Hastelloy compared to PTFE
Chemical pumps: The special alloy C22 withstands demanding flow conditions

Already available in various materials, now Crane Flow is expanding the application range of its DEPA air operated diaphragm pumps with a new material variant. The DEPA-HC made of the special alloy Hastelloy C22 has been designed for demanding applications, namely: situations where highly aggressive and, at the same time, abrasive fluids are to be transported in high temperature and pressure ranges. Even PTFE pumps give up under such conditions.
At Wacker, located at Burghausen/Germany, the DEPA-HC serves as a mobile “allrounder”.

A classic chemical pump must be well equipped to be resistant against corrosive, toxic and other critical substances. Only then can a pump convey product reliably and dependably – a central requirement in the chemical industry. Operators are just as focused on safety as on cost-effectiveness. Therefore, they not only place great importance on high reliability (key word: MTBF – Mean Time Between Failures), but also on the most favorable lifecycle costs. In an ideal situation, adequate investment should be combined with low operating costs. This is absolutely realizable with air-operated diaphragm pumps: compressed air is always available on the works premises, and the units (which are very light because they do not have an electrical drive motor) are mobile and quickly installed.
Efficient optimization of operating time

Alongside several plastic versions, the manufacturer Crane Flow has developed more than 20 metal variants for its air-operated diaphragm pumps. The newest is the HC-type made of Hastelloy C22 (2.4602), which will be introduced in detail in the following. The DEPA-HC made of the special alloy C22 is especially designed for critical applications in the chemical industry, namely: situations where highly aggressive and, at the same time, abrasive fluids are to be transported under high temperature and pressure ranges. Hastelloy combines an excellent chemical resistance with good mechanical properties and minimal wear.

This is an important advantage, especially in contrast to the PTFE pumps that are usually used with abrasive and aggressive substances. PTFE is less able to withstand pressure, and it is also problematic above all with regard to the deformation of material under load (cold flux). Background: PTFE consists of very long, linear carbon chains which are surrounded entirely by fluorine atoms. These shield the molecule sterically and thereby protect the molecule against chemical attacks. The high binding energy of the carbon-fluorine compound contributes to a very strong chemical shielding effect. However, increased pressure and/or higher temperatures cripple the substance. For the operator this means that PTFE pumps can leak at high temperature/pressure levels. If the substance must not for any reason come into contact with the surrounding environment, such plastic units cannot be used, or they have to be exchanged at relatively short intervals or subjected to costly repairs. In contrast, pumps made of Hastelloy C22 are considerably more resistant to pressure and/or temperature than PTFE and in general are more cost-effective. For the launch of these pump variants, Crane Flow offers two designs; the 10 and the 1 1/20 pumps (DL 25 and DL 40).
The immediate advantages of the metal DEPA air-operated diaphragm pumps of range M, type HC made of the special alloy Hastelloy C22 are:
- high chemical resistance,
- high temperature resistance,
- high level of mechanical stability by using massive cast components,
- high creep resistance which is maintained even under continuous load,
- very smooth surfaces with minimal wear,
- good cold properties,
- no cold flow under pressure,
- maximum of 7 bar permissible.
The massive cast components are, thanks to the most modern casting techniques, produced with very minimal tolerances. And so it is possible to offer the pumps in a variety of material combinations: There is the option of ordering variants with “components that come into contact with product made of Hastelloy/ control valve nickelized in aluminium” or “components that come into contact with product made of Hastelloy/air control unit of stainless steel or bronze”.
DEPA-HC as a mobile
multipurpose unit
For each application the consideration of “which pump to use?” begins at the so-called technical base, often at the level of the most cost-effective material variant. If the product is corrosive, then the decision will fall very quickly on a stainless steel or plastic pump. But sometimes, when chemical resistance is considered, a further alternative is only found with a special alloy metal. The process of choosing a pump can be demonstrated by using a concrete example of problem analysis at Wacker: A range of pumps of differing designs are installed at Burghausen/Germany where, among other things, fine chemicals are produced. The common denominator of all the pumps is that they are produced from resistant materials and that great importance is attached to their tightness against emissions. But what happens if one of these stationary units fails? A replacement in the form of a redundant pump is not always viable, so in such situations the Wacker engineers work with mobile pumps. The DEPA air-operated diaphragm pumps from Crane Flow are used here, among others. It is obvious that because these mobile replacement pumps cannot be designed for one specific substance, only the highest quality variants are used.
Up to now, that was the case with the Wacker plastic diaphragm pumps where the casing parts, which come into contact with product, are made of PTFE. But now Wacker has ordered pumps made of Hastelloy. The deciding factors were:
- The DEPA-HC maintains form stability even at high temperatures.
- The pump has already been approved for use in explosive environments and certified according to Atex 100a.
- The operator can combine the materials to be used as desired.
- Particularly under high pressure and temperature, the DEPA-HC achieves a considerably longer service life (more economical lifecycle costs) than the PTFE design.
- Permanent load strain results in cold flow with PTFE variants; the Hastelloy variants do not show this phenomenon.
- High mechanical stability as well as chemical resistance by using massive components.
- Suitable for severe applications.
An important aspect was the declaration regarding conformity with Atex 100a (regulation 94/9/EEC), which was received at an early stage from Crane Flow. This is because in Germany and other EU countries, after 1st July 2003, pumps for use in explosive environments may only be used if they have been certified in accordance with the new regulations Atex 100a. However, most plant engineers and operators already expect that equipment delivered for use in explosive environments should be in compliance with the new regulations.
Pumps, in the context of Atex 100a, consist of two units: the (electrical) drive motor – which has up to now already been covered by these regulations – and the non-electrical pump part. This is also where we now need to ensure that the material does not exceed the ignition temperature at any point.
By the way: potential hazards can also occur when, for example, pumps are operated outside of their determined operating range or if leakage occur. The operator of the pump has to make sure that these are avoided or recognized in good time. He can fulfil this obligation by using corresponding control and supervision systems – for this Crane Flow offers a range of possibilities for the DEPA air operated diaphragm pumps.
To sum up: The principle of air-operated diaphragm pumps has sustained itself in many industrial applications. Whoever has operated this robust type of pump just once under real working conditions quickly realizes that it is a pump to be appreciated. This applies in particular to the new Hastelloy design from Crane Flow. In comparison to PTFE, Hastelloy shows a considerably higher level of temperature resistance without any tendency to cold flow (with a comparably good chemical resistance). Metal DEPA air-operated diaphragm pumps of the range M, type HC made of the special alloy Hastelloy C22 therefore display good suitability for use in, for example, acid production and chlorination plants.
At Wacker in Burghausen, the mobile DEPA-HC is being used for the transfer of demanding materials such as organic fluids and also chlorine-containing hydrocarbon product in the “fine chemicals production area”. The pump serves not only as a temporary replacement unit when a stationary pump fails, but also in emptying containers – a mobile “allrounder”.