Chemicals trump technology. Alright, but what does that mean? Well, you may have the best sensor technology for your application, but it won’t help you if the material used for your sensor is not compatible with the chemicals you are measuring. In short, you need good chemistry between your materials and your chemicals. It’s not as easy as it sounds.
For the purpose of this article, chemical compatibility refers to chemicals and materials that do not react with each other. When you have poor compatibility your sensor will physically breakdown, leading to at least sensor failure, and possibly a breakdown of important equipment and a chemical spill.
Failure to check chemical and material compatibility can result in disastrous consequences. With that said, here are a few general rules and guidelines to help you find a starting place in your research and testing. Let’s start with a look at some common materials.
Stainless steel is great for a lot of applications, such as diesel fuel. However, for acids and oxidizers, e.g. sulfuric acid, phosphoric acid and bromine, stainless steel is not a good option. The acid will corrode the steel and affect the integrity of the sensor. Not all acids are the same, and not all have an adverse reaction with stainless steel, so before you rule out stainless steel as an option for your application research more specific chemical compatibility. We like the Chemical Compatibility Database from Cole-Parmer due to its extensive archive and user-friendly system.
Materials such as polypropylene and polyurethane are an excellent option for chemicals such as chloride and sodium hydroxide. They do not, however, play well with halogenated and aromatic hydrocarbons such as fluorine, chlorine, benzene and toluene.
Teflon, Polyvinylidene fluoride, etc.
What about exotic alloys and Teflon or even PVDF (polyvinylidene fluoride) otherwise known as Kynar®? It is fair to say that materials such as Teflon and PVDF are compatible with a majority of chemicals. However, they also come with a larger price tag and are may not be available for particular sensor types. Fortunately, there are a number of ultrasonic sensors available with PVDF on the exposed sensor face.
But wait, there is more. For sensors with transducer faces made of PVDF, the mounting threads are typically polycarbonate. If certain chemicals come into contact with this material, the sensor would be damaged. For certain types of acids and chemicals where you are using an ultrasonic sensor we recommend considering an ultrasonic sensor that has both a transducer face and mounting threads constructed of PVDF. This way the sensor is completely protected.
Whenever you are looking at chemical compatibility you must be aware of the chemical’s temperature. A material may be fine in one temperature range but will break down in another. Sensors with stainless steel generally handle higher temperatures better than their plastic counterparts.
Checking for Chemical Compatibility
There is a lot of information here to consider, so take it one step at a time:
- Identify the exposed materials of your potential sensor: transducer face, threads, body, etc.
- Identify the solutions, liquids, and/or vapors the sensor will come in contact with.
- Cross check the compatibility of each interaction, using MSDS sheets, a compatibility database, or other guide.
As you can see, these guidelines are very general and there are plenty of exceptions. We recommend you consult with other resources such as chemical compatibility guides like Cole-Parmer or others published by chemical companies.
Keep in mind, though, that even a reputable resource will almost always recommend you do your own testing before you initiate a full system installation.
If you have questions regarding chemical compatibility, give us a call, send us an email, or Live Chat with us. We have a lot of experience with different chemicals, and we may have a good answer for you. If not, we can walk you through a chemical compatibility guide to help you find a probable match.
Harsh conditions putting the pressure on you? Our PT-400 has CSA, ATEX, and IECEx certifications. Check it out for yourself: