Low pressure steam boiler with 25psi on the steam gage

EBEBRATT-Ed

I usually install most of the time but I'm between installs now so I am helping out on service until the schools get out next week.

So, at 2pm yesterday I go on a call a Burnham steel boiler 2,500,000 btu low pressure steam with a Webster modulating gas burner. The customer complained of a lockout on MFF. First time at this account.The burner was running when I got their maintaining 10psi steam and modulating the flame.

So I put my analyzer on which had a low battery and some other issues (probably because I haven't used it in a while), checking gas pressures and adjusting the burner (low fire too small and unstable). High fire is fine, low fire still not happy with that and checking the flame signal when I came out to the front of the boiler and see their is now 25psi on the pressure gage. Now I quickly become less concerned with the burner issue.

Kind of stunned me for a second as I reached for the off switch.

No discharge from the safety valve, I checked the L404A operating pressure control and The L404E manual reset high limit (on separate pigtails) and the mercury in both controls was no ware near tripping.

I decided the steam gage must be bad so I went out and got a gage on my truck. A pet cock on the steam trim wouldn't open (didn't want to snap it) but their was a petcock on the gage glass blow down so I opened it to make sure it was clear and put the gage on.

It read 20 psi within 1 psi of the boiler gage. The steam pressure had dropped 5psi since I shut it off.

Stood their for a few not believing what I was seeing. 20 psi on the boiler, 2 gages agreeing, no safety valve discharge and 2 pressure controls on 2 pigtails not moving??

I notice the pressure controls were mounted out of level a fair amount so I fixed that thinking that would solve the pressure control issue.....nope.

Customer didn't want to shut down, process load but I insisted so I had to baby sit it a while then shut it down at 3;30 when most of their employees leave and proceded to dump some steam.

I took off both pressure controls and they were very clean on the inside. Took off both pigtails (steel) both plugged up solid couldn't blow any air through. I took the safety valve off and found the seat frozen to the disk, no sign of any corrosion or gunk. All boiler connections to the pressure controls and safety valve were clear.

No way to get to the supply house before they closed so I got the safety valve to open with a hammer and a screwdriver. I reinstalled the pressure controls with 1/4" nipples and started the burner. Watched the burner cycle on pressure 3 times. The safety valve was free and was leaking some steam at 10 psi and I could manually open it so I let it run.

I returned first thing this morning and put new brass pigtails under the pressure controls and checked their operation. I also replaced the safety valve. The boiler is due for it's summer shutdown and inspection so we will see what it looks like then. Maybe a water treatment issue??

Just a few more gray hairs that I don't need. I think that boiler would have made the local news this morning after it exited through the roof. I still find it hard to believe.

Steamhead

They were extremely lucky, not only because the boiler didn't explode, but because they have you working on it now. Good job!

I'm assuming if there was no way to get the Pressuretrols and safety valve to work, that you would have pointed out the boiler's maximum allowable working pressure and then shut them down- process be damned.

Jamie Hall

That's just real scary...

RomanP

I saw the boiler explode in the news couple of years ago. Pretty scary I must say. Took the roof off commercial building with debris flying couple blocks away. Looks like a missile strike lol

The first plumbing company I started to work for, used to service few factories with high-pressure steam boilers. Walking around those monsters made me feel a bit uncomfortable lol

EBEBRATT-Ed

@Steamhead

Too much risk, no way I could let that thing run.

Never mind a potential boiler explosion my real problem is I wouldn't have been able to sleep anyhow.

My next step would have been to make some calls and open up a supply house which I didn't want to do.

DanHolohan

Gosh.

jumper

With all the redundant safeties required nowadays,why aren't there any based on temperature? Also rupture discs seem fool proof. You'd suppose that B&M Insurance would require them.

Steamhead

@jumper , good point. I recall seeing some illustrations of temperature-based steam limit controls in an old Audel oil burner book. Now I just have to find them................

According to an online calculator, the saturated steam temperature at 15 PSIG is 249.7° F. So, theoretically, an aquastat set at 245° should shut the burner down if it sees that high a temperature. But the question would be, would the Code authorities accept it?

Also, you must be thinking of fusible plugs rather than rupture discs. These were found in steel boilers such as were used in steam locomotives, located in the crown sheet so they would melt if the water got too low and the crown sheet overheated. IIRC, these were sized to relieve steam pressure at a controlled rate- if you let the pressure drop too fast, it could cause the remaining water to flash to steam, resulting in an explosion.

EBEBRATT-Ed

Many times you see 15 psi safety valves weep if you operate close to 15 psi. I always try to keep the pressure under 12 but on process jobs they want it as high as possible. Their is a certain % of safety valve setting that you can run up to but I cant remember what it is. Had a salesmen sell a 15psi boiler to a customer and he told them they could run at 15. Should have been a HP boiler on that job but they wouldn't want to pay a licensed steam engineer that the Republic of Korea ...I mean Massachusetts requires on anything over 15psi

The safety valve was stuck shut but a hammer and a screwdriver got it loosened up. I replaced it anyhow.

Funny thing is it looked pretty good no real evidence of corrosion or any weeping or leakage. I am thinking now I should have added a check valve or a vacuum breaker to the boiler

jumper

Fusible plugs is an even better idea than rupture disc.

I believe the code test is cold static pressure 50% above the boiler's rating. So a low pressure boiler is supposed to be able to take 22 psig cold without harm. Note the word supposed.

Used to call low pressure "strictly atmospheric" which to me means not much above zero. For 15 psig it makes more sense to buy a used pressure boiler and get it derated to no pressure.

EBEBRATT-Ed

Rupture disks are use on chillers with low pressure refrigerants. Don't think they are used on boilers

gennady

I used to work at power plant in USSR.
3000+ psi. Each boilers had few elevators, boilers 10 stories high. Had no uncomfortable feelings.
Pop safety valve setting must be no less than 1.25 of working steam pressure and no more than 15 psi to qualify for low steam pressure.