Ammonia Refrigeration System in the Food Industry: Where to Test, What to Look For

All piping in an ammonia refrigeration system—including long and short runs, vertical, nested, and suspended piping—is subject to degradation and should be tested at the following areas:

• Periodically along long runs of pipe;
• The intersection of the pipe segment and major pieces of equipment;
• Before and after direction changes (e.g., elbows, tees, reducers);
• Wall and roof penetrations;
• Insulation terminations (e.g., valve groups, end caps);
• Low or “sagging” areas of a line segment; and
• Areas of concern or those identified as suspect during a visual inspection.

For all pressure vessels that are at least 10 years old and/or show external evidence of corrosion or degradation, testing should be performed on areas where water is most likely to infiltrate and corrode the shell or heads. Uninsulated vessels should be tested on areas where the most corrosive activity is present.

When possible, owners should employ NDT that does not require the removal of secure, intact jacketing and insulation. Cutting holes in or stripping the insulation breaches the vapor barrier and threatens the mechanical integrity of the insulated component.

Corrosion under insulation (CUI), or pipe and vessel external corrosion, is the primary damage mechanism that affects the integrity of ammonia piping and vessels. Moisture enters the insulation and becomes trapped against the pipe, vessel wall, or valve, and corrosion forms on the surface wall. If unaddressed, the corrosion will persist over time, eating away at the exterior wall and thinning the metal to the point of failure. Due to the variables present, progression time from moisture entering the insulation to the point of failure varies. Using testing to obtain accurate wall thickness values for your piping and vessels is critical.

Ensure that the chosen NDT technique uses technology that does not require direct contact with the component wall (specifically piping and vessels). Or, if contact is necessary, confirm that valid thickness readings are collected by using suitable couplants that will not freeze.

Damaged insulation jacketing, biological growth on the jacketing or insulation, and excessive ice build-up are all visual indications that moisture is or is likely to be trapped in the insulation; however, not all trapped moisture is revealed visually. On average, 30% of a system is compromised by moisture trapped in insulation, and the majority is not evident visually.

Testing for ammonia refrigeration piping and vessels, at a minimum, must be capable of collecting and reporting on the following data points at the aforementioned areas on insulated and uninsulated piping:

1. Location and volume measure of moisture in insulation;
2. Location and measurement of corrosion; and
3. Pipe wall thickness (on the top and bottom of the pipe).

Additional information can be captured during testing that is helpful with decision making and PSM compliance. Some testing can (but is not required to) locate and measure pipe size and schedule, welds, blockage, liquid levels, and other components, including valves and reducers.

A facility’s entire system should be tested every five years. Many companies with larger systems test different sections over the course of five years, resulting in a comprehensive test for each cycle. Exceptions to this rule occur in the event of a release, when areas of the system are rapidly degrading and it’s determined that testing should be employed more frequently for monitoring, or on areas that have been flagged as suspect and whose state cannot be determined.

Implementing regular testing, adopting the minimum requirements in ANSI/IIAR 6-2019, and establishing corporate-specific directives in PSM programs, especially in today’s landscape, are paramount.

Compliance and Safety

EPA’s Risk Management Plan Rule (40 CFR 68, defined by Section 112(r) of the Clean Air Act Amendments) adopted the OSHA PSM standard as its prevention program for processes in Program [Level] 3. Compliance and safety continue to be high priorities for EPA. In 2016, the agency announced a series of national enforcement initiatives focused on improving safety in a variety of high hazard industries. Among these initiatives was an effort entitled, “Reducing Accidental Releases at Industrial and Chemical Facilities,” which has subsequently been renamed a National Compliance Initiative (NCI).