There are many types and uses for pipes, and most of them are round in shape. This can’t be a coincidence so I decided to research why pipes are made round rather than square. 

It surprised me to learn that pipes are round based on significant strength, performance, and cost advantages over square pipes. Here are the top 5 reasons why pipes are round, and despite these reasons why sometimes we use square pipes. 

5 reasons why pipes are round

Round pipes are stronger, more efficient, safer, and cheaper. How can they be though? Read on to find out: 

1. Withstanding pressure 

Pipes with a circular cross-section can withstand high pressure. Far higher than a triangular or square pipe. 

The force of the water is distributed evenly along the whole pipe meaning there are no weak spots. Each square has a weak point in the middle. 

2. Flow of volume

Liquid flows faster through round pipes compared to angular pipes. 

A pipe with angles requires more frictional resistance than a round pipe. And frictional resistance slows down the flow and puts more stress on the pipe. 

Round pipes are the best for volume-to-surface area ratio. This means the internal area of the pipe that is in contact with the liquid is less for round pipes than in other pipes. 

3. Prevent rusting/degradation of the pipe

With a round pipe, water flows evenly. In a pipe with angles, water flow is not even and there will be certain areas within the cross-section where water flows slower. Physics.aps.org notes ‘the flow is faster in the middle than nearer the walls’. 

Slower moving water in angled pipes can cause rusting of the section which damages the pipe and can contaminate water. 

4. Cheaper to produce

Less material is required to produce round pipes vs square pipes. 

Round pipes have the largest inside area to perimeter ratio than any other type of pipe. To produce a pipe with a flow rate of 10 feet per second, a round pipe requires less material compared to square or other pipes. 

5. Fixtures and fittings

Due to having greater performance and being cheaper, round pipes have widely been used for many many years. 

This means that pipe fittings are now all made for round pipes. Why would anyone produce a square pipe when it’s less efficient and there aren’t any existing fixtures for it? 

Are all pipes round? 

It’s very rare to find square fluid pipes. The application would need to be low pressure in order for the pipe to withstand the internal pressure (and not fracture at the angles). Ankara University note:

‘Noncircular pipes are usually used in applications such as the heating and cooling systems of buildings where the pressure difference is relatively small, the manufacturing and installation costs are lower, and the available space is limited for ductwork’ 

However, square PVC water pipes do actually exist. Interestingly, the use for this particular pipe is for a ‘poultry nipple system’ which is a device that gives water to chickens. This would be a low-pressure delivery system and is the only square water pipe I could find. 

The main use for square tubing is in construction. Examples include building construction, signposts, and railing.

The advantage of using square vs round piping is that square piping is easy to connect flush to other materials. It’s easier to weld on the flat surface of square tubing compared to round pipes. 

Builders can also easily drill into square pipes, making it easy to build metal structures.   

Which are stronger, round, or square pipes? 

Round pipes are inherently stronger than square pipes.

For any kind of high-pressure flow, round pipes are far stronger. There are no weak points whereas angled pipes always have weaker points (the part of the pipe furthest away from the angle). 

Round pipes offer far superior performance and cost efficiency vs square pipes.

Round pipes also offer superior strength in construction. And many constructions do use round pipes. Look at scaffolding for example – almost all scaffolding uses round piping.  

However, typically construction piping is made from mild steel which is incredibly strong. The practicality benefits of using square piping vs circular piping normally outweigh the strength. 

Conclusion

Round pipes are considered superior in most cases. Strength, performance, and cost are reasons why we see round pipes more regularly than square pipes. It’s extremely rare to see a square pipe used for any kind of delivery of fluids. 

Sometimes square pipes are used in construction where pipes need to be welded or drilled together. And due to straight line edges, square pipes can be well suited to constructing building frames.