This is an updated version of the product training course introduced by Supply House Times in 1979, authored by Don Arnold.

The College of Product Knowledge ran in Supply House Times for three years and resulted in a reprint manual that sold for many years to follow, totaling thousands of copies. It became something of an industry classic. Much of the original training material is still applicable to the products sold today - but there is also much in the wholesalers' product mix that is new since then. The purpose of this updated series is to look at what has come along since the first edition.

In this current series of College of Product Knowledge articles, some of our coverage will take the form of updates on what's come along in terms of new products and trends since the original edition (like the recent two sections on residential faucets). There are other categories, like the one beginning this month, where "what's new" isn't so much the products as it is the reader - in the sense of being new to our industry. In these categories, we will be providing a condensed review of the basics involved. This month starts a sub-series of installments concerning supply piping, with a specific look at the steel variety.

General Considerations Of Supply Piping

Piping is the most basic aspect of a plumbing system - a network of conduits that carries fresh water to, and wastewater from, the points of usage. To be approved for use in such applications (in both the functional and code-approval senses), supply piping must meet several requirements, including:

Potability: (Pronounced "poat-ability.") In plain English, this means "safe to drink from" - not releasing harmful chemicals or particles into the passing water.

Strength: Often defined as bursting pressure or psi rating, the piping material must be strong enough not only to withstand the pressure of the water being supplied in normal conditions, but also be able to handle periodic shocks several times greater.

Size And Capacity: The size of piping used in a given installation is important from the standpoint of delivering water to the points of outlet at the needed flow rate (gpm - gallons per minute). Undersized piping not only can result in slow delivery, it can be noisy, as well.

Resistance To Corrosion And Scaling: The water that is best for drinking can also be the hardest on the piping system. Scaling refers to buildup of accumulated minerals.

Temperature Characteristics: This is a consideration relating primarily to plastic piping. There are types suitable for both hot and cold water - others that are designed for cold water only (the latter subject to a degrading of strength and other properties when temperatures exceed a certain level).


Though steel pipe has the longest history of use in this country, there is still a good deal of confusion about what it is - and isn't. Since the most common means of joining steel pipe is by use of threaded joints, some people mistakenly think that any material that is threaded is steel. Within our industry we have a common term, "IPS," meaning "iron pipe size," that is often applied to steel pipe. Does this mean that iron pipe and steel pipe are really the same thing? No. Without getting into all the background on how we ended up with this confusion of terms, let's just say that IPS today refers to a standard of pipe sizes and thread dimensions, not to the material a particular pipe is made of.

Advantages Of Steel Pipe

Strength And Ruggedness - not easily crushed or damaged by rough handling - resists shocks and stress.

High burst strength - Handles pressure and shock factors of average installations many times over.

Dimensional stability at high temperatures.

Permits mechanically strong threaded connections, yet allows easy disassembly when necessary.

Can be butt welded - Two ends are brought together and welded around the seam.

Quiet service - insulates the sound of passing water.


Finishes And Coatings

In its natural form, conventional steel pipe will corrode. To protect against this, a process called "galvanizing" is used on the type intended for water usage. Galvanizing involves applying a thin coating of zinc over the steel that prevents corrosion both by keeping moisture away from the underlying steel, as well as creating a minute electrical (galvanic) action. Galvanized pipe has a characteristic grey color. Unfinished steel pipe (not galvanized) is black and should not be used in plumbing applications because of its lack of corrosion resistance. (Black steel pipe is commonly used for non-water applications, such as gas and air.)

Weight Classes and Steel Pipe Sizes

In addition to the standard weight class of piping commonly used in most plumbing applications, two strength grades made with thicker walls may be used for certain industrial installations - extra strong and double extra strong.

Steel pipe sizes can be confusing. In a nutshell, be aware that the designated sizes of steel pipe are not the actual sizes. If you go out back with a ruler looking for the ?-inch pipe, for instance, you won't find anything that size, whether you're measuring across the inside or outside. When it comes to pipe measurements, the actual is always larger than the nominal size (it's a good idea to have a chart of equivalent sizes handy). Exceptions: when you get up to sizes 14-inches and larger, designations are based on the actual measurements. (I said this was confusing.)

Pipe Threads

It may not be obvious at a glance, but the threads used on steel pipe (in the U.S.) are tapered - 1/16th of an inch-per inch, to be exact. After the threads are cut, they measure smaller in diameter at the end of the pipe. Not all pipe threads are the same, either in terms of the number cut per inch, or in the depth to which they are cut. In other words, these are factors that vary with the size of the pipe involved.

Common Measurement Terms For Piping

There are three common dimensional references used with piping:

I.D. (Inside Diameter) - the distance across the inside opening of a section of pipe or tube.

O.D. (Outside Diameter) - the distance across the outside of a section of pipe or tube.

Wall - the dimensional thickness of a section of piping material.