What is the difference between schedule 40 and schedule 80 PVC pipes?
In our day to day lives, a schedule simply means a plan of carrying out certain tasks within a given time duration. Scheduling is however a very different concept in plumbing.
If you are in the market for PVC pipes, the 2 terms you will be bombarded with are schedule 40 and schedule 80 PVC pipes.
So, what is the difference between schedule 40 and schedule 80 PVC pipes? And where is each applied?
The main difference between schedule 40 and schedule 80 PVC pipes is their wall thickness. Schedule 80 PVC pipes have thicker walls than schedule 40 PVC pipes (of the same outside diameter) and are therefore stronger and able to handle more pressure.
In terms of applications, schedule 40 PVC pipes are used in residential drainage (like sewer lines) while schedule 80 PVC pipes are used in commercial and chemical applications due to their thick walls and therefore high pressure rating.
Although schedule 40 and 80 PVC pipes have the same outer diameter and therefore easy to connect, they should not be mixed. Schedule 80 PVC pipes are used for high pressure applications and mixing them with schedule 40 fittings compromises the integrity of the entire pipe network.
As we are often reminded, a pipe is only as strong as its weakest link. If you therefore mix a schedule 80 PVC pipe with a pressure rating of 400 psi with a schedule 40 fitting with a pressure rating of 280 psi, the overall pressure rating of the entire pipe network is 280 psi.
Having said that, I don’t see a problem using a schedule 80 PVC pipe or fitting in a pipe network with schedule 40 PVC pipes. In short, you can higher but not lower.
Although not always the case, schedule 40 PVC pipes are mostly white in color while schedule 80 PVC pipes are grey. It is however important to check the pipe’s label to be sure since some manufacturers deviate from this practice.
Scheduling In Plumbing
Most people confuse scheduling in plumbing because of terms like wall thickness, outside diameter, inside diameter, width, nominal size etc.
You however don’t need to be confused. It is a very simple concept developed by the American Society for Testing and Materials (ASTM).
In plumbing, scheduling simply refers a standard which outlines how thick a pipe’s wall should be, relative to its width, also known as diameter.
As I have already mentioned, a schedule 40 pipe has thinner walls than a schedule 80 pipe of the same nominal size. Simply put, as a pipe’s schedule increases, its wall thickness increases as well.
It is important to understand that scheduling does not affect the outside diameter of a pipe. The variable in all this is the pipe’s thickness which directly corresponds to the inner diameter.
Needless to say, a schedule 40 pipe will have a larger inside diameter compared to a schedule 80 pipe of the same outside diameter. The schedule 80 pipe will however have a higher pressure rating than the schedule 40 pipe.
To put this into perspective, a 2-inch schedule 40 PVC pipe will have a 0.154’’ minimum wall thickness and a pressure rating of 280 psi while the same size of a schedule 80 PVC pipe will have a 0.218 minimum wall thickness and a pressure rating of 400 psi.
Pipe scheduling is important in determining what kind of pipe is best suited for a certain application. This should tell you that no pipe is better than the other but it actually depends on where the pipe will end up being used.
The Difference Between Plumbing PVC and Electrical Conduit PVC
PVC pipes are not only used in plumbing but also in electrical applications. However, the PVC pipes used in plumbing are not the same pipes used in electrical installations.
The main difference between plumbing PVC pipes and electrical conduit PVC pipes is that plumbing PVC pipes are pressure-tested while electrical conduit PVC pipes are not. This means the two pipes cannot be used interchangeably.
And it makes perfect sense. In plumbing PVC pipes, there will be fluids flowing inside the pipes under pressure and you therefore want to be sure that the pipe can withstand the pressure.
On the other hand, electrical current is never under any pressure and the pipes are only there to protect the cables. Pressure-testing these pipes is therefore not of any importance.
It is therefore very important to let the hardware store know what exactly you need to do with the pipes to ensure that you buy the right pipes.
Having said, there will be no harm in using plumbing PVC pipes in electrical applications. You however cannot use electrical conduits PVC pipes in plumbing applications.
Schedule 40 PVC pipe is better than schedule 80 PVC pipes when used as an electrical conduit since it has a larger internal diameter which makes pulling wires through it easier. It is however a good idea to use schedule 80 PVC pipes in high traffic areas to prevent damages thanks to its thick walls.
Schedule 40 vs Schedule 80 PVC pipes
Let us now dig deeper into the major differences between schedule 40 and 80 PVC pipes.
1. Wall Thickness
As I previously mentioned, wall thickness is the main difference between schedule 40 and schedule 80 PVC pipes. To help you remember it, just know schedule 80 pipes have a thicker wall have a larger wall thickness than schedule 40 pipes.
This therefore means that more material is used to make schedule 80 PVC pipes which make them stronger and rigid compared to schedule 40 pipes. As a result, they are able to withstand more pressure than the schedule 40 pipes of the same outside diameter.
Schedule 80 PVC pipes are used in industrial and chemical applications where they meet and even exceed the require pressure requirements of the fluids they transport.
An important point to remember is that PVC, being plastic is affected by heat. A pipe with thin walls will easily be softened by hot fluids while a thick and tough pipe will hold just fine, which is why schedule 80 PVC pipe are well-suited for industrial applications.
It goes without saying that schedule 80 PVC pipes have a smaller internal diameter than their schedule 40 counterparts. That means reduced volume of the liquid being transported when comparing pipes with the same outside diameter.
This should however not be a big concern since you can opt to use a slightly large pipe if you have a lots of liquids to move.
For instance a 2-inch (nominal) schedule 40 PVC pipe has an internal diameter of 2.047 inches wile a 2-inch schedule 80 PVC pipe has an internal diameter of 1.913 inches. If that is not sufficient for your application needs, you can opt to go with the 2-1/2’’ pipe with an internal diameter of 2.29 inches.
2. Pressure Rating
The pressure rating of both schedule 40 and schedule 80 PVC pipes is directly proportional to their wall thickness. The pipe with the thicker walls (schedule 80) will withstand more pressure than schedule 40 pipe before, bursting.
There is one thing I don’t want you to misunderstand though. In the case of schedule 40 and 80 PVC pipes, we are not talking about the pressure of the liquid inside the pipe, but the pressure limit of the pipe.
It is common knowledge that liquids have a high pressure when flowing through thin pipes compared to large pipes.
Now, although schedule 40 and 80 PVC pipes are of the same nominal size, schedule 80 pipes have a smaller internal diameter which means liquids flowing through a 2-inch schedule 80 pipe will have a high pressure than those flowing through a 2-inch schedule 40 pipe.
That is not the pressure that matters in this case. What matters is the pressure the pipe can withstand before it bursts.
These tests are usually carried out in controlled environment and if for instance a certain pipe is rated 400 pounds per square inch, it does not mean it will burst at that pressure. There is usually a safety net. Such a pipe would probably burst at between 450 and 500 psi.
Due to the extra wall thickness in schedule 80 PVC pipes, more PVC materials is needed to make them compared to schedule 40 PVC pipes. As a result, schedule 80 PVC pipes are more expensive compared to schedule 40 pipes.
The extra pipe used to make schedule 80 PVC pipes also makes them heavier compared to schedule 40 pipes of the same size. They are therefore harder to install which means more people will be involved in handling them.
You shouldn’t however choose a pipe schedule based on cost. Consider your needs first then purchase the pipe with the appropriate schedule.
Traditionally, schedule 40 PVC pipes are while in color while schedule 80 PVC pipes are grey. That is however not always the case as some manufacturers deviate from this norm and it is importantly not a code requirement.
It is therefore always important to make sure that you properly indentify the pipe before purchasing it. Good thing is that the pipes are always labeled with the specific schedules indicated.
Schedule 40 vs 80 PVC Pipes Comparison Table
|Nominal Pipe Size (inches)||Internal Diameter|
|Pressure Rating (psi)|
|Pressure Rating (psi)
Which Schedule of PVC Pipes Should I use?
Although I have said that schedule 80 PVC pipe have thicker walls and therefore higher pressure rating, that does not mean they are the best pipes to use. Each schedule of pipes has its places where it is best suited.
If you have a project that is industrial or one involving chemical process, schedule 80 PVC pipes are what you should go for.
For someone looking to install pipes in the house in the drain waste and vent system, schedule 40 PVC will be ideal, Not only will they meet and exceed your pressure specifications but they will also save you some money.
As you shop for the pipes, do not forget that the fittings also come in the 2 schedules. That means that if you decide to work with schedule 40 PVC pipes, all the elbows, tee and couplings should also be of that schedule.
Related: PVC vs ABS pipes
And basically those are the difference between schedule 40 PVC pipes and schedule 80 PVC pipes. I hope this guide was helpful.