ASME CSD-1 and probe style LWCO

[Jazzerman]

Anyone out there run into this before or offer their thoughts:
I designed a central steam boiler plant for a hospital - 150 psig relief valves. The boiler water level LWCO safeties are Warrick probe style conductivity sensors. Facility experiences frequent power bumps in incoming grid electricity, which cause the probe style LWCO's to trip. Since LWCO#2 (the lower one) is a manual reset as called for by code the brief interruption of power locks out the boiler until an operator can come in and do a hard reset. While it is recommended to have 24 hour supervision for this class of plant, it is not required by our state and thus the plant engineers only are on site two shifts during the week, less on weekends. Brief power outages knocking out steam plant is causing major grief.
ASME CSD-1 section CW110 (under general requirements for water level control for all boilers) state: "Probe type LWCO's- An open circuit failure, break or disconnect of electrical circuit causes shut down of the fuel supply".
In looking up the LWCO's that we have, Warrick model 26,

http://www.gemssensors.com/~/media/GemsNA/CatalogPages/series-26-low-water-cutoff-cat.ashx

I see that the model 26 is CSD-1 compliant and UL 353 listed. There is an optional feature for preventing nuisance trips due to power outages. Looks like just the ticket. Boiler mfr. however says changing to this option model will be non-compliant and will void warranty. I am going to call Warrick in the morning to see if the optional device is compliant, but I am looking for advice / input on this situation.

 

[Compositepro]

Put the boiler control circuits on a small UPS (uninterruptible power supply.

 

[hacksaw]

Most such controls are run from redundant power, in effect an industrial battery backup. Such systems are available, and depending on your need can be configued for redundant backup.

Short of lossing power for all prime movers, you want the emergence controls to remain powered otherwise you are flying blind.

You will also need emergency lighting.

Having said all that, most modern hospitals in have emergency power backup to avoid a complete blackout.

 

[Jazzerman]

Yes UPS or capacitor were my 1st thoughts. The LWCO is UL listed and I'd rather not change part and pieces in the mfg wiring of the boiler and control. So I was excited to find Warrick offers a power outage option that can be ordered on the same model 26 LWCO that is OEM installed on boiler, and the power outage feature will do exactly what I need: If probe is immersed when power is lost the control is de-energized then when power is restored the control circuit will re-energize. However loss of liquid will cause control to de-energize and remain so until liquid returns to probe and pushbutton is pressed.
That is exactly what I need. However blr mfr says this is not code compliant - would be for section IV boilers but not for section I. I think it may come down to interpretation of CSD-1, and how they treat probe style LWCO. Regardless, if the OEM mfr says is it not compliant, I probably need a different solution. May need to switch to a mechanical float, where switch only breaks when water is low, not when water is low or power goes out.

 

[GenB]

Warwick 26/with power outage is acceptable for section I, I use them lot, other complications not to mention here. With a power backup is a good combination. When power goes out don't forget feedwater and burner restart can be dangerous and that is why some Mfrs are reluctant to accept auto resets without operator present.

General Blr. CA,USA

 

[Jazzerman]

Thanks for weighing in GenB. Point taken on getting the operator in front of the boiler after a power loss. They don't do it now and this is exactly what they are trying to avoid. They want the plant to come back on it's own. In out state it is recommended but not required to man the plant 24/7.

Does ASME pressure vessel code talk about water level controls? I have read through CSD-1 and have found the following: Under section CG-610 LOCKOUT: "Safety controls that can electronically reset without local manual intervention, such as when power or control input to the device is interrupted and then restored, shall not be permitted." To me this is expressly denying the Power Outage optional feature of the Warrick 26 (or other conductivity style LWCO). I am thinking the thing to do is go simple and swap the Warrick 26 manual reset LWCO to a float style such as the McDonnell Miller 93. It simply avoids the issue altogether - as the switch breaks only when water level is actually low, not when water is low or when power is lost.

 

[GenB]

They are exact same. The power outage on the float is built in the controller since the float never breaks the switch. It's a matter of interpretation of the Code. And you have to consult your state, Jurisdiction because they may interpret it different and you may not be able to defend the issue.

General Blr. CA,USA

 

[Jazzerman]

I described the situation to the state boiler inspector (MT). This specific question had not come up before. After doing some research his answer was that the Warrick 26 with the power outage feature would not meet the ASME CSD-1 code. But that a float style control would be acceptable. So I have my path forward - change order to swap out the manual reset LWCO. Certainly a nuance of the boiler control trim that I was not aware of and turned out to be quite important on this project.

 

[GenB]

I did mention the auto reset of the warrick 26 and floats are exact same and it is a CSD-1 compliant. The float will re-start the boiler in the same manner w/o operator present. It just that technology is advanced and hard to understand. I hope the ASME will answer positively. Certainly Warrick should address the issue with the ASME CSD.1 to clear all doubts.

General Blr. CA,USA