Anchor Flanges for the East-West Gas Transmission Project

This paper analyzes and improves the original anchor flange structure used in domestic and international pipeline project designs, considering the relevant requirements for anchor flanges in the East-West Gas Transmission Project in Sichuan. A new type of staggered flange structure is proposed, which is welded using ring forgings and pipeline steel pipes and is designed for easy on-site welding construction. To adapt to the development trends in pipeline steel, it is proposed that the material composition of the anchor flange forging ring be aligned with the chemical composition of the connected main pipeline material. Bending and water pressure tests on the first batch of trial-produced anchor flanges proved that the new anchor flange meets the design requirements of the East-West Gas Transmission Project in Sichuan and effectively ensures the project's construction needs.
 

The East-West Gas Transmission Project in Sichuan is a major initiative of the Sinopec Group and an essential part of China's "Eleventh Five-Year Plan." It begins in Dazhou City, Sichuan in the west and ends in Shanghai in the east. It forms an important part of China’s natural gas pipeline. Upon completion, the project will help alleviate the imbalance in natural gas supply and demand in eastern China.
 
An anchor flange is a crucial pipeline engineering component, indispensable for connecting pipelines. It is primarily used in tunnel crossings, gas transmission stations, and pipeline segments. It is cast with cement to form an anchor pier that secures the pipeline, prevents displacement, and ensures the safety of natural gas transportation. Currently, two structural types of anchor flanges are designed and used in China: the first involves welding the outer circumference of the steel pipe to reinforce the pipe clamp, with a ring flange plate, rectangular ribs, and triangular ribs welded outside the clamp. This type is primarily used in oil pipelines. This anchor flange design has numerous welding seams and significant stress concentration. Sharp corners on the rib plates cause the anti-corrosion layer to not adhere firmly, leading to frequent detachment and reducing the flange’s service life. The second type is a simple ring forging structure. In long-distance pipeline construction, welding involves complex climatic and geographical conditions, high construction mobility, all-position welding operations, and varied welding processes. However, construction teams cannot select an ideal site, increasing the challenges of managing construction, quality, and safety compared to factory-produced components. Environmental factors such as wind, rain, temperature, and humidity can impact welding quality. Experience has shown that this type of structural anchor flange has the following disadvantages:

 

Design an anchor flange with a ring forging and sleeve welding structure, meaning it is welded from a ring forging and a steel pipe for the pipeline. The structural size of the ring forging is determined by factors such as the regional grade of the pipeline, internal pressure, design temperature, and the yield strength of the ring forging material. The length of the sleeve is determined based on the size of the line anchor pier and should meet the required reserved length after cement pouring to facilitate on-site welding.

The specific features are as follows:
It shortens the construction period and reduces construction difficulty. The structural form of the sleeves welded at both ends of the ring forging allows for the welding process assessment of the anchor flange and corresponding pipeline, as well as the removal of welding slag, non-destructive testing of the welded joint, the water pressure test, and overall anti-corrosion work to be completed at the manufacturing plant. A certain length of straight pipe is left at both ends of the anchor flange for welding to the pipeline. This allows the anchor flange to be cast with the fixed pier at any time after transport to the construction site, without waiting for the pipeline to connect before pre-embedding, which greatly shortens the construction cycle and reduces difficulty.

Quality is easier to ensure. The sleeve-welded structure allows the welding of the anchor flange to be transferred to the manufacturing plant, avoiding the impact of harsh external environments on welding quality.

Eliminate the stress treatment of the coal joint to improve the reliability of the anchor flange. When welding the anchor flange, significant welding stress is generated at the joint. If not eliminated, it will affect the overall performance of the joint.
 

To meet the construction needs of the Sichuan-East Gas Transmission Pipeline Project, the anchor flange’s structural design was completed, the heat treatment temperature range for the ring forging was carefully selected, and the welding process for the ring forging and X70 pipeline steel was validated through welding process assessments. The new anchor flange products have been widely used in the Sichuan-East Gas Transmission Pipeline Project, yielding excellent results. The anchor flange uses a welding structure combining ring forging and sleeve. The welding of the ring forging and sleeve, welding process assessments, manufacturing, water pressure and bending tests, post-weld stress relief heat treatment, non-destructive testing, and anti-corrosion measures can all be completed at the manufacturing plant, ensuring both overall performance and corrosion resistance.
 
The flange ring forging has been precisely calculated and carefully designed. Its capacity to withstand internal pressure and axial bending moments meets the technical specifications for anchor flanges in the Sichuan-East Gas Transmission Pipeline Project. The flange ring forging is made from the same grade of materials as the main pipeline, offering good weldability and strength similar to the main pipeline. After the anchor flange is welded and formed, it undergoes stress relief annealing, further enhancing the product's performance.
 
The new structural anchor flange reduces on-site workload, minimizes the need for additional construction measures, and provides clear benefits. Based on different pipeline specifications, materials, working conditions, and other factors, the chemical composition of the anchor flange's raw materials can be tailored to match the corresponding pipeline, and through a refined manufacturing process, an anchor component that meets the project's needs can be produced. The anti-corrosion treatment of the anchor component is performed by skilled technicians in the factory, ensuring high-quality corrosion resistance. A total of 149 new anchor flanges were used throughout the Sichuan-East Gas Transmission Pipeline Project, and their performance has been satisfactory. The anchor flange design surpasses previous concepts, offering more reliable and simplified pipeline components for long-distance pipelines, particularly gas pipelines. It ensures high-quality on-site welding, improves work efficiency, and enhances overall project quality control. This structural anchor flange has significant potential for use in long-distance pipelines and is certain to provide stronger guarantees for project quality and progress.