Outro Acidente Onshore

Senhores,

Este deve ser o 3º este ano que posto aqui, destes 2 foram nos EUA e um na Africa.

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January 28th, 2012

I've just received a report that Patterson Rig #491  drilling at Keene, North Dakota near Williston  had a boiler explode last night killing one and seriously injuring another.
The deceased worker identified to us only as "Rickey" was a married 38-year-old who had just broke out in August of 2011. The worker who pulled Rickey away from the exploded boiler is in the hospital with third degree burns.

Patterson Rig #491 is a top drive equipped 1400 hp rig listed with a CRG 200hp Boiler.

(CRG Boiler Diagram)

The last available rig report lists Patterson UTI Rig #491 drilling a horizontal well for Petrohunt LLC in North Dakota.
Patterson UTI could not be reached for comment


"It is law that you must check the water level in the boilers and dearator / feedwater tanks every 20 minutes, however checking the water every 10 to 15 minutes is much safer as it doesn’t take that long really for a steaming boiler to run low on water.  For the every day worker “running low on water” is the main reason for boiler explosions.  That is done by the main low water cut off and the aux. low water cut off failing to work or having the limit circuit jumpered out, therefore electrically removing it from the system.  The limit circuit contains the operating pressure control, manual reset high pressure control, and the low water cut off’s.  The main low water cut off and feedwater pump control is a float type that has a brass float that floats on the water that is in the bowl and when it drops to a lower level it turns the feedwater pump on.  If the water continues to drop it trips a switch shutting the gas /oil burner down.  If for some reason the main LWCO fails, there is always an aux. LWCO that is usually a probe that sticks down into the water and is powered.  If for whatever reason the water drops off the probe the electricity is no longer conducted to the aux. LWCO control and then the burner shuts down.  If both should fail then there is no low water protection. 
 
When the water gets too low in the boiler, the tubes that carry the hot flue gas no longer can transfer their heat to the water and consequently overheat and melt.  The big reason for boiler explosions from a boiler that is low on water like this is human error. Someone usually catches the boiler with no water in the water glass (the glass tube on the side of the float type LWCO) and starts water flowing into the boiler, which by then is overheated.  At that point when the tubes are red hot, even hot feedwater is too cold and causes a massive explosion.  The best thing to do when someone catches the boiler with no water in the glass (at that point no one knows what the actual water level is) is to shut the boiler down and let it cool, then have the boiler opened by a qualified boiler mechanic or technician and check the condition of the tube sheets and tubes.  Most likely the boiler will have to have the old tubes removed and new tubes put in. 
 
There are a variety of other reasons that the boiler could have exploded as well, including equipment failure such as weak welds, tube sheet failure, a crack in the boiler shell, or the feedwater tank could have run out of water, but 99% of the time it is low water.
 
The other type of explosion is called a fireside explosion, and they generally occur when the boiler lights off.  Sometimes there is delayed ignition, which occurs when the pilot or spark is present for ignition, and the burner programming control (which runs the burner sequence of operation) allows the main fuel valves to open in correct time, but the fuel doesn’t light off right away.  The combustion chamber fills up with fuel and air, then lights off, causing an explosion.  In a mild case it’s called a puffback, and the force usually goes out the stack, or can blow the stack off the boiler.  This usually happens if the fuel doesn’t light for 1-2 seconds.  In a more severe case, 3-4 second delayed ignition can blow the back door right off the boiler, taking out anyone or anything that happens to be behind the boiler.  (This happened to my father back in 1988, he lost an eye, his nose was taken almost all the way off, and he was in the hospital for several months – he is lucky to still be alive...and he’s still working as a boiler technician today.)  The programming control will shut the burner down immediately if it doesn’t sense main fuel ignition within 4 seconds tops.
 
Having discussed the types and reasons for boiler explosions, two things remain to be said.  One, it is very important that a boiler is torn down at least once a year, the waterside and fireside cleaned thoroughly, and inspected by a boiler inspector.  And two, the boilers out in the oil fields are boilers just like anywhere else, they need to have the water levels checked at least every 15 minutes by the motorhand or someone qualified to run / repair the boiler. (Even as a floorhand, I was the one who took care of our boiler because I was qualified.)  I know from experience on our rig, depending on what jobs were currently being done (tripping pipe, etc.) the boiler could not always be checked every time.  But is it worth the risk of lives???  Having come out of the boiler field...no it’s not.  It doesn’t matter what’s going on on the rig, check the boiler anyways.  The boiler is just as dangerous in its own way as the well is in its way.
Boilers need CLEAN water to run correctly, and there needs to be proper boiler water chemicals added also.  When rig boilers are hooked up, most of the time water from the rig tank is used and the condensate from the steam system is put back into the rig tank.  This is an absolute no no when it comes to good and safe boiler operating practices.  As I discussed earlier about the primary low water cut off (LWCO), I made mention about it being a float type with a bowl that is filled with water.  The water from the rig tank is generally filled with mud and other debris, and as the water is evaporated in the boiler, it leaves the mud to settle out in the bottom of the boiler and in the bowl of the LWCO.  If enough mud builds up in the bowl, it will not let the float drop enough to trip the boiler out on low water condition.  If more mud builds up, it then will not let the float drop enough to even turn on the feedwater pump, then allowing the boiler to run low on water.  As to why the aux. LWCO of on the Patterson-UTI rig 491 boiler didn’t work is still a mystery and may never be known.
 
When the boiler was fired up on our rig for the first time, I was off hitch.  When I arrived, the motorhand told us to blow the bottom blowdown on the boiler down once per tour, but not to touch the blowdown on the LWCO.  That was completely wrong as the bowl of the LWCO has to be blown down once or twice per tour as well to keep the float chamber free of mud, allowing the float to work correctly with a full range of motion.  In addition, the bottom blowdown (smaller boilers have a single blowdown in the back while bigger boilers have one in the front as well as the back) has to be blown down once per shift in a plant where clean water is used, but needs to be blown down at least 2 – 3 times per tour on rigs where muddy water, creek water, etc. is used.
 
When I first hooked up our boiler to the heating system, we used clean water and returned the condensate back to the feedwater tank on the boiler skid, so it was a closed loop system.  We got another pusher who was strictly old school and was not open to any new or proper ideas, and despite discussing proper boiler operations with him, he absolutely insisted that we use rig water, and that we return the condensate back to the rig tank.  He basically said use muddy water and screw the boiler chemicals.  In the spring when the boiler was sent back to the yard and opened up, it was so full of mud it was pathetic, and the tubes were so pitted that it needed a complete retubing – all that after half a heating season.  Needless to say this year we don’t have the boiler.
 
Looking back, I can see some very startling things.  A lot of these guys that are overseeing these boilers have never seen a boiler in their life, let alone run or repaired one.  And a lot of times they are not given all the information that they need to properly run or care for a boiler.  Consequently, most of these guys out there know just enough to be dangerous.  If whoever owns the boilers would do what they could to completely prepare their motorhands (or whoever oversees the boilers) for proper care and operation of the particular boiler they’re using, or hire a dedicated operator who knows what to do, and use clean water in a closed loop system and forget the muddy rig water, rig boilers would be a much, much safer operation."

There is one thing that should be done every tour, and that is checking the LWCO’s to make sure that they indeed work.  When you blow the bowl of the LWCO down to remove the mud, it is going to drive down the float and automatically kill the burner.  But say that there’s a little bit of corrosion in the bellows of the LWCO head that contains the float, what happens then? 

 

By blowing the LWCO down it drives the float down forcibly, but under normal slow dropping like it does when the water in the boiler drops normally, will the float actually drop or will it hang up??? Good question.

 

  That is where a “natural evaporation drop test” (NEDT) comes into play.  Shut the feedwater valve at the boiler so that no water can enter the boiler, and let the water drop naturally as the boiler steams.

 

  Boiler feedwater pumps are centrifugal pumps, so they can safely be deadheaded.  As the water level drops in the boiler, you will hear the feedwater pump start, but no water can enter the boiler.  As the water drops further, the boiler should shut down with roughly 1/2 inch of water still in the water glass.  Make a mark on the water glass at this point as this is the point where the burner shuts off. 

 

If there is corrosion in the bellows on the LWCO head, it will not allow the float to drop all the way down at natural evaporation speed, therefore not shutting the boiler off on low water.  at this point, just hope your aux. LWCO works. 

 

If the burner shuts down on low water, open the boiler feedwater valve and reset the manual reset aux LWCO control.  When the boiler fills sufficiently, it will restart automatically.  If the boiler does not shut off when the water level reaches the very bottom of the water glass, open the boiler feedwater valve, fill the boiler up with water to operating level, and notify your supervisor IMMEDIATELY.

 

Hope all this info helps someone out there to be safer, and perhaps fix unsafe operations.