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Valve Inspection & Corrosion Mitigation

Posted by ORR Protection on Oct 9, 2020 10:37:13 AM

During the MCFP Virtual Conference series, expert Lee Kaiser, covers valve inspection & corrosion mitigation for both wet and dry systems. In the video below, watch as Lee dives in-depth on what is required for inspection and mitigation.  

Video Transcript:

This brings us to talk about valves.  There are a number of valves in Chapter 13 of NFPA 25 to talk about but we're just going to highlight a couple of them.  Control valves, alarm check valves and pre-action valves.  Control valves, a very common valve, are just manual valves to shut off or open up for flow within the system, and they need to be inspected monthly.  We'll see this monthly inspection as a recurring theme.  Are they in the correct position?  If they're supposed to be open, are they open?  If they're supposed to be closed, are they closed?  If there's a tamper switch, is it present?  If there's no tamper switch, then it has to be locked in position. 

If you zoom in on that picture of a sprinkler system control valve, it has both an electronic tamper switch and it is locked in position.  So it shows you both items.  As a minimum code requirement, you can have one or the other.  I know there are some jurisdictions that require both.  Is it accessible? Is the valve leaking and does it have proper signage?  Each control valve should have a little sign on it showing its indication what it's supposed to do when there's a fire.  For tamper switches, there's a testing procedure for those.  They need to be tested semiannually.  And as an item of maintenance on a control valve, it needs to be exercised once a year.  That means each year, it needs to be fully opened and fully closed so we can exercise that valve and know that we could use it when we need it during a fire to shut off the sprinkler flow. 

Alarm check valves.  We don't use a lot of alarm check valves in systems because we moved to a lot of backflow preventers as our check valve means.  But for the buildings to still have them, this is how they get inspected.  A monthly inspection looking for the pressure gauge readings, looking for any trim valves, if they're in their appropriate position, and that they're not leaking.  Every 5 years we need to open the valve body up and do an internal inspection of that alarm check valve. We hope that we don't see a picture like that's on this lower right where there's a bunch of corrosion-related debris inside of that system and it would need to get cleaned up and again, this would be a place where we'd reinforce.  We need to maintain that valve in accordance with the manufacturer's instructions to do that.

A new valve to talk about is a pre-action valve.  Pre‑action systems are a type of dry sprinkler system where we don't have water resting in the pipes.  We have water coming into this valve and it's held closed.  Downstream of this we have air in the pipes, usually compressed air, at a given pressure so we can supervise that valve.  That valve will be either held closed by that air pressure or in a dry-type system. In a pre-action system we've got other things that hold that valve closed, but it's there to supervise when we have a sprinkler head fuse when pressure drops and then we know to do things with that valve to allow the water to flow.

"You could use nitrogen as well."

That's right. We're going to get to that. Some of these systems do use nitrogen.  An internal inspection is required on a monthly basis. Something new is that we need to inspect the electrical component. Pre-action systems are more complicated than other dry‑type valves. There are electronic components on it such as the releasing solenoid, supervisor air pressure switch, pressure-type flow switch and a normal tamper switch on the incoming water supply. We need to do an internal inspection on this valve on a yearly basis. Now we're doing it on a yearly basis, and it's recommended to do it during the trip testing.

So, what's trip testing?  Trip testing is an operational test where we walk through the sequence of that valve to make sure it will operate when there's a fire in the space.  It's a more complicated valve, combining mechanical components and electronic components and there's two varieties of trip testing that occurs.  There's the partial flow trip test which needs to happen every year, and then the full flow trip test, which is a less frequent, every 3‑year activity.  Partial flow trip testing, we step through the sequence of the valve and we just allow a little bit of water to flow through the valve.  We don't want to fill the system with water.  That's not the intent during partial flow trip testing, but during full flow trip testing, we do want to fill the whole system with water, and as I mentioned before, we install the inspector's test connection on a dry pipe system at the end of the system as far away from the valve as we can get.

We want to flow water all throughout the system from the pre-action valve to that inspector's test connection valve at the end so that we can reveal any corrosion in that piping.  If we see that there's corrosion in the pipes or corrosive-related debris that's discharged in the drain water, then that's going to trigger a Chapter 14 internal obstruction investigation, where we're going to try and see how bad is the corrosion? What can we do with it to clean it up or try to mitigate it? 

During any of these trip tests we want to try and drain the system after we do the test.  We want to try and minimize the water in the system.  During trip testing we create the perfect environment to cause corrosion in those pipes. It's just what we have to do to make sure they work. Anytime we have unprotected steel pipe, water and oxygen that's present in the air we create the perfect conditions for corrosion inside the pipe. We're seeing this as an issue in today's installations because we choose to save money and install thin wall piping systems such as Schedule 10.  There's always been corrosion in our dry pipe systems.  We just didn't know about it because Schedule 40 systems didn't necessarily reveal it in pinhole leaks as fast as Schedule 10 systems do, and so those Schedule 10 pipes, the same amount of corrosion inside of the pipes can more quickly establish a pinhole leak and we'll see that as an early system failure.

We can stop corrosion by applying compressed nitrogen to those systems instead of compressed air. Nitrogen breaks that corrosion chemical reaction and stops basically the rust reaction so that they don't corrode.  Once we get rid of the oxygen that's present and replace it with compressed nitrogen, we can stop that, and one of the ways to do that was with a nitrogen generator.  Another way is with a bottle gas system. 

Either way, for existing dry pipe systems that have corrosion problems or pinhole leaks, one of the ways to fix that is to evaluate the degree of the corrosion problem and replace the sections of the pipe that have been damaged or patched, whatever we need to do, and then install a nitrogen generator or other nitrogen source to prevent further corrosion.  The specifiers in this room need to know for their new dry type systems that they're specifying to just think about specifying a nitrogen system from the get-go to prevent corrosion and extend the life of that system as it gets installed.

The next thing on this side is wet type systems.  How do we control corrosion on wet systems?  Well here's the difference between a wet pipe system and a dry pipe system.  We have pinhole leaks at the top of wet pipe system where we have trapped air and we have that air‑water interface.  We have pinhole leaks in a dry-type system at the bottom of the system where it's easier to get to because that's where water left over after our testing.

The MP13 Committee has established that we have leaks in wet pipe systems too, so they've added a new requirement to have air vents in new installations. One way you can go beyond that and exceed the minimum code is to install your wet pipe systems with wet pipe nitrogen inerting systems.  The picture here at the bottom shows that in this wet system, before they fill the system with water, they'll connect a cylinder of nitrogen and they'll pressurize it up to 40 psi and then drop the pressure back down to 0.  They'll re‑pressurize it to 40 psi and drop it back down to 0.  It takes three cycles before the pipes from the mains clear all the way out to the ends of the branches and filled with nitrogen. Then they disconnect that cylinder and allow the system to fill up with water so that any trapped pockets of air in the system are now really trapped pockets of nitrogen. 

Our experience with that is that we can stop system leaks by doing that.  A problem of systems that have a lot of air trapped can benefit by this and can stop the leakage problems that are in existing systems.  If you want to know any more about that, Chris and Dan can talk to you about wet pipe nitrogen inerting if you've got any existing systems where that's a problem.

The last thing on sprinkler systems is the fire department connections.  I include this for the guys with patches and the badges on their shirts.  The fire department connections are where the fire guys pull up with their pumper truck, and connect their hoses to support the flow and the pressure of the system if there is a fire and the sprinkler system's operating. The fire department connection's on the outside of the building needs quarterly inspections making sure it is visible and accessible, and that couplings or swivels are undamaged.  This picture shows one of the swivels is knocked off of that device.  Also look for any obstructions inside of that.  This one has trash inside of it.  It's not going to have that if the caps and plugs are in place.  It also has a number of other things that need to be there that we need to inspect for.

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