1. Consider the pressure of the conveying medium

For oil and gas pipelines, pressure is a key factor. If the conveying pressure is low, such as in urban gas distribution networks, the pressure is generally less than 0.4 MPa. For smaller pipe diameters (such as DN100-DN300), thin-walled LSAW Steel Pipes with a wall thickness of less than 8mm can be selected. Because in this low-pressure environment, thinner pipe walls can withstand internal pressure while reducing costs and construction difficulty.

For high-pressure long-distance oil and gas pipelines, such as onshore long-distance trunk lines with a transmission pressure of 4-10MPa and larger pipe diameters (such as DN800-DN1400), thick walled LSAW steel pipes are required. For example, steel pipes with a wall thickness of 16-22mm and higher steel strength grades (such as X70, X80) may be selected to ensure that the pipeline can withstand enormous internal pressure without rupture.

2. Consider the properties of the conveying medium

When the medium being transported is corrosive, such as acidic natural gas containing hydrogen sulfide or oil-water mixtures with high salt content, it is necessary to increase the wall thickness appropriately. Because corrosion weakens the wall thickness of steel pipes and reduces their load-bearing capacity. For this situation, in addition to considering the use of anti-corrosion coatings, steel pipes slightly thicker than normal should also be selected. For example, in pipelines transporting acidic natural gas, if the normal wall thickness is 10mm, considering corrosion factors, the wall thickness may be increased to 12-14mm.

For media with high viscosity or containing solid particles, such as heavy oil or sand containing crude oil, the wear and erosion inside the pipeline are more severe. This requires thicker pipe walls to resist wear and prevent the pipe walls from being worn through. At the same time, in order to ensure the normal transportation of the pipeline, higher transportation pressure may be required, which further requires an increase in wall thickness.

3. Consider the laying environment of the pipeline

Underground laying: If the pipeline is laid underground, factors such as soil type, groundwater level, and soil corrosiveness need to be considered. In soft soil foundation, pipelines may be subjected to significant soil pressure and require sufficient wall thickness to resist deformation. For example, in soft soil geological conditions in coastal areas, for pipelines with diameters ranging from DN600 to DN1000, the wall thickness may need to be increased by 2-4mm compared to normal conditions. If the groundwater level is high and the soil is corrosive, anti-corrosion measures should be considered and the wall thickness should be appropriately increased to extend the service life of the pipeline.

Underwater laying (such as submarine pipelines): For pipelines laid underwater, external pressure generated by water depth should be considered. In shallow waters, for every 10 meters increase in water depth, there will be an increase of approximately 0.1 MPa in external pressure. For example, when laying pipelines in waters with a depth of 100-500 meters, in addition to withstanding internal oil and gas pressure, it is also necessary to withstand the enormous pressure of seawater, which may require extra thick LSAW steel pipes with a wall thickness of 18-25mm, and anti-corrosion and anti erosion measures should be taken.

Ground laying (such as crossing valleys, etc.): Pipelines laid on the ground, such as pipeline bridges crossing valleys or rivers, need to consider factors such as wind load, snow load, and thermal stress caused by temperature changes. In high-altitude regions, temperature changes are large, and the thermal expansion and contraction of pipelines will generate significant stress. To resist these external loads and stresses, it is necessary to choose steel pipes with appropriate wall thickness. For example, in high-altitude and high-altitude areas, pipelines crossing valleys may require a wall thickness of 10-16mm for pipes with diameters ranging from DN400 to DN800, and expansion compensation devices may also need to be installed.

4. Consider the service life and maintenance requirements of the pipeline

If the project requires pipelines to have a longer service life, such as 30-50 years, it is necessary to choose steel pipes with slightly thicker walls to cope with various losses during long-term use. For example, for pipelines that transport high-temperature crude oil for a long time, thicker wall thickness can delay pipeline aging and damage due to thermal stress and the corrosive effect of crude oil.

From a maintenance perspective, in some difficult to maintain locations such as pipelines in deep sea or remote mountainous areas, it is advisable to choose steel pipes with sufficient wall thickness to reduce the possibility of repairs. Because the maintenance cost and difficulty of these locations are high, sufficient wall thickness can reduce the risk of pipeline failure.

5. Consider the economic cost of the project

On the premise of meeting safety and functional requirements, the cost of steel pipes should be comprehensively considered. Thin walled steel pipes have relatively low prices, but if frequent maintenance or replacement is required due to insufficient wall thickness, long-term costs may increase. Although thick walled steel pipes have a high one-time investment cost, they can reduce the frequency of maintenance and replacement under high pressure, harsh environments, and other conditions, thereby lowering long-term operating costs. For example, in the internal gathering and transportation system of a large oil and gas field, for pipeline sections with lower transmission pressure and relatively better environment, thinner steel pipes can be selected to reduce initial investment; For key long-distance trunk lines or export pipelines, even if the cost is high, thick walled steel pipes should be selected to ensure safe and long-term stable operation.

Experience and skills in selecting LSAW steel pipe wall thickness

1. Gain a deep understanding of engineering requirements

Clarify the characteristics of the conveying medium: If conveying highly corrosive media (such as natural gas containing hydrogen sulfide), in addition to considering anti-corrosion measures, the wall thickness should be appropriately increased. For example, the wall thickness of a pipeline transporting ordinary natural gas is 10mm, while for pipelines containing hydrogen sulfide natural gas, the wall thickness may need to be increased to 12-14mm. At the same time, the temperature and viscosity of the medium should be considered. High temperature media can cause thermal stress in steel pipes, which may require increasing wall thickness to resist deformation; High viscosity media may experience significant pressure drop during transportation, requiring higher transportation pressure and increasing wall thickness.

Determine the range of conveying pressure: For pipelines with high-pressure conveying (such as conveying pressure greater than 4MPa), a thicker wall thickness is required to withstand internal pressure. Generally speaking, for every 1 MPa increase in conveying pressure, depending on the pipe diameter and strength grade, the wall thickness may need to be increased by 2-5mm. For example, in a pipeline with a diameter of DN800, increasing the conveying pressure from 2MPa to 6MPa may require an increase in wall thickness from 10mm to 18-20mm.

Consider the pipeline laying environment:

Underground laying: If the soil is highly corrosive or the groundwater level is high, anti-corrosion measures and increasing wall thickness need to be considered. For example, in soft soil geology in coastal areas, for pipelines with diameters ranging from DN600 to DN1000, the wall thickness may increase by 2-4mm compared to normal conditions. At the same time, the bearing capacity of the soil should be considered. In soft soil foundations, pipelines may be subjected to significant soil pressure and require sufficient wall thickness to resist deformation.

Underwater laying (such as submarine pipelines): Water depth is a key factor, and for every 10 meters increase in water depth, an external pressure of approximately 0.1 MPa will be added. For example, when laying pipelines in waters with a depth of 100-500 meters, in addition to withstanding internal oil and gas pressure, it is also necessary to withstand the enormous pressure of seawater, which may require extra thick LSAW steel pipes with a wall thickness of 18-25mm, and anti-corrosion and anti erosion measures should be taken.

Ground laying (such as crossing valleys): Factors such as wind load, snow load, and thermal stress caused by temperature changes need to be considered. In high-altitude regions, temperature changes are large, and the thermal expansion and contraction of pipelines will generate significant stress. For pipelines with diameters ranging from DN400 to DN800, the wall thickness may need to be between 10-16mm, and expansion compensation devices may also be required.

2. Refer to relevant standards and specifications

International standards, such as API SPEC 5L (American Petroleum Institute standard), specify the dimensions, steel grades, performance, and other aspects of steel pipes used in the transportation of oil and gas industries. It specifies the mechanical performance requirements for different grades of steel pipes, and wall thickness is one of the important factors affecting the mechanical performance of steel pipes to meet the standards. For example, according to this standard, there are clear requirements for the allowable deviation of the outer diameter and other dimensional parameters of steel pipes within a certain range of outer diameter and wall thickness, which can help determine a reasonable range of wall thickness.

National and industry standards: China's GB/T 9711 (equivalent to ISO 3183) specifies the technical requirements for steel pipes for transportation in the petroleum and natural gas industry, including allowable deviations in wall thickness. The construction industry standards such as JGJ 81-2011 (Technical Specification for Welding of Steel Structures in Buildings) have different regulations on the selection of welding process parameters and the design of welding joint forms for steel pipes with different wall thicknesses when it comes to the welding of LSAW steel pipes. These regulations also affect the selection of wall thickness, as welding quality is closely related to the wall thickness of steel pipes.

3. Conduct detailed engineering calculations and simulations

Strength calculation: Based on internal pressure, external pressure, axial force and other loads, use theoretical formulas (such as Latin American formula, external pressure cylinder stability formula, etc.) to calculate the minimum wall thickness required. For example, for pipelines subjected to internal pressure, \ (t=\ frac {PD} {2 [\ sigma]} \) (thin-walled cylinder) or \ (t=\ frac {D} {2} \ left (1- \ sqrt {\ frac {[\ sigma] - P} {[\ sigma]+P} \ right) \) (thick walled cylinder) can be used for calculation. For pipelines under external pressure, \ (P_ {cr}=\ frac {2E} {1- \ nu ^ {2}} \ left (\ frac {t} {D} \ right) ^ {3} \) (long cylinder) or \ (P_ {cr}=\ frac {2.59Et ^ {2} {LD \ sqrt {1- \ nu ^ {2}} \) (short cylinder) is used to consider the stability of the pipeline and determine the wall thickness.

Finite element simulation: Using finite element analysis software, simulate the stress-strain state of pipelines under complex working conditions (such as combined loads, complex terrain, etc.). Through simulation, it is possible to more accurately understand the weak links of the pipeline and optimize the selection of wall thickness. For example, in pipeline engineering crossing valleys, finite element simulation can consider the comprehensive effects of various factors such as wind load, pipeline self weight, thermal stress, etc., to determine the stress distribution at different positions of the pipeline and provide a basis for local adjustment of wall thickness.

4. Consider economic costs and maintainability

Economic cost balance: Thin walled steel pipes have relatively low prices, but if frequent maintenance or replacement is required due to insufficient wall thickness, long-term costs may increase. Although thick walled steel pipes have a high one-time investment cost, they can reduce the frequency of maintenance and replacement under high pressure, harsh environments, and other conditions, thereby lowering long-term operating costs. For example, in the internal gathering and transportation system of a large oil and gas field, for pipeline sections with lower transmission pressure and relatively better environment, thinner steel pipes can be selected to reduce initial investment; For key long-distance trunk lines or export pipelines, even if the cost is high, thick walled steel pipes should be selected to ensure safe and long-term stable operation.

Maintainability factor: In some difficult to maintain locations, such as pipelines in deep sea or remote mountainous areas, it is advisable to choose steel pipes with sufficient wall thickness to reduce the possibility of repairs. Because the maintenance cost and difficulty of these locations are high, sufficient wall thickness can reduce the risk of pipeline failure. At the same time, it is necessary to consider whether the selected wall thickness is convenient for on-site construction and installation, for example, excessively thick steel pipes may increase welding difficulty and construction period.