An Overview of Piping Codes
Working with piping codes is a little like doing your taxes. The calculations can be fairly complex, and you will spend a lot of time flipping back and forth between different sections that refer to yet other sections. And if you don’t know where to look for the information, you’re likely to overpressurize!
There are lots of piping codes in use throughout the world. Some countries, like Canada, take advantage of the considerable body of knowledge contained in the US codes.
In the US, we follow the ASME Code for Pressure Piping, B31. The code was first published in 1935 by the ASA (American Standards Association, now known as ANSI, the American National Standards Institute). The responsibility for developing the code was assigned to the ASME (American Society of Professional Engineers).
The ASME Code is so extensive that it was more convenient to break it up into several separate documents, which represent various industries. The code now consists of:
- B31.1 Power Piping
- B31.3 Process Piping
- B31.4 Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids
- B31.5 Refrigeration Piping
- B31.8 Gas Transportation and Distribution Piping
- B31.9 Building Services Piping
- B31.11 Slurry Transportation Piping Systems
Piping codes are used by engineers and designers to design piping systems and system components. Contractors use the codes to construct piping systems.
Usually, by the time you get involved in a project, most of the piping specifications are written, and the codes to be used have been laid out in the specifications. But how did the guy who wrote the specs know which codes to apply? Much of the time, the answer lies in the codes themselves. The codes will explain what their intended scope is. But the codes are often applied to piping systems that are outside their scope.
This sounds like it might be a big problem, but the intelligent application of a piping code outside of its scope is not necessarily bad.
Let’s say that you are the engineer in charge of setting up the piping specs for a plant that is going to produce turbo-widgets for the up-and-coming e-widget industry. The heat is on to get into production right away, and the Chief Engineer is visiting you every 15 minutes to see if you have issued the specs for bid yet.
The first thing you notice after going to the code, is that the e-widget industry is not represented. And you can’t find any mention of piping systems used in the production of turbo-widgets.
But you know that the plant uses air for the turbo-stamping lines, it uses water to cool the ovens that bake the widgets, it uses hydraulics for the robots that assemble the turbo-widgets, and there is also high-pressure steam for heating the reactor vessels that produce the proprietary widget compounds.
Like many projects of this type, a review of the available codes indicates that your choices are probably going to reduce down to B31.1, B31.3, and perhaps B31.9. If some cooling processes are used in the process, you might have to rely on B31.5 as well.
Some of these codes are more stringent than others. For instance, the Allowable Stresses for a given piping material is less in B31.1 and B31.9, than it is in B31.3. It’s the same material, made the same way! But the Allowable Stresses are different. In this respect, B31.1 and B31.9 are more stringent that B31.3.
You can always apply a more stringent code than is required for an application. Doing that does not compromise safety.
So you could specify the most stringent code for all of these services, but that might mean that your 2″ diameter low-pressure cooling water lines would be constructed out of Schedule 160 pipe. And by the way, since 2″ Schedule 160 pipe has a wall thickness of 0.344″, the ID is reduced, and maybe you better use 3″ pipe so your head losses aren’t so high.
But the Chief Engineer isn’t crazy about the idea, since the piping costs are going to go way up. And a big part of engineering is doing the safest things in the most economical manner.
So you decide to use B31.1 for the steam and condensate systems only, and B31.3 for everything else. You might want to use B31.1 for high-pressure hydraulics lines, especially if they are in an area where corrosion is a factor.
Innovative Design Engineering of America, LLC specializes in writing piping specs, performing code calculations, and applying piping codes. We also do piping stress analyses for both static and dynamic loads. Contact us with your questions about piping systems and components.