This is a good engineering observation! Oil pipelines typically operate at much higher pressures than water pipelines. This is primarily due to differences in the physical properties of the fluids (especially viscosity) and the resulting economics, rather than any inherent differences in the "properties" of high pressure. Here's a detailed explanation:

1.  Core Difference: Fluid Viscosity

Water: Its viscosity is very low (about 1 centipoise at room temperature). This low viscosity means that water creates little internal frictional resistance when flowing through pipes.

Oil (especially crude oil): Its viscosity is much higher than that of water (ranging from a few centipoise to several thousand centipoise at room temperature, with heavy crude oil being particularly high). This high viscosity means that oil creates significant internal frictional resistance when flowing.

2.  The impact of viscosity on pipeline transportation: overcoming friction losses

Fluids flowing through pipes must overcome two main resistances:

Frictional resistance: Friction between fluid molecules and between the fluid and the pipe wall.

Altitude resistance: The energy required to lift the fluid to a higher altitude.

For long-distance pipelines, frictional resistance is often the dominant factor.

Water (low viscosity): Due to its low viscosity, water generates a relatively small frictional pressure drop when flowing through a pipe at the same flow rate and pipe diameter. Therefore, high pumping pressures are not required to maintain the required flow rate and flow rate. Lower pressures (typically in the range of several MPa to over ten MPa) are usually sufficient.

Oil (high viscosity): High viscosity results in a significant frictional pressure drop. If pressure is insufficient, oil flow can become very slow or even stagnate (especially at low temperatures or when transporting heavy oils). To maintain the necessary flow rate and flow rate, very high pressures (typically several MPa to over ten MPa or even higher, with mains pressures of 4-10 MPa or more common) must be applied to overcome the significant frictional resistance. High pressure is necessary to push viscous oil products to flow over long distances.

3.  Economic considerations: pipe diameter and pumping station

Ways to Reduce Friction Losses: There are two main approaches:

Increasing Pipe Diameter: A larger pipe diameter significantly reduces flow velocity, thereby significantly reducing friction losses (friction losses are roughly proportional to the square of the flow velocity).

Increasing Pressure: This provides a greater driving force (pressure differential) to overcome friction losses.

Choosing Water Pipelines: Water has low viscosity, so friction losses are inherently low. Even for long-distance transportation, increasing pipe diameter is generally a cost-effective option. While large-diameter water pipes have higher initial construction costs, they require lower operating pressures, resulting in lower energy consumption and maintenance costs for pumping stations. Low-pressure operation is also safer and requires less material. Therefore, a common strategy is "low-pressure, large-diameter pipes."

Choosing Oil Pipelines: Oil has high viscosity, resulting in significant friction losses. Reducing losses solely by increasing pipe diameter would require a very large pipe diameter, resulting in:

A sharp increase in pipeline material costs (steel).

Construction difficulty and costs (welding, laying, and corrosion protection) increase dramatically.

Occupies more space.

For long-distance, transnational/intercontinental pipelines, this is unacceptable.

Solution - High Pressure: Oil pipelines tend to utilize higher pressures combined with relatively smaller pipe diameters:

Small pipe diameters reduce material and construction costs.

High pressure provides sufficient driving force to overcome the significant friction caused by high viscosity.

While high pressure requires thicker pipe walls (increasing material costs), more powerful pumps, and stricter sealing/safety measures, on balance, for long-distance transportation of high-viscosity fluids, a "high-pressure, small-diameter" solution is generally more economical than a "low-pressure, extra-large-diameter" solution. The investment and operating costs of high-pressure pumping stations are offset by significant savings in pipe and construction costs.

4.  Density differences (minor factor)

Water's density (~1000 kg/m³) is typically higher than that of crude oil (~800-900 kg/m³) and refined petroleum products.

When overcoming elevation changes (such as crossing mountains and valleys), the higher the density, the higher the static head required to lift the fluid. This means that for the same amount of elevation lift, a water pipeline must overcome a greater static head than an oil pipeline. This is indeed a disadvantage for water pipelines.

However, in long-distance pipelines, frictional losses are often far greater than elevation losses. The significant frictional losses caused by high viscosity are the primary driving force behind the high pressures required for oil pipelines, with the impact of density differences being relatively minor.

5.  Other factors

Transportation Purpose: Municipal water supply typically has a maximum pressure limit (to prevent pipe bursts and ensure appropriate water pressure at the user end), while industrial oil transportation focuses primarily on efficient transportation.

Leakage Risk: High-pressure oil pipelines pose extremely high environmental and fire risks, but this does not prevent their use, as economic efficiency is the primary consideration. The risk of leaks in high-pressure water pipelines is relatively low (primarily flooding losses).

Fluid Compressibility: Although both oil and water have low compressibility, at extremely high pressures, this slight compressibility may have a subtle impact on system design (such as water hammer protection), but it is not the primary factor in determining pressure selection.

Heating to Reduce Viscosity: Some high-viscosity crude oil pipelines use heating to reduce viscosity, allowing operation at relatively low pressures. However, this requires additional heating stations and insulation measures, resulting in high energy consumption and costs. For most long-distance pipelines, high-pressure cold transportation remains the mainstream.

Summary:

The core reason for high-pressure operation in oil pipelines (compared to water pipelines) is the high viscosity of oil. High viscosity creates significant frictional resistance, necessitating high pressure to drive the fluid and achieve the required flow rate. A "high-pressure, small-diameter" approach is more economically viable than a "low-pressure, large-diameter" approach designed to minimize frictional losses.

For water pipelines, due to the low viscosity and low frictional losses, a "low-pressure, large-diameter" approach can generally meet transportation requirements and offers advantages in terms of overall cost (construction and operation), safety, and end-use requirements. Density differences (water is heavier, oil is lighter) can slightly hinder water pipelines when overcoming elevation changes, but this is far less significant than the impact of viscosity differences.

Therefore, high pressure isn't an inherent "property" of oil or water pipelines; rather, it's a design choice engineers make to achieve their delivery goals based on the fluid's physical properties (primarily viscosity) and economic efficiency.

For leaks in high-pressure water pipelines, high-pressure pipe repair clamps can be used.

For leaks in high-pressure oil pipelines, high-pressure pipe repair clamps can be used.