1. What is the importance of a clean probe?
Accurate measurements of process fluid density and viscosity are an important part of many industrial processes, and cleanliness plays a major role in obtaining accurate readings. Often the process fluid causes deposits and measurement probes should be cleaned to ensure accurate viscosity and density measurements.
Dirt, debris, sticking material, and other contaminants can interfere with the sensor operation and cause incorrect readings. The SR probes are a stable, robust sensor system that operates over a wide range of temperatures and pressures. The standard sensor is made of 316L stainless steel, which is one of the most widely used materials in manufacturing processes involving fluids.
The SRV and SRD sensors are based on a resonant sensing element that operates in the range of approximately 7-8 kHz. The sensor measures fluid properties in a layer of fluid surrounding the resonant element. The sensor measures what it is in contact with so it is important to ensure that fluid that is of interest is in contact with the sensing element at all times.
If the sensor sensing element gets coated with sticky fluid and solids, it is recommended that the sensor is cleaned. This cleaning often takes place in situ aka the sensor is cleaned along with the line or vessel it is installed in. However, at times it is desired or important to remove and mechanically clean the probe/sensing element.
Adherent films can be removed by using appropriate solvents and/or wiping with a cloth or paper. Under no circumstances should abrasives be used to clean the resonator, as these will change the geometry and destroy its calibration.
Do not use ultrasonic cleaners under any circumstance as that could damage the probe internal components.
2. Removing the coating with a solvent-saturated cloth or paper
Cleaning SR (SRV or SRD) probes requires a gentle hand and the right materials. To start, use a soft cloth to wipe down the SR probe thoroughly. Make sure to remove any grease or dirt buildup that may have accumulated on its surface. Then, dampen a clean cloth with warm water and mild dish soap. Gently wipe down the stainless steel probe with the cloth and rinse it off with clean water. Finally, dry the stainless steel probe with a soft cloth. With these steps, your SR probe will remain clean and perform its best.
When it comes to stainless steel probes, it's important to keep them clean in order to protect the material from corrosive elements. Washing stainless steel probes with warm water and mild detergent can help prevent corrosion. For tougher soils or stains, a stainless steel cleaner or vinegar-based solution can be used on the probes. It is important to remember not to use any harsh abrasives, metallic scouring pads, or steel wool as these can damage stainless steel surfaces.
3. Chemical compatibility for Stainless steel 316
When it comes to chemically cleaning the Rheonics sensors, there are many different chemical solutions available. The most popular solution is a mixture of water and detergent, which can help remove dirt, dust, and other foreign materials from the stainless steel surface. It is important to note that stainless steel should not be exposed to harsh chemical cleaners for long periods of time, as this can cause damage to the surface. Additionally, stainless steel should always be dried thoroughly after being chemically cleaned in order to avoid any corrosion.
The following table can be used to verify the compatibility with different chemicals:
A: Asphyxiant(Gas and vapor only)
Figure 2. Chemical compatibility table
4. Commonly used cleaners
4.1. Alkaline cleaning
Alkaline solutions can be applied to the Rheonics probe to remove water-soluble materials. Alkaline solutions dissolve the bonds between water-soluble molecules, allowing them to be drawn off the probe and away from the surface, keeping the probe clean.
4.2. Caustic (Sodium Hydroxide)
Sodium Hydroxide (Caustic Soda) is a strong base.
In a wide range of industries including investment casing, it is used for metal degreasing and cleaning.
Rheonics sensors made of stainless steel 316 are considered resistant to corrosion below 80 degrees Celsius, up to the limit of their solubility.
Up to the limit of solubility, they are resistant to sodium hydroxide at any temperature below 80 °C.
Stainless steel 316 material is susceptible to stress corrosion cracking (SCC) attack at higher temperatures. If service temperatures are limited to 95°C, this should not be an issue.
4.3. Acidic clenaing
The type of stainless steel and its metallurgical and physical characteristics must be considered when planning an acid pickling operation. Due to their different alloy compositions, stainless steels behave differently when exposed to pickling acids. Parts made of stainless steel that have been sensitized by welding or thermal treatment, or that are highly stressed, are particularly susceptible to corrosion. Always monitor any corrosion effects and plan calibration and maintenance/replacement accordingly.
The corrosion resistance of stainless steel (passivity) is typically promoted and preserved by nitric acid; that is, it does not destroy the microscopic thin oxide surface film that provides corrosion resistance (except under unusually severe conditions not usually encountered in pickling). Since nitric acid oxidizes, it cannot dissolve and remove oxide scale from stainless steel when used alone or in solution.
Many equipment cleaning operations use citric acids, such as pharmaceutical processing equipment, whiskey storage tanks, steam generators, and nuclear reactors. The advantages of organic acids of this type include their ability to combine with a wide variety of other chemical compounds, as well as their ability to hold the iron in solution and to be handled safely.
5. CIP/SIP compatibility
In CIP systems, cleaning takes place without dismantling the system. CIP refers to all those mechanical and chemical systems that are necessary to prepare equipment for food processing, either after a processing run that has produced normal fouling or when switching a processing line from one recipe to another.
All Rheonics sensors are fully compatible with CIP/SIP systems. While ordering ensure the maximum temperature and pressure class is selected that satisfies both operational conditions as well as conditions during cleaning.
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