Describing Steel Pipe Dimensions & Sizes

Describing Steel Pipe Dimensions & Sizes (Schedule 40, 80 Pipe) Effectively

When it comes to discussing steel pipes, it's easy to get lost in the jargon and end up with the wrong size. Imagine trying to convey your precise needs to a seller, only to realize later that what you received doesn't fit the bill. That's a hassle no one wants to deal with.

So, let's clear up the confusion and talk about the right ways to express the dimensions of steel pipes.

Understanding Pipe Dimensions

Steel pipes have three key elements that define their dimensions: outer diameter (OD), wall thickness (WT), and length. The outer diameter is the measurement across the widest point of the pipe, the wall thickness refers to how thick the pipe's walls are, and the length is typically either 20 feet (6 meters) or 40 feet (12 meters).

Now, why does this matter? Well, knowing these dimensions allows us to calculate crucial factors like the pipe's weight, its pressure-bearing capacity, and even its cost per foot or meter. In short, getting the size right is essential for ensuring the pipe meets your needs.

Let's Break It Down

1. Dimension Standards: Both carbon and stainless steel pipes adhere to specific dimension standards outlined by organizations like ASME. For carbon steel pipes, ASME B36.10M lays down the standards, while for stainless steel pipes, it's B36.19M. These standards ensure uniformity and compatibility across the industry.

2. Pipe Size Schedule: Ever heard of Schedule 40 or Schedule 80 steel pipes? These terms refer to the thickness of the pipes' walls and are crucial for determining their strength and suitability for different applications. Schedule 40 pipes have thinner walls and are commonly used for residential and light commercial purposes, while Schedule 80 pipes have thicker walls, making them suitable for heavy-duty industrial applications.

3. Nominal Pipe Size (NPS) and Nominal Diameter (DN): The nominal pipe size is a standardized designation used to indicate the approximate inside diameter of the pipe. It's essential to understand this terminology when discussing pipe sizes, as it helps ensure consistency and clarity in communication.

Visualizing the Dimensions  Here's a handy chart to illustrate the dimensions of steel pipes:

This chart provides a snapshot of common pipe sizes, outer diameters, wall thicknesses, and lengths, making it easier to visualize and understand the dimensions.

Understanding Steel Pipe Dimension Standards

When it comes to describing steel pipes, there's a set of standards in place to ensure clarity and consistency. These standards, such as ASME B 36.10 and ASME B 36.19, provide guidelines for specifying pipe sizes, outer diameters (OD), and wall thicknesses.

ASME B 36.10M: The Standard for Steel Pipe Dimensions

ASME B 36.10M outlines the dimensions and sizes of steel pipes, whether seamless or welded, that are used in various temperature and pressure conditions. It distinguishes pipes from tubes, emphasizing their use in pipeline systems for fluid transmission like oil, gas, water, and slurry. Notably, for pipes with an outer diameter smaller than 12.75 inches (NPS 12, DN 300), the actual diameter exceeds the nominal pipe size (NPS) or nominal diameter (DN). However, for larger sizes, the outside diameter matches the nominal size.

ASME B 36.19M: Stainless Steel Pipe Dimensions

ASME B 36.19M focuses on stainless steel pipe dimensions, covering both seamless and welded types. The specifications largely mirror those of ASTM B36.10M, with some differences in certain size ranges. For instance, sizes ranging from NPS 14 to NPS 22 (DN 350-550) have schedule 10S, while NPS 12 falls under schedule 40S, and NPS 10 and 12 are classified as schedule 80S.

Expressing Pipe Dimensions

When communicating pipe dimensions, several methods are used:

1. Pipe Wall Thickness: Steel Pipe Schedule, such as schedule 40 steel pipe or schedule 80 pipe.
2. Pipe Diameters: Nominal Pipe Size (NPS) and Nominal Diameter (DN).
3. Pipe Weight Class: Given in terms of pounds per foot (LB/FT) or kilograms per meter (KG/M).

Understanding Steel Pipe Schedule

Steel pipe schedule is a vital indicator denoted by "Sch" in ASME B 36.10 and other standards. It's a prefix followed by a series number, such as Sch 80. The schedule signifies the wall thickness, crucial for withstanding fluid pressure. The formula for pipe schedule involves the designed pressure (P) and allowable stress of materials under the design temperature ([ó]t). The higher the schedule number, the thicker the pipe wall and the greater the pressure resistance.

Schedule 40, 80 Steel Pipe Dimensions

Schedule 40 and 80 steel pipes are ubiquitous in various industries due to their ability to handle higher pressures. The demand for these pipes stems from their design to withstand elevated pressures, making them essential across industries. Material standards for such pipes vary, ranging from stainless steel to carbon steel, depending on the application.

In conclusion, understanding steel pipe dimension standards is crucial for ensuring the right fit for diverse industrial needs. Whether it's specifying the pipe size, outer diameter, or wall thickness, adherence to standards like ASME B 36.10M and B 36.19M ensures consistency and reliability in the steel pipe industry.

Understanding Nominal Pipe Size (NPS) and Nominal Diameter (DN)

Nominal Pipe Size (NPS) serves as a standardized set of sizes for pipes used across North America, designed to withstand varying pressures and temperatures. It comprises two key elements: the nominal pipe size (NPS) denoted in inches, and a schedule (Sched. or Sch.) indicating the pipe's wall thickness.

What is DN (Nominal Diameter)?

Nominal Diameter (DN), also referred to as outside diameter, represents the general diameter of pipes and pipeline accessories. Due to the thin walls of pipes, the outside and inside diameters are nearly identical. Therefore, DN is derived as the average value of both parameters, ensuring interchangeability and compatibility among pipes and fittings of the same nominal diameter. DN is indicated by a numerical symbol followed by "DN," with measurements in millimeters. For instance, DN50 corresponds to a pipe with a nominal diameter of 50 mm.

DN (mm) and NPS (inch) Conversion

Converting between Nominal Diameter (DN) in millimeters and Nominal Pipe Size (NPS) in inches involves several methods:

1. For DN sizes less than 100 mm, conversion requires individual memory:

   DN (mm)	NPS (inch)
   6	1/8
   8	1/4
   10	3/8
   15	1/2
   20	3/4
   25	1
   32	1 1/4
   40	1 1/2
   50	2
   65	2 1/2
   80	3

2. For DN sizes equal to or greater than 100 mm, the conversion formula is:

   DN = 25 * NPS; NPS = DN / 25

3. Exact conversion factor:

   1 inch = 25.4 mm

Pipe Weight Class Schedule

The Weight Class (WGT) schedule indicates the wall thickness of pipes, comprising three grades: Standard (STD), Extra Strong (XS), and Double Extra Strong (XXS). Initially, pipes were categorized into Standard (STD) only. However, with the need to handle high-pressure fluids, thicker pipes known as XS were introduced. Subsequently, XXS pipes were developed for even greater pressure requirements. The transition to more cost-effective thin-walled pipes led to the introduction of these weight classes. The relationship between pipe schedules and weight classes is detailed in ASME B36.10 and ASME B36.19 specifications.

Describing Steel Pipe Dimensions and Size Correctly

To accurately describe steel pipe dimensions, various methods are employed:

a. Expressing as "pipe outside diameter × wall thickness," such as Φ 88.9mm x 5.49mm (3 1/2” x 0.216”). Additionally, specifications may include length measurements like 6m (20ft) or 12m (40ft), denoting Single Random Length (SRL 18-25ft) or Double Random Length (DRL 38-40ft).

b. Using "NPS x Schedule," e.g., NPS 3 inch x Sch 40, NPS 4 inch x Sch 40, indicating the same size as above specifications.

c. Employing "NPS x WGT Class," such as NPS 3 inch x SCH STD, NPS 4 inch x SCH STD, which correspond to the sizes mentioned earlier.

d. Utilizing "Pipe Outer Diameter x lb/ft.," a common approach in North and South America. For instance, a pipe with an outer diameter of 3 1/2” would be described as having a weight of 16.8 lb/ft, where "lb/ft" represents pounds per foot.

In conclusion, understanding the nuances of Nominal Pipe Size (NPS), Nominal Diameter (DN), and Pipe Weight Class Schedule is crucial for accurately describing and specifying steel pipe dimensions.