In the field of oil pipeline construction, there are significant differences between offshore and onshore environments, which have a multi-faceted impact on steel pipe costs. The following compares the steel pipe costs of the two from multiple key factors.

I. Material requirements and cost differences

(I) Offshore pipeline steel pipe material

The offshore environment is complex, seawater is highly corrosive, and pipelines need to withstand huge water pressure. Taking the "Nord Stream Pipeline" as an example, it is made of high-tensile steel with a yield strength of 450 MPa, far exceeding ordinary steel, and the pipeline thickness can reach 41 mm. The research and development and production process of this high-performance steel is complex and costly. In addition, in order to resist seawater corrosion, the steel pipe needs to be coated with a special anti-corrosion coating on the outside and an anti-friction coating on the inside. For example, the outer coating of the "Nord Stream Pipeline" can resist seawater corrosion, and the inside is composed of a two-component epoxy resin flow coating, which reduces friction and limits pressure drop, ensuring better flow of natural gas and reducing compression costs. The material and construction costs of these coatings further increase the overall cost of offshore pipeline steel pipes.

(II) Material of steel pipes for onshore pipelines

Although onshore pipelines do not need to withstand seawater corrosion and huge water pressure, factors such as soil corrosion and temperature changes must be considered. Generally, pipeline steel that meets the corresponding standards is selected, such as X60, X70, X80 and other steel grades. Compared with steel used for offshore pipelines, onshore pipeline steel has relatively lower requirements for strength and corrosion resistance (of course, high-grade steel may also be used under some special geological and environmental conditions). For example, in ordinary soil environments, X70 steel grade steel pipes are widely used, and their prices are lower than high-tensile steel used for offshore pipelines. At the same time, the requirements for onshore pipeline anti-corrosion coatings are relatively simple, and common ones include three-layer polyethylene (3PE) anti-corrosion coatings, fused epoxy powder (FBE) anti-corrosion coatings, etc., and the cost is also lower than the special coatings for offshore pipelines.

II. Relationship between manufacturing process and cost

(I) Manufacturing of offshore pipeline steel pipes

The manufacturing precision and quality requirements of offshore pipeline steel pipes are extremely high. Since the pipe sections need to be spliced ​​at sea, strict requirements are placed on welding performance, dimensional accuracy, etc. Advanced automated production equipment and testing technology are required during the manufacturing process to ensure that each section of steel pipe meets high standards. For example, in large offshore pipeline projects, steel pipe manufacturers need to invest a lot of money to purchase high-precision production equipment and establish a strict quality inspection system, which increases production costs. Moreover, offshore pipeline steel pipes often need to be customized with special specifications and performance, which further increases the difficulty and cost of manufacturing.

(II) Onshore pipeline steel pipe manufacturing

The onshore pipeline steel pipe manufacturing process is relatively mature and has a high degree of standardization. Most onshore steel pipes can be mass-produced on conventional production lines with high production efficiency and relatively low cost. Although there are also quality control processes, the inspection accuracy and special performance requirements are not as stringent as those of offshore pipeline steel pipes. For example, common specifications of onshore pipeline steel pipes can be mass-produced through automated production lines, which reduces the unit production cost. In the manufacturing process, onshore pipeline steel pipes have obvious cost advantages.

III. The impact of transportation and installation on steel pipe costs

(I) Transportation and installation of offshore pipeline steel pipes

Offshore transportation and installation of steel pipes face many challenges and are costly. First, special ships are needed to transport steel pipes, and the steel pipes must be ensured not to be damaged during transportation, which increases transportation costs. During installation, large pipe-laying vessels are required for operation. The rental cost of pipe-laying vessels is high, and the installation process is greatly affected by factors such as weather and sea conditions. The operation window period is limited, resulting in low installation efficiency and increased costs. For example, when laying offshore pipelines in deep sea areas, pipe-laying vessels need to have special positioning and laying technologies, which further increases the installation cost. Moreover, offshore installation has high technical requirements for construction personnel, and labor costs also increase accordingly.

(II) Transportation and installation of steel pipes for onshore pipelines

Land transportation is relatively convenient and can be carried out by conventional transportation methods such as roads and railways, with relatively low transportation costs. During installation, although professional construction equipment is also required, the equipment requirements and construction difficulty are lower than those at sea. For example, conventional equipment such as excavators and pipe loaders can be used for onshore pipeline installation. The construction is less restricted by natural conditions, the construction efficiency is higher, and the installation cost is much lower than that at sea. In the transportation and installation links, the cost advantage of onshore pipeline steel pipes is outstanding.