Posted at 26 June 2019

Choosing the Right Chemicals Pump

Paul Skade
By Andy Cruse
Technical Director, Flow Control

I joined ERIKS in 1999 and have over 35 years’ experience in the pump industry. Originally from a service/repair background I have worked in many roles and enviro...

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Choosing the right chemicals pump is a matter of concentration. While everyone knows that sulphuric acid, for example, is exceptionally corrosive, its corrosiveness depends on its concentration and temperature. So which material to choose for a pump when sulphuric acid is the pumping medium is not as simple as it might seem.

munsch pumps

 

If the sulphuric acid is being pumped for a particular process, you’d presume the concentration would be consistent. But the truth is very different. For example, simply cleaning the process equipment may leave some residue of other liquid, and when the acid starts to flow through the system again its concentration will be changed through contamination.

Suddenly, the material the pump is made from – selected to be resistant to a certain concentration range – will become unresistant, and the pump will start to corrode. Even worse, if the pump is metal and the surface corrodes, the corrosion will build-up until it is washed off or falls off. This leaves a fresh surface for the corrosion process to start all over again, and again, and again. Now corrosion turns to erosion, as the material – and the pump – are gradually eaten away.

Clearly, choosing the right material to cope with the correct range of concentrations at a given temperature is essential. And when an international chemical group made the wrong choice, they paid the price in more ways than one.

Nothing to smile about

Titanium oxide (TiO2) is a pigment used to make products such as toothpaste look whiter and shinier. It’s manufactured by hydrolysing titanium oxide sulphate to produce TiO2 and H2SO4 (sulphuric acid).

For the chemical company producing the titanium oxide, it was the sulphuric acid

by-product which caused the problems with their process pumps.

The pumps are required to run continually at a temperature of 110°C, pumping sulphuric acid at 30% concentration. However, the Hastelloy nickel-based steel alloy pumps were failing frequently due to corrosion and erosion, and the cost of downtime was compounded by the high cost of replacement Hastelloy parts.

In their search for a solution they approached Munsch to assess the possibility of replacing the metal pumps with plastic.

Putting the “P” in pumps

As specialists in plastic pumps, Munsch offer their NP range in a choice of polypropylene (PP), polyethylene (PE) and polyvinylidene difluoride (PVDF).

Whereas most metals are only resistant to sulphuric acid corrosion across a narrow concentration band, Munsch plastic pumps are resistant from 0% to 98% concentration. Whilst PP and PE materials are chemically similar, PE provides better erosion protection, but with an upper operating temperature limit of 85-90°C. PVDF provides slightly less protection against erosion, but is suitable for the operating temperature of 110°C in this customer’s application. And since it eliminates corrosion, it also prevents erosion.

The customer installed the recommended NP pump in PVDF for a trial period, after which they added a number of identical units. All the pumps have now been running for several years with no signs of corrosion or erosion, and can be expected to run for as long as 20 years without failing.

Simply, the best

The design philosophy behind Munsch pumps is all about simplicity.

Designed to be as easy as possible to assemble and disassemble, there is literally only one way to put a Munsch pump together. This means there’s no risk of a leak from a wrongly-assembled pump.

The non-metallic mechanical sealing system is also simplified for flexibility and cost-efficiency.  A single mechanical seal can be operated in single, double, shutdown flush or continuous flush operating modes, and the same seal size will fit all Munsch pumps. Again, this eliminates the risk of error in assembly, as well as reducing inventory costs and simplifying repair and maintenance.

By concentrating on manufacturing simply the best plastic pumps, Munsch leave their customers free to concentrate on their processes, without fear of pump failure.

 

Liked this article? You might want to read Know+How Magazine Issue 37, packed with related articles and more!

It's not just external surroundings that contribute to an aggressive environment, materials that are being processed and what goes through your equipment can also put assets under strain. 

We take a look at some of the issues you face on a daily basis and how to mitigate some of the risks. 

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