What Is Steel Pipe Dimensions Schedule?

What Is Steel Pipe Dimensions Schedule?

Steel pipe schedule is an indicating method represented by ASME B 36.10, and used in many other standards, marked with “Sch”. Sch is the abbreviation of schedule, generally appearing in the American steel pipe standard, which is a prefix of a series number. For example, Sch 80, where “80” is a pipe number from chart/table ASME B 36.10.

“Since the steel pipe’s main application is to transport the fluids under pressure, their internal diameter is their critical size. This critical size is taken as nominal bore (NB). Therefore, if steel pipe carries the fluids with pressure, it is particularly important that pipe shall have enough strength and wall thickness. So wall thickness is specified in Schedules, which means the pipe schedule, abbreviated as SCH. Here ASME is the given standard and definition for the pipe schedule.”

The Meaning of Steel Pipe Schedule

A steel pipe schedule represents the wall thickness of the pipe. It is indicated by numbers such as SCH 40, SCH 80, and SCH 160. These numbers correspond to specific dimensions, which include the inner and outer diameter as well as the wall thickness. Knowing these values ensures compatibility with equipment and adherence to standards.

When describing the steel pipe parameter, we usually use the pipe schedule, which is a method that represents pipe wall thickness with number. Pipe schedule (sch. ) is not a wall thickness, but a wall thickness series. Different pipe schedules mean different wall thicknesses for the steel pipe in the same diameter. The most frequent indications of schedule are SCH 5, 5S, 10, 10S, 20, 20S, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160. The larger the table number, the thicker the surface pipe wall, the higher the pressure resistance.

Schedule 40, 80 steel pipe dimension means

If you are new to the pipe industry, you may wonder why you always see schedule 40 or 80 steel pipes everywhere. What kind of material is used for these pipes?

As you have read above articles you know that Schedule 40 and 80 represent pipe wall thickness, but why are they always searched by buyers?

Here is the reason:

Schedule 40 and 80 steel pipes are commonly required in various industries due to the typical pressure they can withstand. Because these pipes are designed to handle higher pressures, they are often requested in large quantities to meet the demands of different industries.

The material standard for such thickness pipes has no limitations, you could ask for sch 40 stainless steel pipe, like ASTM A312 Grade 316L; Or sch 40 carbon steel pipe, such as API 5L, ASTM A53, ASTM A106B, A 179, A252, A333 etc..

What is the Nominal Pipe Size (NPS)?

Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. Pipe size is specified with two non-dimensional numbers: a nominal pipe size (NPS) based on inches, and a schedule (Sched. or Sch.).

How Pipe Schedule Is Determined

The schedule number is calculated based on the wall thickness and the pipe's nominal size. The formula connects these values to define the pressure-carrying capacity of the pipe. Higher schedules like SCH 80 or SCH 160 indicate thicker walls, making the pipes suitable for high-pressure applications.

What is DN (Nominal Diameter)

Nominal diameter, also known as outside diameter, is used to represent the general diameter of various pipes and pipeline accessories. Due to the thin wall of the pipe, the outside and inside diameters are almost the same. Therefore, the average value of both parameters is used as the nominal diameter of the pipe. DN (nominal diameter) ensures that pipes and pipe fittings with the same nominal diameter can be interconnected, providing interchangeability. Although the nominal diameter value is close to or equal to the inside diameter of the pipe, it does not represent the actual sense of the pipe diameter. The nominal size is denoted by a numerical symbol followed by the letter “DN” and the unit is indicated in millimeters after the symbol. For example, DN50 represents a pipe with a nominal diameter of 50 mm.

DN (mm) and NPS (inch) conversion

Nominal diameter DN (mm) and NPS (inch) conversion

Why Pipe Schedule Is Important

Pipe schedules directly impact the pipe's performance. Industries such as oil and gas, construction, and manufacturing rely on pipes that meet precise specifications. The correct pipe schedule ensures proper flow, prevents leakage, and withstands the required pressure levels.

Common Steel Pipe Schedule Types

Schedule 10: Light-duty applications like low-pressure systems or non-critical processes.

Schedule 40: Widely used in plumbing, construction, and general piping.

Schedule 80: Suited for high-pressure environments, offering enhanced strength.

Schedule 160: Used in extremely high-pressure systems, such as industrial or chemical processes.

Pipe Weight Class Schedule

The WGT class (weight class) is an indication of the pipe wall thickness that was used in the past, but is still in use today. It consists of three grades: STD (standard), XS (extra strong), and XXS (double extra strong).

In the early days of pipe production, each size of pipe had only one specification, known as standard tube (STD). However, in order to handle high pressure fluids, thicker pipes known as XS were introduced. XXS pipes were then developed to handle even higher pressure fluids. As new materials processing technology emerged, there was a growing demand for more cost-effective thin-walled pipes. This eventually led to the introduction of the aforementioned pipe grades. The corresponding relationship between pipe schedules and weight classes can be found in the ASME B36.10 and ASME B36.19 specifications.

Key Differences Between Schedules

The main difference lies in the wall thickness. For instance, a Schedule 40 pipe has thinner walls compared to Schedule 80. This difference affects the pipe's weight, durability, and ability to handle internal pressure. Heavier schedules offer greater strength but are costlier and harder to handle.

How to describe steel pipe dimensions and size correctly?

For example: a. Expressed as “pipe outside diameter × wall thickness”, such as Φ 88.9mm x 5.49mm (3 1/2” x 0.216” ).  114.3mm x 6.02mm (4 1/2” x 0.237”), length 6m (20ft) or 12m (40ft), Single Random Length (SRL 18-25ft), or Double Random Length (DRL 38-40ft).

b. Expressed as “NPS x Schedule”, NPS 3 inch x Sch 40, NPS 4 inch x Sch 40. Same size as above specification.

c. Expressed as “NPS x WGT Class”, NPS 3 inch x SCH STD, NPS 4 inch x SCH STD. Same size above.

d. “Pipe Outer Diameter x lb/ft.” is commonly used in North America and South America. For example, a pipe with an outer diameter of 3 1/2” would be described as having a weight of 16.8 lb/ft. The unit “lb/ft” stands for pounds per foot.

Applications of Steel Pipe Schedules

Steel pipes with specific schedules find use in diverse industries:

Oil and Gas: High-pressure pipelines for transporting crude oil and natural gas.

Construction: Structural applications where strength and durability are crucial.

Plumbing: Water supply and drainage systems.

Chemical Processing: Transporting corrosive materials under high pressure.

Selecting the correct schedule ensures the pipe can endure the operating conditions without failure.

Conclusion

Understanding steel pipe dimensions schedule is vital for choosing the right pipe for a project. This system standardizes the dimensions and ensures compatibility across applications. Whether used in low-pressure plumbing or high-pressure industrial settings, knowing the correct schedule prevents costly errors and enhances operational efficiency. Proper selection leads to safer, longer-lasting, and more effective piping systems.

By considering the specifications, thickness, and intended use, you can make informed decisions that optimize both performance and cost.