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January 9, 2020

Importance of a Steam System Warm-up Valve

STEAM SYSTEM WARMUP VALVES

My name is Kelly Paffel. I’m with Inveno Engineering located in Tampa, Florida. We’re a domestic and international firm, specifically for steam and condensate systems in industrial plants. Today I want to talk about steam warm up valve system for a safe, reliable steam system operation. One of the things in a steam system, specifically at the warm up, we have to have a correct warm up valve installed in the system. The importance of a steam warm up valve, it’s really a central part of the steam system. So at the initial startup of the system and a warm up of the system, the highest kind of condensation or liquid or the condensate will occur. We want this to occur over a period of time. Also, the thermal expansion of the steam system will occur at the startup. Therefore, we want to be sure we have a controlled startup of the steam system.

But to do this, we need a predetermined timeframe for the warm up. A rule thumb is one PSI per minute or longer. So if it’s a 60 PSI system would take 60 minutes to warm up, but more time is always better. A slow ramp-up time is desired to temperature to steam temperature and pressure, so we’re controlling that warm up period with a small valve and a bypass around our main isolation valve. The thing is you cannot control the warmup with a six- or eight-inch valve. Therefore, we need a warm up valve in a bypass loop to control the warm up period.

Isolation valves are three inch and larger, so people always ask, “What’s the application?” If I have an isolation valve at three inch or larger or pressure reducing valve that’s three inch or larger, then I’m going to have a warm up valve so I can control the warm up period. This one example that you’re looking at as a steam control valve. I mean, the thing with that is that if I take this and try to use a four-inch control valve to warm up the system slowly, it’s not going to occur. So, therefore, we want the warm up valve to be put into operation. We also do the warm up valve for certain types of process application. So just not limited to a pressure-reducing valve or an isolation valve. Now, a lack of proper steam system warm up valves, the negative effects in the system can be a safety issue.

You know, you open the valve too fast and send a slug of condensate down the line. You can generate severe water hammer. Also, condensate passing at high volumes through elbows can cause line erosion. Of course, the water hammer will cause premature component failures in the system. High velocities will cause erosion on the different components of the steam system. So there’s a lot of negative effects and a lot of them are safety issues. It was really critical that we have warm up valves put into the system.

Now, typically older technology we use for isolation valve installation is a common gate valve. And the inlets to the gate valve, we classify that as P1, down here is P1. So you have pressure forces here against this side of the gate forces that gate up against the seating surface. And P2 down here, zero pressure. Those forces up against that gate, pushing that gate against the seating surface you’re going to have, if you don’t equalize that pressure, you’re really going to have to use force up here to open that gate valve up.

Older technology isolation valves, using force on any gate valve is very unsafe, because the manufacturer of valves here do not design this bonnet for the external forces. It doesn’t design putting a huge cheater bar or a handmade fork mechanism like this here or a pipe wrench and then two people trying to force this valve off of it, the valves seem to open up. If you’re using external forces, you can, and it happens, break the bond of the valve and now you’re releasing all that pressure to atmosphere and the steam is going to expand 1600 times and the forces are pretty dramatic. And you do not want to be there. There’s also people out there that make these type of wrenches here for opening the valve. They’re not needed if you do it correctly, if the system is installed correctly, you do not need to put the forces to it. And we’ll talk about that.

Now, the newer technologies is using bar or butterfly isolation valves. We’d call that newer technology because there’s not been any great revolution in gate valve since 1941 and we just use ball butterfly because of the seating and everything else. And the technology is accelerated. But using bar or butterfly or quarter turn valves, so it is essential that we do have warm up valves installed into the system. Now, the thing is, is this is this happens to be a typical installation of a warm up valve. And as I said, you know the warm up valve can be down here, can be half inch, three quarter inch or one inch, and it can be a single valve or it can be a two valves. It depends on how the size of the steam line is and how much line we have to warm up. So it depends on the length and the diameter of the steam line.

But typically a one valve arrangement can be easily accomplished. What we’re trying to do is get pressure onto the backside of this valve, so the gate will come into the neutral position. You’d be able to open the gate valve without using any external force? Now, selecting a warm up valve, number one, a needle valve is preferred for throttling steam because we can control that. The second choice is a ball valve that can be used in the open position, so besides a ball valve that we can just open up and allow it to flow the steam down the system. Now putting in a warm up valve, as I said before, one or two valves can be used and typically we put it into this piping configuration. So we really are using this valve here for the warm up, but during normal operation we can shut these valves and this here is to make sure the valves are not leaking through.

The other thing is that we always want to increase this size of this pipe downstream here by one pipe diameter. Allow the steam to flow out, increase in volume without having high velocity causing premature failure of the system. This just happens to be a standard application for a warm up valve put into the system and your drip pocket ahead of the warm up valve or isolation valve is a nice feature to have. Every installation we do, we put in a drip pocket here to make sure that no condensate’s going to pass through the valve causing premature failure and we get longevity.

The key to it is that you do not have to use external force. The isolation valve will come into the neutral position. You’d be able to open it up. Or the butterfly valve, you’ll have pressure on both sides and then you can open the valve up safely. And the critical thing that this is safely. This is our contact information and our short-term impacts, our steam system assessments, steam system engineering, steam balancing, performance, and we do training long-term impacts. We do great upgrades, process change and improve reliability and safety. Thank you for your time. Have a great day.