The mainline pipe is one of the most important components of any irrigation system, whether it be a simple system used for maintaining a sports field or a large and extensive system used in farms and nurseries. The mainline pipe consists of the piping that connects your water source with the water control valves that operate your sprinklers and water guns, and as such, they are held under constant pressure and are constantly filled with water.

As you can imagine, the structural demands placed on this pipe are quite high, so choosing the right material for your mainline pipe is vital -- choosing an unsuitable material can lead to corrosion, leaks or even splitting, which can be messy, difficult and expensive to repair. The following materials are all commonly used to manufacture mainline pipes, and each comes with its own distinct advantages and disadvantages.

PVC

PVC is a tough and versatile thermoplastic used in a wide variety of piping applications and can be well-suited to mainline construction. Far tougher and more durable than you might expect from a humble plastic, PVC irrigation pipes are also immune to corrosion and possess a small but important amount of flexibility, which allows them to resist the internal stresses of constant water pressurisation. PVC piping also tends to be relatively cheap, especially compared to high-end metal piping.

However, choosing PVC piping for your mainlines can be a poor choice if you expect your irrigation system to bear heavy weight, such as heavy farming vehicles driving over buried irrigation systems. PVC has limited load-bearing strength and and quickly crack and collapse under excessive loads. You should also bear in mind how much of your mainline will be exposed to the elements, as PVC can perish and lose strength quickly if exposed to large amounts of intense sunlight.

PE

PE is another type of thermoplastic, but it possesses less strength and much more flexibility than PVC, making it an excellent choice for low-capacity mainlines that regularly experience heavy loads from above. This flexibility also allows it to be sold in long, versatile coils which are easy to fit and inexpensive to purchase, requiring fewer connection components that may become weak points in your mainline. 

Unfortunately, PE piping tends to have a relatively low pressure threshold and is not suitable for large-scale, high capacity systems that work under high pressures. The flexibility of PE also means that connectors have to be made from other materials such as galvanised steel, which may corrode and become unusable more quickly than the piping itself.

Metal

Metal piping has long been prized for its suitability for irrigation mainlines, and it's easy to see why -- extremely high pressure ratings and remarkable durability mean that a well-maintained metal mainline can last for years. However, no two metals are ever quite the same, and your choice of metal can dramatically affect how your mainline performs:

• Steel pipes are inexpensive and incredibly strong, with maximum pressure ratings unrivaled by most other piping materials. They are also simple to put together, with easy-to-use connectors that use threading and clips to make connecting individual pipes quick and easy. However, steel is vulnerable to corrosion, which can dramatically reduce your mainline's strength and cause a buildup of sediment within the mainline that reduces pressure and efficiency. Steel piping with protective galvanised or powder coatings are more resistant to corrosion, but also more expensive.
• Aluminium pipes are simple to use and are highly resistant to corrosion, while maintaining enough strength against high pressure and heavy loads to withstand most commercial applications. However, they have less overall strength than steel mainline pipes and tend to be considerably more expensive. 
• Copper pipes are immune to corrosion and all other forms of natural damage, and can be expected to last for the lifetime of your irrigation system without repairs or replacements. However, this malleable metal possesses less strength against internal and external forces than either steel or aluminium, and may not be suitable for heavy-duty applications.