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Size Standards for Stainless Steel Pipe


What are the standard sizes for stainless steel pipe?  What does schedule mean, and why is it used when talking about pipe sizes?  These questions and more will be examined in today’s post.

Stainless steel offers several advantages over other metals, and these benefits make it an excellent material for a variety of demanding applications.  Whether it’s superior strength, corrosion resistance or ease of manufacturing, more solutions are relying on stainless.

That’s why understanding the sizing system for pipe is important.  It’s also why working with an experienced material supplier who knows the industry terminology is critical.

What are the advantages of stainless steel pipe?

There are two primary attributes that make stainless steel extremely attractive for a wide variety of industries: excellent strength and corrosion resistance.  This is especially true when talking about stainless pipe.  Other benefits include stainless steel’s thermal and chemical resistance, cleanliness and lower maintenance costs.

When picking out a material, you’ll need to take careful stock of the specific requirements for your field and application. Stainless offers tremendous strength, versatility, weldability and a lack of reactivity to several chemicals, making it a primary choice for pipe material.  Another benefit that’s often overlooked is that it requires a significantly lower preparation time prior to fabrication compared to carbon steel.

When working in a high temperature environment, stainless is a great choice; it’s also resistant to UV radiation.  Combining these attributes with its excellent corrosion resistance, stainless steel is often the only option when dealing with marine or other extreme environments.  It’s even possible to apply treatments that make stainless pipe resistant to microbial growth. Stainless is commonly used in the food and beverage, wastewater treatment and healthcare industries.

Another lesser known but valuable trait is that stainless equipment tends to retain its resale value as it ages.

Seamless Versus Welded 

When picking out what type of stainless steel pipe to use, one of the decisions to make is whether seamless or welded is required.  In general, welded pipe costs less and is more readily available than seamless, as it’s easier to manufacture. However, depending on the application, welded piping may not be an option.  The weld’s seam is a weak spot in the pipe, creating a risk of rupture in pressurized applications.  Recent advances in manufacturing techniques have improved welding integrity, but it is still an issue. Pressure-related specifications will need to be followed prior to settling on materials.

When picking a material, options will likely include aluminum, copper, carbon steel or plastic.  Aluminum, while it’s lightweight, is not as easy to weld and typically is not as corrosion resistant.  Copper is durable and heat resistant, but much more expensive. Carbon steel is prone to corrosion, while plastic rarely can match the durability afforded by stainless steel.

What do we mean by pipe schedule and nominal pipe size?

The size of pipes can be described in several different ways.  Consider a pipe’s outside diameter, wall thickness and inside diameter; when purchasing pipe, there are two size indicators that figure all the above at once.  These are the nominal pipe size and the schedule number.  Industry standards to refer to pipes by their schedule, such as schedule 40 and schedule 80; these are among the most common sizes.

In 1927 the American Standards Association created a system that designated wall thicknesses based on steps between the sizes. The nominal pipe size is referenced, and the term schedule was invented to specify the nominal wall thickness of pipe.

First, the nominal pipe size refers to the outside diameter.  Typically, this won’t be an exact measurement, but a reference number that can be used to figure out the exact dimensions. Complicated right?  As an example, if the nominal pipe size is 3, then the actual outside diameter should be 3.500 inches, and an NPS of 2 indicates the outside diameter is 2.375. Please follow this link to access a chart with the various standard diameters here:

Knowing only the nominal size doesn’t indicate much about the pipe.  Equally as important is knowing the pipe schedule. The schedule determines both the inside diameter and the wall thickness for a nominal pipe size.  Likewise, only knowing the schedule without the nominal pipe size also does not provide enough information.  With the nominal size and the schedule, one can figure out the exact wall thickness, as well as both the inside and outside diameters of the pipe. 

What are the differences between Schedule 40 and Schedule 80 piping? 

As mentioned, schedule 40 and schedule 80 are probably the two most common pipe schedules.  The major differences between the two include wall thickness, inside diameter and weight.  Schedule 80 has a larger wall thickness, smaller inside diameter and increased weight when compared to Schedule 40, assuming they both have the same nominal pipe size. 

The above referenced chart includes sizing information for the various standard schedules, which range from schedule 5 to schedule 160.

Your Technical Services Provider

When it comes to pipe size, there are many options to choose from.  When determining what schedule pipe and what material is just right for the next project, why not team up with the professionals?  Clinton Aluminum’s dedicated team of experts has the experience and familiarity to answer all questions about pipe dimensions and materials.  Contact us today to speak with one of our knowledgeable and friendly representatives.


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