with no point of reference posed a problem. "There are multiple eight-inch, six-inch and four-inch lines out there that had to be identified before final line tie-ins could be made," Beall said.
Conventional electronic methods of locating pipelines were not adequately reliable a mile across the water due to interference and the possibility of the lines being shorted to each other. "We worried about this for sometime before we came up with a way of positively identifying the existing lines," he said. "Finally, we came up with two techniques. One was to clamp a sonic flow meter onto the pipeline on one side of the channel and a second flow meter on what we believed to be the same pipeline on the other side of the channel. Next, we would vary the flow in the line up and down. If the flow profile of the two meters was the same, it confirmed that it was the same pipeline."
The only problem with this method is that the sonic flow meters only worked well on liquid pipelines. This precluded use on an oxygen line and several ethylene lines.
Quite by accident, an even better way was found to identify the correct line. Bernie Drane, Troy's superintendent, mentioned that another client sometimes uses strain gauges to make sure they are on the correct line prior to a tie-in. ExxonMobil's Project Engineer Dan Behringer took this idea and developed a method that allowed positive identification of the existing pipelines on both sides of the channel.
"The strain gauges provided a simple solution that worked extremely well," Beau said. "We put a strain gauge on each existing pipeline on each side of the channel. Hoop strain was recorded while the pressure in the pipeline was varied. The strain data was downloaded to a PC, and a unique strain rate (strain vs. time) profile was plotted for each strain gauge. If both strain gauges were on the same pipeline, the strain rate profiles are typically identical, or very nearly so, allowing us to confirm it was the same line."
According to Beall, the 23 pipelines will be tied in and in service by late this year or early next year. The tie-in schedule is fixed to accommodate pipeline customers to the maximum extent possible,
In retrospect, Beall said, "I don't think there has ever been a pipeline project quite like this one. It's certainly the most unique project I've ever been involved with during my career. While it's proven to be both challenging and interesting, it has also been a lot of fun. The project is definitely a testimony to the near flawless execution that can be accomplished when people work together as they should."
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