The Difference Between SCH 40 and SCH 40S

Introduction

In pipeline systems for petrochemicals, water supply, food processing, and pharmaceuticals, we frequently encounter pipe schedule such as SCH40 and SCH40S.For those unfamiliar with them, SCH40 and SCH40S are very easy to confuse because they look nearly identical, differing only in the addition of an “S” after the “40.” SCH40S is considered superior to SCH40.Through this article, let’s explore the differences between SCH40 and SCH40S, providing you with a practical guide for selecting the appropriate pipe schedule.

What is SCH (Schedule)

In the pipe schedule, SCH refers to the pipe wall thickness schedule, an international measurement standard established by the American Society of Mechanical Engineers (ASME).Understanding SCH enables us to better grasp the pipe schedule of SCH40 and SCH40S.Common SCH grades include SCH10, SCH20, SCH40, and SCH80. The number following the pipe schedule corresponds to the pipe wall thickness. A higher number indicates a thicker pipe wall, resulting in greater strength and pressure resistance.Conversely, the smaller the number, the thinner the pipe wall, resulting in lower strength and pressure resistance. During construction, the number following SCH indicates the steel pipe’s wall thickness, strength, pressure resistance, weight, and suitable environment, enabling us to select appropriate pipes, improve construction efficiency, and reduce maintenance costs. For example:

Standard Dimensions and Weight Chart for SCH40 and SCH40S Steel Pipes

In SCH40S, the “S” following 40 denotes “Stainless,” describing the material composition of the steel pipe.

The difference between SCH40 and SCH40S is that SCH40 is made of carbon steel or other materials, while SCH40S is made of stainless steel.Due to the differing materials of SCH40 and SCH40S, SCH40 and SCH40S steel pipes exhibit variations in application scope, pressure resistance, service life, and corrosion resistance. Compared to other materials such as stainless steel, carbon steel, and PVC, SCH40 and SCH40S demonstrate superior performance, offering higher strength and enhanced corrosion resistance.

Standard Dimensions and Weight Chart for SCH40 and SCH40S Steel Pipes

Differences Between SCH 40 and SCH 40S

Corrosion Resistance

Compared to SCH40, SCH40S pipes offer superior corrosion resistance. SCH40S is constructed from stainless steel, where chromium reacts with oxygen to form a protective chromium oxide film that effectively prevents oxidation and corrosion. Even in highly corrosive marine or chemical environments, SCH40S maintains excellent performance and resists degradation. SCH40 pipes are made from materials like carbon steel, suitable for dry environments. Carbon steel may corrode in harsh conditions, necessitating galvanization for corrosion protection. However, the galvanized coating gradually thins or peels over time, diminishing its protective effectiveness.

Pressure Resistance

Although SCH 40 has thicker walls than SCH 40S, SCH 40S offers superior high-pressure resistance and can withstand greater pressure. This is primarily due to SCH 40S being made of stainless steel. Stainless steel differs from carbon steel in alloy composition, microstructure, and manufacturing processes, resulting in higher strength and pressure resistance. Additionally, SCH 40 has a smaller inner diameter than SCH 40S, limiting its ability to withstand higher pressures.

Service Life

The service life of pipes varies depending on factors like corrosion and wear. In humid or highly corrosive environments, SCH 40 is susceptible to corrosion, which shortens its lifespan. SCH 40 pipes can be improved through galvanized coating, reducing corrosion risk and extending service life. Galvanized SCH 40 steel pipes can last 40-70 years. However, the galvanized coating will eventually wear off over time. Regular inspections of the pipes are necessary, requiring re-galvanization or replacement of severely corroded pipes. Compared to SCH 40, SCH 40S is more durable, with a service life extending up to 80 years.

Installation and Maintenance

Due to differences in material composition, SCH 40 pipes are lighter than SCH 40S pipes, making them easier to transport and install. SCH 40S pipes require higher welding skills and more experienced workers for installation, resulting in higher welding costs. However, because SCH 40S pipes offer superior corrosion resistance, higher pressure tolerance, and a longer service life, they ultimately lead to lower maintenance costs over time.

Purchase Price

Due to the superior material quality of SCH 40S, its purchase price is higher compared to SCH 40, which offers a more economical option. You can select the appropriate pipe schedule based on your specific application to reduce the cost of purchasing or maintaining steel pipes.

Application Areas

SCH 40 complies with standards such as ASTM A53 and ASTM A106, while SCH 40S adheres to standards like ASTM A312 and ASTM A213. SCH 40 is suitable for low-to-medium pressure and temperature environments, such as water supply, gas distribution, and agricultural irrigation. SCH 40S is suitable for highly corrosive, high-hygiene-requirement, high-temperature, and high-pressure environments, such as food processing, oil and gas transportation, and pharmaceutical manufacturing.

Summary

SCH40 and SCH40S differ in corrosion resistance, pressure rating, service life, ease of installation, and application areas. In highly corrosive, high-temperature, and high-pressure environments, SCH 40S is the more suitable choice due to its extended service life and durability. For medium-to-low pressure and temperature conditions, SCH 40 offers better cost-effectiveness and is suitable for general industrial applications. Understanding the characteristics of SCH40 and SCH40S enables you to select the most appropriate pipe schedule for your needs.