Performance of Large-diameter Welded Pipes for Water Delivery

Jan 10, 2023

A spiral welded pipe is the most used water delivery steel pipe. It is made of hot-rolled steel coils after spiral cold processing, and then automatically welded by the inner and outer double-sided submerged arc. The specific production process is shown in figure 1.

1.1 Strength
The steel pipe for water delivery has high strength, which can ensure the safety and reliability of the water delivery. With the advancement of metallurgical technology, advanced TMCP and microalloying technologies are used in the manufacture of pipeline steel plates, which ensures the stability of structure and performance of the pipe, and greatly improves the mechanical properties of the pipe. The burst pressure is higher than 3 times the design working pressure, ensuring the safe operation of the pipeline. The strength of the water delivery steel pipe is 350 to 800MPa, and the distribution is shown in Figure 1. It has different strengths and can be selected according to the user’s needs. The pipe with higher strength can increase the delivery pressure of the water delivery steel pipe, improve the safety, and at the same time, reduce the wall thickness of the pipe and investment.

Figure 1 Strength of water delivery steel pipes

1.2 Toughness
Water delivery steel pipes have good ductility and plasticity, excellent deformation resistance, and are especially suitable for deformation zones. Figure 2 shows the tensile curve of conventional carbon steel water delivery pipes. It can be seen from Figure 2 that, compared with other water delivery pipes, the water delivery steel pipe has a higher deformation strengthening index n, better uniform deformation ability, and can withstand instantaneous pressure of the water pipeline, meeting the requirement of the stress and strain for water hammer, earthquake, landslide, vehicle vibration and foundation instability, ensuring that it will deform without failure under extreme conditions and reducing the risk of pipelines.

Figure 2

1.3 Dimensional accuracy
The size and shape of the water delivery steel pipe are controlled with high precision, which is convenient for on-site construction; the length of the pipe can be controlled flexibly. The weight is light, and the project cost can be saved. At present, the welded steel pipe adopts advanced forming and welding technology to ensure that the pipe body has good geometric size and good welding. The end of the steel pipe is cold-expanded to ensure that the diameter (circumference) and roundness of the pipe end has good accuracy, which is easy to install on the construction site. The pipe length can be customized according to the project site and user requirements, minimizing the number of pipeline joints and reducing potential safety hazards. Compared with PCCP pipes and ductile iron pipes with the same wall thickness and quality, steel pipes are significantly lighter. The wall thickness and weight of steel pipes with different specifications are shown in Figure 3. The use of water delivery steel pipes can reduce additional engineering costs such as hoisting and transportation, reducing engineering costs.

Figure 3

1.4 Pipe ends
The pipe end of the water delivery steel pipes is connected by welding, which has a good bonding force and can meet complex geological environments. The end adopts metallurgical bonding, which has high strength, good corrosion resistance and good adaptability. Pipelines can be laid under harsh conditions such as high pressure, overhead, swamps, and rivers. The excavation area is small during the road construction process, which requires less foundation. Welding on the trench can also be used to improve construction efficiency and reduce construction costs. In addition, welding can be used to repair leaks, which saves time, does not need to dig the entire pipeline, and can quickly restore the pipeline's operational capacity.

1.5 The capacity of the pipe
The raw materials, auxiliary materials and product supply capabilities are good, which can ensure the smooth construction of pipelines. Raw materials come from domestic iron and steel enterprises (Baowu Steel, Anshan Iron and Steel, Shougang, Taiyuan Iron and Steel, Maanshan Iron and Steel, etc.), and product quality and supply capacity is guaranteed. Taking Baoji Steel Pipe as an example, the company has 13 large-diameter submerged arc welded pipe production lines with an annual production capacity of 1.5 million tons, which can effectively guarantee the progress of the project.

1.6 Testing pipes
The on-line quality control of large-diameter welded steel pipes is very strict in the production process, mainly including 100% welding seam X-ray inspection, 100% welding seam and pipe body ultrasonic automatic flaw detection, 100% welding seam manual ultrasonic inspection, 100% hydrostatic pressure tests, 100% X-ray filming of pipe end welding seams, 100% appearance, and size inspection, to ensure the quality of each steel pipe produced is reliable. Complete physical and chemical performance inspection of finished steel pipes from structure to performance, mainly including chemical analysis (direct reading spectrometers), tensile tests, guided bending tests, drop weight impact tests (DWTT), pendulum impact tests, hardness tests, metallographic analysis, band structure and inclusion analysis, grain size evaluation and macroscopic appearance inspection of welding seams. The comparison of comprehensive performance of several water pipes is shown in Table 1. It can be seen from Table 1 that the welded steel pipe has excellent comprehensive performance, high-cost performance, and long service life.

Table 1 A comparison of the comprehensive performance of several water pipes

Types	Pressure bearing capacity	Anti-deformation capacity	On-site construction	Transportation	Corrosion resistance	Time for dealing with failures	Service life
Welded steel pipes	Good	Good	Good welding and bonding	Convenient	Selection according to the conveying medium	1	Above 50 days
Ductile iron pipes	Average	Average	Socket ends	Not difficult	/	2 to 5 days	30
PCCP	Poor	Poor	Socket ends	Difficult	/	Around 15 days	Around 25 days

Figure 4 shows a comparison of the economy between several water delivery steel pipes and ductile iron pipes. Compared with other pipes, the economic advantages of water delivery steel pipes with a diameter of 700 mm or more are particularly obvious.