Thread Content
Regarding the scheme of using sleeves for pipeline crossings under railways, after referring to domestic and international standards and conducting a comprehensive analysis, 20 points have been summarized below; members of the forum are welcome to provide their feedback. 1. Conveyance pipes that use sleeves for passage must meet the material and design requirements specified in ASME B31.4 or ASME B31.8. 2. Materials suitable for use as sleeves include new or used pipes, as well as pipes that are rejected during steel rolling processes. 3. The inner diameter of the casing should be large enough to accommodate the delivery pipe, provide adequate insulation for maintaining cathodic protection, and prevent external loads from being transmitted from the casing to the delivery pipe. The nominal diameter of the sleeve should be at least two sizes larger than that of the delivery pipe. 4. The minimum nominal wall thickness of the steel casing used for drilling penetration shall be greater than or equal to the values specified in Appendix C. 5. The casing should be free of obstructions; straight pipes should be used as much as possible, with a uniform bedding throughout the entire length of the penetration. 6. Use drilling to install the casing, and the excess of the drill hole diameter should be kept as small as possible to reduce the gap between the casing and the surrounding soil. 7. The steel sleeves should be fully connected to ensure that the pipeline in the crossing section is continuously protected from start to finish. 8. At the location where the sleeve is installed, its end shall extend at least 600 mm beyond the foot of the slope or the subgrade, or at least 900 mm beyond the bottom edge of the drainage ditch – whichever value is greater. 9. The angle between the crossed railway and the crossing pipeline should be as close as possible to 90 degrees, but in any case it should not be less than 30 degrees. 10. Try to avoid crossing in humid or rocky areas as well as in places where deep digging is required. 11. The vertical and horizontal clear distances between the pipeline and the structures or facilities surrounding it must meet the requirements for the maintenance of both the pipeline and those structures or facilities. 12. The sleeves under the railway track shall be installed with a minimum cover layer as specified (the distance from the top of the sleeve to the surface of the railway bed); for pipelines carrying volatile liquids, this minimum cover layer is 1200 mm. If the specified minimum coverage layer cannot be achieved, enhanced protective measures should be taken. 13. The conveying pipe installed in the sleeve should be provided with appropriate support, insulation, or other means to prevent it from coming into contact with the sleeve, ensuring that no external loads are transmitted to the conveying pipe after installation. It can also be accomplished by using a method of accumulating layers of coating and external wrapping bands to form a ring, or by using a concrete jacket. When pre-made insulators were used at that time, they should be arranged evenly and firmly fixed to the conveyor pipe. 14. In cases where there are constraints at the construction site, structural difficulties arise, or special requirements exist, multiple delivery pipes can be placed inside a single sleeve. Its installation shall comply with the above provisions and shall ensure that the delivery pipes are insulated from one another, as well as from the sleeves. 15. The ends of the casing should be sealed to reduce the intrusion of water and surrounding soil particles. It should be recognized that a complete water seal cannot be achieved under field conditions, and water infiltration must be anticipated. Both ends of the sleeve should be sealed with putty-like material to prevent water channels from forming through the sleeve. 16. It is not required to install a vent on the casing. 17. If vent pipes are to be used, 1 or 2 such pipes shall be installed; the diameter of these vent pipes must be at least 51 mm. They should be welded to the casing, and extend above the ground level at the road boundary or fence. Before welding the vent pipes to the casing, holes must be made in the casing, with a diameter that is at least half of the diameter of the vent pipes. 18. The length of the vent pipe extending above the ground surface shall be not less than 1200 mm, and an appropriate rain cover shall be installed at the top of the vent pipe. 19. By installing an annular insulator, the sleeve does not come into direct contact with the conveyor pipe, thereby achieving electrical insulation. The insulator should be designed to minimize the supporting pressure between it and the pipeline coating. 20. Supervision and inspection should be carried out during the crossing construction period. Before installation, an inspection for visual defects should be carried out on the sections of the conveyor pipe where it passes through various structures; all ring welds must be inspected using X-rays or other non-destructive methods. After the casing penetration installation is completed, tests should be conducted to verify the electrical insulation between the transmission pipe and the casing.