#140 – Corrosion Management for Dry Sprinkler Systems / Preaction Systems

By Rob Stewart and Mary Raines

Addressing corrosion issues in dry systems is important and takes time.

Not approaching these issues correctly will result in you providing incomplete and ineffective servicing.

Knowing how to investigate these issues and how NFPA 25 helps you as a Fire Sprinkler Professional will result in you providing better service for your customer.

Have you seen pin hole leaks in a dry system? How about “sludge” sitting in the bottom of the pipe, or barnacles on the inside of the pipe?

The perspective from a contractor, inspector or tech is going to be different than that of a maintenance person or building owner, which for them is more of a maintenance headache or unwanted problem. Their solution: get it fixed and move on. But as the professional you should be asking the question: why is this happening to the system? Once the why is discovered, the how can effectively be addressed.

How does the NFPA 25 help you as a field worker?

NFPA 25 (2017) Section 14.3 addresses many issues you may run into when inspecting the dry systems.

For an example of a pinhole leak in the dry system, use the NFPA 25 to find the referenced section for this issue: NFPA 25 2017 Section 14.3.1 An obstruction investigation shall be conducted for system or yard main piping wherever any of the following conditions exist. All issues listed – NFPA 25 2017 Section 14.3.1 (1) – (15). Condition #14 is a pinhole leak.

According to this section the word shall indicates a mandatory requirement (per NFPA 25 2017 Section 3.2.4) which requires you to perform an obstruction investigation. An internal investigation will provide a better indication of why the pinhole leak has occurred. The investigation would start with evaluating the system at specific points, per NFPA 25 2017 Section (System Valve, Riser, Cross Main and Branch-line), which provides insight as to what is going on in the system.

Example: The branch-line is clean, the valve looks good and the riser is clean, but the cross main where pinhole repair was performed has a lot of corrosion or build up.

What are some questions to ask yourself?
  1. Is this cross main properly pitched for drainage?
  2. If not, are the drum drips being properly drained?
  3. Has the maintenance team been trained in draining drum drips without tripping the system?
  4. If there are no drum drips in this area, where can a drum drip be installed, so that the trapped water can be drained out?

By asking such questions you can better grasp what is happening with that dry sprinkler system. Remember each sprinkler system is unique, and it now becomes your challenge to discover what the underlying issues are in order to better help your customer.

When looking at Dry Systems, you know to perform a full trip test every 3 years. What else are you supposed to do every 3 years?

NFPA 25 2017 Section requires dry pipe systems to be tested once every 3 years for gas leakage, with one of these test methods:
  1. A two-hour gas (air or nitrogen) pressure test at 40 psi, with no more than 3 psi system loss permitted during the test. Address gas leaks greater than 3 psi.
  2. At normal system pressure, turn off the gas source (shop air or nitrogen supply, compressor) for 4 hours. Address gas leaks if the low-pressure alarm activates during this 4-hour period.

There is great value to test a Dry System for leakage every 3 years. However, not many pay attention to these systems. As a professional you are testing them on annual basis (maybe more depending on the customer), and you are inspecting/testing/maintaining their overall functionality. In reality, you don’t really know how tight the system is – you probably don’t even know how often the air compressor is running unless it becomes a nuisance to someone on that site. So, every 3 years you are to test for leakage. This allows you the opportunity to see if this system has any issues to be addressed.

To get the acceptance test signed-off after a Dry System is installed, you need to perform a 200lb / 2-hour hydrostatic test along with an air test (24-hour 40 psi test with an allowance 1.5 pressure loss this time). When the system was installed, it was tight – no leaks. But as with Dry Systems over time, they begin to leak. In many cases the air compressor keeps these leaks hidden, and as seen in NFPA 25, a certain amount of leakage is acceptable.

The process of following the requirements of NFPA 25 causes you to search not only the why of a Dry System issue, but to find how to resolve it. This standard is an essential resource to help you determine the health of a Dry System (or any other part of a sprinkler system). This gives you an opportunity to keep ahead and avoid bigger issues that could occur in the future.