From fertilizer and petroleum to textiles and plastics, production of vital commodities around the world relies on the use of anhydrous ammonia. Operators of chemical plants and petroleum refineries are well acquainted with both the handling hazards of the compound and the precision measurement needed to ensure its water content remains in the narrow range of 0.2% and 0.5%. With product quality and the risk of corrosion at stake, regular and reliable ammonia testing a must.
Sampling ammonia is typically neither simple nor quick. Ammonia vapors are highly toxic, dangerous to both touch and inhale, and can cause burns to the skin, eyes and lungs. Anyone gathering a sample using traditional sampling methods needs a full set of personal protective equipment (PPE): a chemical suit, goggles, a respirator and gloves. The process of collecting and testing the sample is also time-consuming and requires demanding precision to deliver accurate results.
Taken together, these factors mean that traditional methods of ammonia sampling are not only hazardous, but have greater potential to provide inaccurate data and significantly hurt efficiency. One way of addressing all these impacts is to implement a sampling system that has been specifically engineered for ammonia testing.
Safely and accurately sampling anhydrous ammonia can be a time-consuming challenge
Challenges of traditional sampling
It is critical for fluid-system operators to know exactly how much water content is in the anhydrous ammonia used in their processes. Why? The compound’s harsh nature can increase the chances of stress corrosion cracking in system components like storage tanks if its water concentration is below 0.2%. This type of cracking is difficult to detect as it’s happening, since it can destroy a component at stress levels below an alloy’s yield strength. A resulting failure can occur without warning and release the highly toxic ammonia. Recall the PPE and the need for spillage prevention previously mentioned — anhydrous ammonia exposure is very dangerous to workers and the environment.
At the other end of the water concentration range, any more than 0.5% water is excessive and dilutes the value of the ammonia to customers. That small window between 0.2% and 0.5% is where refineries and chemical plants need their anhydrous ammonia’s water content, so the need for quick, reliable, and safe testing is clear.
Ammonia sampling and testing is usually done with the CGA G-2.2 method developed by the Compressed Gas Association, Inc.: A 100 mL sample of liquid ammonia is dispensed from the fluid system and then allowed to evaporate. The residual water from the evaporated sample provides a means to measure the ammonia’s water content. It is a relatively straightforward system, but there are variables which can compromise its accuracy.
For one thing, anhydrous ammonia is cold: It boils at –28°F (–33°C), which means it begins to boil and evaporate as soon as the sample hits the warm glass container. This makes it difficult to fill tubes precisely to the graduation line, and as we’ve noted, accuracy is paramount. Similarly, inconsistent rates of the ammonia sample heating up and evaporating can lead to inconsistent sample results. Additionally, if the sampling tube and transport line aren’t flushed properly, residue can get into subsequent samples and lead to data that isn’t representative of the actual water concentration.
It’s challenging to perform this manually with the precision and safety needed, and even then, manual sampling procedures often require up to 8 hours before the water content measurement can be taken.
What distinguishes a better ammonia sampling system?
One route to safer and more reliable ammonia sampling is to incorporate a pre-engineered grab sampling system. These systems help expedite the sampling process and enhance operational consistency, and can be configured to meet a wide range of industrial fluid and specific application needs. For example, a pre-engineered system designed for ammonia sampling would ideally minimize operator exposure to liquid and vaporizing ammonia while also reducing the possibility of introducing operational errors or inaccurate measurements.
For instance, a sampling system with closed-sample fixtures reduces the need for excessive PPE precautions, since it limits the possibility for operator exposure and environmental impact. And if these closed fixtures are made of glass, the operator can also easily monitor the conditions within.