The pipeline experience in North America is noteworthy

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The pipeline experience in North America is worth noting—written on the occasion of the commencement of the Second West-East Gas Pipeline Project. On January 11 this year, amid extremely tight winter gas supply conditions, Valve Room 111 of the West-East Gas Pipeline had to be shut down for repair due to air leakage at the flange connecting the bypass ball valve on the upstream side to the main pipeline. This reminds one of some suggestions put forward by the supervisory headquarters for the West-East Gas Pipeline project, Universal Ensco, Inc., which stated that, based on pipeline experience in North America, \"it is standard practice in that region to connect valves and pipelines using welding instead of flanges; this is done to ensure that high-pressure gases and the pipeline systems as a whole remain within sealed metal containers, thereby preventing potential leaks at the flanges.\" What is concerning is that all the ball valves connecting the bypass lines adjacent to the 138 valve chambers of the West-to-East Gas Pipeline main line to the main pipeline are flanged connections; over time, the probability of leaks at these flanges will increase, and the flanged connection points will remain permanent sources of risk. The North American experience introduced by Universal Company deserves our close attention. As is well known, North America is one of the regions in the world with the richest natural gas resources and the highest consumption of natural gas. The construction of the first natural gas pipeline in the United States began in 1872, and it is now over 130 years old. By the early 1990s, North America had a total of 535,000 km of natural gas transmission pipelines, accounting for 38% of the world’s total of over 1.4 million km of such pipelines. Of this amount, the United States had 458,000 km, Canada had 64,000 km, and Mexico had 13,000 km. Out of the world’s 554 underground gas storage facilities, 424 were located in North America, representing 76% of them. In 2005, the world produced 2.76 trillion cubic meters of natural gas, with the United States alone consuming 633.5 billion cubic meters, accounting for 33% of global consumption. Thanks to the long history of pipeline construction and the large scale of such projects in North America, along with comprehensive regulatory standards for pipeline safety, this region has accumulated extensive experience in pipeline construction and operation. Recently, the construction of Line 2 of the West-East Gas Pipeline Project, invested in by CNPC and spanning a total length of over 9,000 kilometers across 14 provinces, autonomous regions, and municipalities, has begun. On this occasion, it is worth revisiting some suggestions put forward by American Global Engineering Company in 2006 regarding the construction of gas pipelines in China, in the hope of drawing the attention of colleagues: 1. Cyclone separators are not necessary at distribution metering stations. In North America, as long as pipeline cleaning and drying meet the specified requirements, and the metering equipment used to receive gas into the pipeline is equipped with systems to prevent liquids from entering the pipeline, there is no need to install both cyclone separators and filter separators at distribution metering stations. In China, cyclone separators and filtration separators are installed at all distribution metering stations. Universal Company of the United States recommends installing only filter separators at the distribution metering stations. 2. There is no need to build main valve chambers (houses). In North America, the main valves of gas transmission pipelines are buried underground, without the use of enclosed structures. Sealed valve chambers are often considered hazardous areas where natural gas can accumulate, as well as places where water, moisture, and insects or animals gather – all of which hinder the safe operation of pipelines. To ensure the safety of the valves, fences are usually used and the gates are locked. In the West-East Gas Pipeline project, brick-built structures were constructed around the main valves to enclose the equipment. This not only creates safety issues but also requires the installation of unnecessary natural gas detection equipment. Universal Company of the United States recommends: do not build valve chambers on main lines. To ensure the safety of the valves, walls or fences can be built, and the gates can be locked (this measure is not suitable for China’s conditions, per the author’s note). 3. Welded valves on pipelines: In natural gas pipelines in North America, it is industry practice to connect valves to pipelines by welding, in order to avoid using flange connections. Because once a flange leaks, the pipeline must be shut down to repair the leak. This ensures that the high-pressure gas and the piping system are all enclosed within metal containers, up to the first insulation node of the system. Industry practice also ensures that flanges are not used on the Supervisor lines, thereby avoiding potential flange leaks. In the West-to-East Gas Transmission project, a flange connection is installed on each side of the pipeline for the two vent valves at every main valve. Once the gasket at the connection leaks, the pipeline must be shut down and the entire pipe section drained in order to repair the leak. Universal Company of the United States recommends that all valves connected to the pipeline be welded on the same side of the pipeline. 4. Maximum allowable operating pressure of branch pipelines: In North America, in recent years, the pressure in the branch pipelines of gas transmission lines has been designed to be the same as that in the main pipelines, and these systems have been tested. This design eliminates the need to install expensive and unnecessary voltage regulation equipment at the junction of the branch lines and the main line. It is particularly important that such a design can utilize the \"pipeline filling volume\" to meet the peak demand for gas in branch lines. Furthermore, should market conditions change or if there is a need to supply new users in the future, this design also provides room for the development of additional natural gas capacity. It should be noted that to meet this design requirement, capital costs must be increased in order to raise the ANSI (American **Standards Association) ratings of the flanges and valves, as well as those of the pipelines. However, many pipeline systems have shown that these costs are negligible compared to the profits resulting from a higher design pressure for the pipelines. In the West-to-East Gas Pipeline project, the design pressure of the branch pipelines is lower than that of the main pipeline, which requires the installation of additional pressure reduction stations at the junctions between the branches and the main pipeline. This limits the amount of gas that can be supplied through the pipelines during peak hours, as well as limiting the potential to attract new customers in the future. Universal Company of the United States recommends that the design pressure of branch pipelines should be the same as that of the main pipelines. 5. Selection of anti-corrosion patching materials: In large-diameter pipeline projects in North America, pipeline companies do not use shrink sleeves for on-site anti-corrosion patching, as it is difficult to install them. They generally use relatively simple anti-corrosion coatings for welds, such as liquid epoxy coatings and polyurethane coatings. In the West-to-East Gas Pipeline project, the client required the use of shrink sleeves for anti-corrosion sealing. To meet regulatory requirements, the construction party continuously encounters problems when using shrink sleeves. Universal Company of the United States recommends that, in future large-diameter construction projects, liquid coatings to be used for anti-corrosion patching on site should be researched and selected. It is particularly important to note that Universal Company of the United States recommends against using shrink sleeves in horizontal directional drilling. 6. Reduce the number of hot-bent bends. In North America, due to the requirements for thick-walled steel pipes and the additional costs associated with the production, testing, corrosion protection, and shipping of hot-bent bends on-site, contractors try to minimize the use of such bends in pipeline projects. Hot-bent pipes mainly increase the number of joint welds, and manufacturers also require a longer delivery time. For the design of vertical bends, the earthwork can be adjusted accordingly, and on-site bending can be employed. For the design of horizontal bends, direction can be changed at most locations using multiple on-site bends. In the West-to-East Gas Pipeline Project, as mentioned above, after reviewing the design, the owner permitted a higher proportion of field cold-formed pipes to be used in place of hot-bent pipes. According to Universal Company of the United States, since important hydraulic protection measures have been installed in certain areas of the loess region, it is necessary to consider minimizing earthwork and rockwork operations. Universal Company of the United States recommends that, in future pipeline projects, before specifying heat-bent elbows, a detailed design for such elbows should be developed in collaboration with contractors who have experience in constructing projects similar to West-East Gas Pipeline, including on-site inspections of all locations where heat-bent elbows will be used. 7. Design of mainline valves: In most Western countries, natural gas is discharged directly into the air through vent valves, without the need to feed it into a flare for combustion. Using a vent flare system increases the cost and difficulty of installing the main valve. Additionally, there is an additional vent valve on the vent line of the main valve, which is not present in North American designs. In addition, it is not allowed to connect small-diameter pipelines to the main pipeline, as if such a small pipeline leaks or ruptures, the main pipeline will need to be drained for repair. Universal Company of the United States recommends that: a) if permitted by Chinese law, the use of vent stacks and flare burners should be eliminated in remote, sparsely populated areas, and natural gas should be released directly into the atmosphere. b. The diameter of the pipeline on the side connected to the main line vent valve should be at least 2 inches; this pipeline is equipped with a shut-off valve, and it should be welded to the shut-off valve on its corresponding side. All other connected gas pipelines should be led out from the opposite side of the connection to that 2-inch diameter pipeline. During pipeline operation, this isolation valve can be locked in the open position. C. Remove the excess valves on the vent line that lead to the vent flare. 8. Structural supports welded directly to the pipeline: International regulations and standards governing pipeline construction do not permit structural supports to be welded directly to pipelines, unless in special cases it is necessary to reinforce operating equipment or install plates. In the West-to-East Gas Pipeline project, the structural supports are designed to be welded directly to the pipelines they span. Universal Company of the United States recommends that, in future pipeline projects, structural supports should not be designed to be welded directly to the pipelines. 9. Technical requirements for hydrostatic testing: In North America, pipe manufacturers are required to ensure that the steel pipes they produce achieve a minimum yield strength of 100%. After completion of construction, steel pipes manufactured by many companies can achieve a minimum yield strength of 100% or even 110% in hydrostatic tests, which is the standard practice in the industry. Under normal circumstances, the minimum testing pressure shall not be less than 92% of the minimum yield strength. This is widely accepted, as pipes made of steel are generally thicker than the specified thickness, and the actual yield strength of such pipes is always higher than the specified minimum yield strength (SMYS). Furthermore, the length of the pressure testing section for large-diameter pipelines is generally limited to around 30 kilometers, but it can be longer if conditions permit. Taking into account the regional classification, as well as the wall thickness of the steel pipes and the grade of the steel, the pressure difference should be limited such that not only is the minimum testing pressure met at the highest point, but also the maximum allowable testing pressure is met at the lowest point. On the pressure testing pipe sections limited by elevation differences and testing pressures, using thick-walled steel pipes over short distances in areas with lower elevations allows for pressure adjustment, thereby significantly reducing the number of such pipe sections. In the West-to-East Gas Pipeline project, the maximum length and maximum height difference specified in the standards are unreasonable for large-diameter pipelines and mountainous areas. In some mountainous areas, the use of grade 1 and grade 2 steel pipes in lower elevation areas increases the number of pressure testing sections. Universal Company of the United States recommends that when designing future pipeline projects, the regional zoning, elevation levels, and water supply conditions should be examined in order to determine the locations for pipes of different thicknesses and grades, thereby minimizing the number of pipe sections that need to be pressure-tested. In addition, Universal Company also recommends that the steel pipes produced by pipe manufacturers should achieve a minimum yield strength of at least 100% in tests, as well as a minimum yield strength of 100% that is equivalent to that of existing pipelines. 10. Site selection for mainline valve rooms and stations: In North America, when selecting sites for mainline valve rooms and stations, site selection criteria are generally applied. Factors to be considered include convenient transportation, easy access to utilities, the nearby residential population and terrain, avoiding floodplains, etc. In addition, the regulations and requirements** must also be taken into account. In China, many mainline valve rooms and stations face problems due to floods, poor access roads, and proximity to unstable slopes. Universal Company of the United States recommends that site selection criteria be established for all main valve rooms and stations, with these criteria specifying the surrounding terrain conditions as well as the minimum elevation requirements, which must be followed. 11. Changes in design pressure for station facilities: In North America over the past few years, the natural gas process pipelines at metering stations and pressure reduction stations have been designed to meet the highest design pressures required by those stations, and they have undergone testing. Even if the pressure is reduced, pipelines, valves, and fittings should still be designed, constructed, and pressure-tested according to the highest design pressure. Such a design not only eliminates the need to install safety pressure relief valves, avoids additional hydrostatic testing, and prevents extra welding of steel pipes of different grades and wall thicknesses, but also makes it easier to maintain and operate the pipeline facilities. These benefits far outweigh the additional costs associated with higher-grade valves, pipelines, and fittings. In the West-to-East Gas Pipeline Project, the natural gas process pipelines at the metering stations and pressure reduction stations have four different pressure levels within a single facility; this requires multiple pressure testing sessions as well as the installation of numerous safety pressure relief valves. Universal Company of the United States recommends that all pipelines in metering stations and pressure reduction stations use the same design pressure. 12. Station design issues 12.1 Review of the design by construction and operation personnel It is industry practice in large-scale projects for experienced construction, operation, and maintenance personnel to review the preliminary design and layout plans of the station, in order to identify construction and operation-related problems and make modifications to the design accordingly. In the West-East Gas Pipeline project, American Global Company believes that no review was conducted on the construction and operation of the station facilities prior to construction. Universal Company of the United States recommends scheduling time, prior to finalizing the design, for construction and operation personnel to review the preliminary design and layout plans of the facility. 12.2, Connection of branch pipes: In North America, short pipes are not welded directly to high-pressure gas facilities, as these pipes generally cannot be welded thoroughly and are prone to breaking under vibration. As per the regulations, fittings should be used to reinforce the weld joints; these fittings include tees, saddle-type bosses, threaded bosses, and welding bosses, in order to ensure that the branch lines achieve maximum mechanical strength. Most pipeline companies have design guidelines and technical requirements for all branch connections. In the West-to-East Gas Pipeline project, straight-welded short pipes were used on the high-pressure gas pipelines. Universal Company of the United States recommends using fittings with reinforced welds for all branch connections. Furthermore, Universal Company recommends that, in future projects, design guidelines and technical requirements be established for all branch connections. 12.3 Valve handwheels and actuators: In North America, pipeline operating companies generally specify that the optimal safe working height for operating and maintaining all valves, equipment, and instruments is around 1.2 meters. In the West-to-East Gas Transmission pipeline project, the heights of the operating and maintenance equipment, valves, and pipelines at various stations vary; some are very low while others are quite high. (The safety valves on the distribution pipelines at the distribution stations are installed on above-ground pipelines, with a height of 2.7 meters, which makes maintenance difficult. The situation is somewhat better for the distribution pipelines on the Ji-Ning line, where the safety valves are installed on buried pipelines, but their height is still 2 meters, according to the author.) Universal Company of the United States recommends that, in the design of future pipeline systems, this height be standardized, and the pathways leading to valves, equipment, and instruments be shortened as much as possible. 12.4 The pressure used for testing the separator is lower than that used for testing the facility as a whole. In international engineering projects, it is standard practice to test all facilities, including those that have been manufactured and tested by the manufacturer, to ensure that they are all subjected to the same testing pressure. For stations, the pressure used for testing is generally 1.5 times the design pressure. In the West-to-East Gas Pipeline project, when testing the cyclone separators and filter separators for pressure, the pressure reached did not reach 1.5 times the design pressure. Therefore, when conducting hydrostatic tests on the station, the testing pressure for them is 1.25 times the design pressure, and they must be tested separately from the rest of the station’s equipment. Universal Company of the United States recommends formulating technical specifications for support points, requiring manufacturers to achieve the same testing pressure as that used at the facility when testing the equipment intended for use there. 12.5 Standardization of metering equipment for closed-transmission systems: In Alliance pipeline projects, the metering equipment used in natural gas closed-transmission systems has been standardized, with only one type of metering device being employed – ultrasonic meters. Since the Alliance pipeline is a new type of pipeline system, it was decided initially to use only one type of metering equipment in order to reduce operating and maintenance costs, as well as to simplify the operation of the pipeline system by eliminating the need to operate and maintain other types of metering equipment. In the West-to-East Gas Pipeline project, the pipelines are equipped with both ultrasonic metering devices and turbine metering devices. Universal Company of the United States recommends that designs should be standardized, and only one type of sealed conveying metering device should be used in pipeline systems. 12.6 Vent flares at metering stations In North America, it is not required to install vent flares at metering stations. Since the vent flare can only vent a small amount of natural gas, this gas can be directly released into the atmosphere. In the West-to-East Gas Pipeline project, vent flares are installed at all metering stations. Universal Company of the United States recommends that vent flares are not required at metering stations. 12.7 Separators in pigging stations In North America, especially in the ALLIANCE pipeline projects, strict technical specifications must be established before cleaning and drying natural gas pipelines. In accordance with this requirement, intermediate separators are not needed at pig stations and some compressor stations. In the West-to-East Gas Pipeline project, there are only two natural gas sources: Lunnan and Jingbian. As long as appropriate separation equipment and monitoring facilities are used, moist or unclean natural gas will not enter the pipelines. Furthermore, as long as the main lines of the West-to-East Gas Pipeline Project are properly cleaned and dried, there should be no impurities or residual liquids left in the pipes that have been cleaned and dried. Unless it is anticipated in advance that the pipeline will be used to transport wet natural gas or unclean natural gas. Universal Company of the United States recommends not installing intermediate separators at every pigging station. Furthermore, strict evaluation should be conducted on the separators that need to be installed at the compressor station. 12.8 Steel pipe supports on the ground: In North America, it is standard practice to install steel pipe supports beneath the pipes, rather than beneath the valves; this design allows for easy movement of the valves when maintenance is required. Furthermore, adjustable steel pipe supports are used; if the concrete foundation settles, the settlement issue can be addressed by adjusting these steel pipe supports. In the West-to-East Gas Pipeline project, the steel pipe supports are installed below the valves, rather than below the pipes. Universal Company of the United States recommends that pipe supports should be installed beneath the pipes, rather than beneath the valves, and that adjustable pipe supports should be used. 12.9 Underground Cables When installing cables in underground ducts, it is standard practice to place the cables within cable sleeves or conduits to provide mechanical protection. In addition, concrete protective plates are laid over medium-voltage and high-voltage cables, and underground marker strips are placed over underground cables and conduits to further prevent the cables from being accidentally dug up. In the West-to-East Gas Pipeline project, the cables are buried directly in underground trenches, without the use of conduits, protective plates, or marker strips. Universal Company of the United States recommends that, to provide further protection for the cables, they should be installed in protective sleeves, along with concrete guards and/or marking strips. 13. Fiber optic conduits installed together with pipelines In North America, fiber optic conduits or cables are not installed simultaneously with large-diameter long-distance pipelines. The main reason is the high labor costs in pipeline projects in North America. If installation is necessary, it can be carried out later by a small crew near the pipes, which will not be costly. In addition, when excavation is required for reasons such as pipeline maintenance and repair, the fiber optic cables installed above the pipelines also pose a barrier to equipment installation. Furthermore, due to the high installation costs of fiber optic conduits and the damage to fiber cables in urban areas caused by exposed conduits, it has proven that using satellite communication systems on pipelines is more cost-effective and reliable. Universal Company of the United States recommends that, in future pipeline projects, the advantages of installing communication fiber optic conduits should be determined through thorough cost-benefit analysis. 14. The distance between pig stations can be greater. The distance between pig stations depends on the service life of the battery pack in the intelligent pig. If the pipeline operates at a speed of 3 to 5 meters per second, then the distance between pigging stations is around 250 miles (400 kilometers). In the West-East Gas Pipeline project, there are many intermediate pigging stations that are less than 200 kilometers (120 miles) apart. Universal Company of the United States recommends that, in future pipeline projects, the distance between pigging stations should be designed to be greater. 15. Reduce the number of pipelines at stations: In the West-East Gas Pipeline Project, most stations have four pipelines equipped with vertical separators and cyclone separators. For reasons of reliability and maintenance, backup pipelines are necessary, but only two or three large-diameter pipelines are required. The fewer pipelines, valves, and separators used, the more costs can be saved. Universal Studios USA recommends reducing the number of pipelines in future facility designs. 16. Reducing the outlet temperature of compressor stations: In the West-East Gas Pipeline Project, the maximum outlet temperature of natural gas entering the pipelines downstream of the compressor stations was set at 60°C; this required high-temperature resistance and anti-corrosion treatment to be applied to the pipelines located about 50 kilometers downstream of the compressor stations. Furthermore, in addition to cooling the cycle air, the compressor station is not equipped with a natural gas cooling unit. Once the West-to-East Gas Transmission project has cooling devices installed at all compression stations and is operating at the designed flow rate, hotter gases require more compression and higher fuel consumption. Universal Company of the United States recommends that, in future pipeline projects, the natural gas outlet temperature at compression stations be limited to 50 degrees Celsius.