Deciding between PVC-M and PVC-U pipe for water transport in grain irrigation

Roland Andrag, Agrico CTO
Published: 31 May 2022

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PVC pipe remains the most economical way of transporting irrigation water, despite recent increases in the price of plastic. Agrico has recently started manufacturing modified PVC (PVC-M) pipe in addition to unmodified PVC (PVC-U) pipe that it has been manufacturing for more than 30 years. Let us help you understand the difference between PVC-U and PCV-M pipe, and the trade-offs involved in choosing the best pipe to transport your water.

Our in-house factory produces and sells more than 2 000 000 m of PVC pipe per year.

Why are PVC pipes important in the grain industry?

A large portion of South African grain is produced under irrigation. Pipe makes up a significant portion of the cost of irrigation systems. Agrico estimates that South African farmers currently spend in excess of R1b per year on pipe.

PVC pipe is widely used in the transportation of irrigation water. It is resistant to corrosion and in most cases more economical than galvanised steel, HDPE or glass fibre reinforced pipe. PVC-U and PVC-M remain the two most popular PVC options.

PVC-U is commonly used in agriculture and industry. First introduced in 1935, it has proven to be economical, durable, corrosion free and easy to install. PVC-M is manufactured by combining PVC resin with a toughness enhancing agent during the manufacturing process, making it resistant to impacts and shocks.

Agrico PVC-M and PVC-U pressure pipe conforms to the SANS 966-1 and SANS 966-2 standards, respectively, and is certified as such.

How does PVC-M compare to PVC-U?

Toughness
Irrigation pipes are often damaged during delivery and installation, leading to serious problems later. PVC-M is tougher and more resistant to impact than PVC-U, and thus less likely to be damaged before or during installation. Its toughness also makes it more resistant to pressure surges during operation, which may occur when pumps are abruptly started or stopped, such as during load shedding, or valves are suddenly opened or closed.

Safety factor
The safety factor of a pipe is the ratio of the maximum pressure it is expected to withstand in service to its normal rated working pressure. PVC pipe specifications require a high safety factor due to the fact that the pipe is exposed to many stresses other than the internal water pressure. These stresses include rocky terrain, rough handling and installation and poor pipeline design which may cause pressure surges during operation. Since PVC-M pipe is tougher, it is more resistant to these external factors, and thus the specifications allow for a lower, less conservative, safety factor than that specified for PVC-U. This lower safety factor (see Table 1), allows PVC-M to have a thinner wall than equivalently rated PVC-U pipe. A material saving is realised.

While PVC-M pipe is more resistant to damage during transport and installation, the lower safety factor employed in its specification makes it more important that due care is taken when the system is designed, so as to avoid pressure surges caused by phenomena such as water hammer during operation. Mitigation measures include proper deaeration of pipelines and driving pumps with VSDs (variable speed drives) so that they start gradually and that pressure can be controlled.

Table 1: A comparison of various classes of PVC-U and PVC-M pipe.

Cost
When considered kg-for-kg, PVC-M pipe has a more expensive formulation and is more expensive to manufacture due to more intensive processing required. However, the reduced safety factor more than makes up for this, so that, depending on the size and pressure class required, PVC-M pipe is between 15 and 25 % less expensive than equivalent PVM-U pipe at the factory gate.

Recent increases in the price of PVC raw material have strengthened the case for PVC-M. Simply put, PVC-M pipe has a thinner wall than PVC-U pipe of the same pressure class and diameter, uses less material, and costs less.

Agrico supplies an extensive range of piping for seamless water transportation.

Agrico PVC pipes – in-house manufacturing with over 30 years of experience

At Agrico, we don’t believe in beating around the bush. We understand that the optimal solution has to be a cost-effective one. As the oldest remaining manufacturer of PVC in South Africa, we have over 30 years of experience in providing elegant high quality PVC pipe at the lowest cost.

Agrico offers irrigation pipe manufactured in-house as well as pipe from other top producers for seamless water transportation. We supply the full range of PVC-U and PVC-M pipes in all standard diameters (from 20 mm all the way up to 630 mm) and pressure classes (from class 4 up to class 25). We carry extensive stock, ready for sale and delivery.

To find out more about PVC and other irrigation pipes, or for a quote, send an e-mail to sales@agrico.co.za, or visit their contact page at www.agrico.co.za/contact.