Thermal shock. Is it real or theoretical?

JohnNY

I was told there is not a single documented case of a boiler cracking because someone added cold water to it while it was hot.
Does anyone know if that's true?

DanHolohan

https://www.nationalboard.org/index.aspx?pageID=164&ID=232

https://claritywatertech.com/dont-let-thermal-shock-harm-your-steam-boiler/

JakeCK

I just read something on pmengineer about a case where a new boiler was trashed by cold water from a zone that had been off for an extended time. I believe it was a church and the zone was for an area that was seldomly used. But that is a whole zone worth of cold water slugging the boiler, and who knows if any other zones were running at that moment to temper the water before it hit the exchanger. Adding cold make up water to a hot boiler... I'd imagine it depends on how much.

retiredguy

Before I retired in 2007 I worked for the biggest H B Smith distributor/dealer in Pittsburgh, Pa. We were supplying the series #28 boilers in new jobs and for replacements in forced hot water heating systems. Most of these boilers were installed in schools or commercial buildings. Many of the boilers would crack numerous rear sections throughout the heating season. We were able to determine that the cracked sections were being used on heating systems that utilized a night set back temperature. Boiler sections rarely cracked on heating systems that did not utilize a night set back temperature. I suggested to the owner, my boss, that we should install a run around pump to see if this would cure the problem. The first school to get outfitted with this pump was a Southmoreland school building in Alverton, Pa. We installed a B&G series 100 pump using 2" copper tubing after steel couplings were welded into the supply and return piping. The pump ran 24/7 during the heating season. After the pump was installed, no more sections cracked on this boiler. This "run around" pump system became standard equipment on any H B Smith series 19 or 28 boiler that we installed. On larger boilers larger pumps were used. The engineering department determined the size of the pump. This building has since been torn down.

Hope this sheds some light on the question.

STEAM DOCTOR

Had one residential customer. Came down one morning because no heat. Saw boiler was cherry red. Figuring correctly that boiler was out of water, he manually added cold water. Heard the crack of a lifetime. 

DanHolohan

@retiredguy, that was a very elegant solution!

JUGHNE

Perhaps no documation because few are going to admit doing what Steamdoctor's customer did.
The guy was lucky to have heard the crack and still be alive.

sunlight33

Heard the crack of boiler or the crack of his life?

JakeCK

STEAM DOCTOR said:

Had one residential customer. Came down one morning because no heat. Saw boiler was cherry red. Figuring correctly that boiler was out of water, he manually added cold water. Heard the crack of a lifetime. 

It's funny but man just thinking about that actually happening scares me. 

Fundamental lack of understanding of material sciences. 

Jamie Hall

Problem is... too many variables. I don't think there's much question that a rapid cooling (or heating) can, in some circumstances, cause cracking or other failures. But -- there are just too many things which can determine what the stresses are that might be set up, and how the materials will react to them.

Not that in a lab. type setting the phenomenon is all that hard to study -- and even less so now that sophisticated finite element modelling is available.

But just consider a few of the variables. To start with, the material. What alloy is it? Has it been previously heat treated? Are there microcracks or stress corrosion cracks or hydrogen embrittlement problems? More fundamentally what is its brittle/ductile transition temperature? Yield strength? Tensile strength? Then the part. What is its geometry? Dimensions? Uniform or stress risers? Where? What is the temperature distribution? What external forces are on it and how is the stress from those forces distributed in it? Then what is the thermal shock? Relative temperature? Heat capacity? Power available (related to flow and heat capacity)? Areal distribution (how big a jet)? Overall immersion (part dunked in cold water vs. hose sprayed on centre of flat piece)?

And those are just the starters...

And then you have the question of a boiler failing not from a thermal shock by itself, but from a related cause: for example, a red hot boiler with high heat capacity being hit with cold water and inadequate pressure relief. Is this a steam explosion? Is this a thermal shock explosion?

JakeCK

Not boiler related but years back while cruising down a rural highway a nice sized rock from a passing truck put a chip in my windshield. Not knowing at the time I could get the chip repaired I just left it. Come the first really cold winter night I had the heat blasting on defrost and I watched a crack grow from that chip clear across the windshield. I watched it thinking am I about to die from an exploding window? Lol

MaxMercy

I wonder if the new low volume boilers are more prone to this. I worry a bit about my hydro-air system as it has an air handler above the insulation line in my attic. There has to be a fairly good slug of cold water hitting the boiler when the circ starts. My mom's boiler is 50 years old and holds a lot more water than my new boiler does.

My plan this spring is to encapsulate the attic.

hot_rod

MaxMercy said:

I wonder if the new low volume boilers are more prone to this. I worry a bit about my hydro-air system as it has an air handler above the insulation line in my attic. There has to be a fairly good slug of cold water hitting the boiler when the circ starts. My mom's boiler is 50 years old and holds a lot more water than my new boiler does.

My plan this spring is to encapsulate the attic.

Good point, and the thickness of the cast seems to be going down in new boilers.

cross_skier

Even in a 100 year old boiler in a property I own the boiler rotted out in the location where the cold water was connected directly to the boiler.  Maybe not thermal shock but I took note and piped my water feed to a location in the return a long distance from the boiler.

The Steam Whisperer

I believe its very real problem. Cold return water shock is often the only one talked about. It probably a very large problem with condensing boilers because they are low water content and there is no easy way of preventing this stress. It is probably a contributing factor to the typical short life of mod cons in many installation.
However, also ignored is hot shock, which occurs on system which bring on additional boilers as needed. The system may be running 180F and then the load begins to increase and an idle boiler is brought online. Full flow of 180F water into a 60F boiler cannot be good.

Corktown

I found this, @JohnNY. In the fifth paragraph down, it talks about avoiding Delta T’s above 20 to 40°F, depending on whether you’re talking about cast-iron or steel. It also mentions a number of other factors…

http://www.tti-fl.com/wp-content/uploads/2015/08/preventing_thermal_shock.doc

Corktown

I thought this part of the first paragraph on the link that I referenced was interesting:

” The term “shock” suggests a sudden impact type failure, which in the vast majority of cases is far from what actually happens.  Most failures of this type occur over a period of time, sometimes materializing within as short a time frame as a few weeks, but occasionally a considerably longer time period ensues before damage is detected.” ....

ChrisJ

Is thicker cast iron more, or less likely to crack than thin?


Thicker would be stronger, but it's also a larger difference in temperature between the two sides where's the thin should equalize faster. No?

hot_rod

JohnNY said:

I was told there is not a single documented case of a boiler cracking because someone added cold water to it while it was hot.
Does anyone know if that's true?

Told by whom?

Corktown

@Jamie Hall and @tommay, to add to your points, there’s even subtle considerations such as:

“For their part, manufacturers of cast boilers have learned to pay attention to the shape of the boiler casting.  Sharp radius corners and abrupt changes in the thickness of cast metal can amplify stresses encountered during operation.“

I found this nice little nugget at the end of the link that I provided. The notion is certainly well understood by everyone here on ‘H-H’, but is not well understood by those who don’t have “The Knowledge” (a reference to a requirement of London cab drivers before they can get their license):

“Remember that a boiler is not a light bulb to be turned on and off in an effort to conserve energy.  It is an engine that when warmed up and driven first at moderate speeds will provide both economy and long life.” ....

ChrisJ

Corktown said:

@Jamie Hall and @tommay, to add to your points, there’s even subtle considerations such as:

“For their part, manufacturers of cast boilers have learned to pay attention to the shape of the boiler casting.  Sharp radius corners and abrupt changes in the thickness of cast metal can amplify stresses encountered during operation.“

I found this nice little nugget at the end of the link that I provided. The notion is certainly well understood by everyone here on ‘H-H’, but is not well understood by those who don’t have “The Knowledge” (a reference to a requirement of London cab drivers before they can get their license):

“Remember that a boiler is not a light bulb to be turned on and off in an effort to conserve energy.  It is an engine that when warmed up and driven first at moderate speeds will provide both economy and long life.” ....

How exactly does someone "warm up and drive at moderate speeds" a typical steam boiler or single stage hot water boiler? It's either lit, or it's not?

Corktown

@ChrisJ, There’s can a bit of “looseness“ in analogies, of course. I believe what the writer was referring to, primarily, is the idea of avoiding thermostat setbacks (taking one’s foot off the gas, if you will), or at least trying to minimize them…

delcrossv

ChrisJ said:

Corktown said:

@Jamie Hall and @tommay, to add to your points, there’s even subtle considerations such as:

“For their part, manufacturers of cast boilers have learned to pay attention to the shape of the boiler casting.  Sharp radius corners and abrupt changes in the thickness of cast metal can amplify stresses encountered during operation.“

I found this nice little nugget at the end of the link that I provided. The notion is certainly well understood by everyone here on ‘H-H’, but is not well understood by those who don’t have “The Knowledge” (a reference to a requirement of London cab drivers before they can get their license):

“Remember that a boiler is not a light bulb to be turned on and off in an effort to conserve energy.  It is an engine that when warmed up and driven first at moderate speeds will provide both economy and long life.” ....

How exactly does someone "warm up and drive at moderate speeds" a typical steam boiler or single stage hot water boiler? It's either lit, or it's not?

And that's the issue right there. In a previous thread concerning boiler life @The Steam Whisperer suggested a modulating burner supplying less energy for a longer time as helpful to extending boiler life. Makes sense as Delta Temp/Delta time would be smaller stressing the boiler less.

But with regular residential installs that kind of modulation isn't provided, and with lighter castings with less water (larger Delta Temp/delta time), we're seeing shorter lifespans even if piped with preventing "thermal shock" in mind.

cross_skier

I've got insulated returns which I figure can only help

Solid_Fuel_Man

I service an old WWII airplane hanger which the town bought and has renovated extensively for their town garage.  

This place has 2 Smith boilers all piped with Victaulic. Completely new hearing system and piping done in 2008. 

I have replaced the rear section on both the boilers once. They have a "jockey" pump as @retiredguy told us about. A Taco 0012 if memory serves. The 0012 runs 24/7 basically 6 months a year here in Maine. Well both times when the rear sections were replaced the 0012 had quit. 

After replacing the pump, I proposed a flow switch in the short loop wired in series with the operating aquastat. The boilers are all on a control system and the jockey pump current is monitored. Problem is, they both seized and still were drawing current but not moving any water. 

We know what happens next.

BTW, they seized due to the massive leaks the Victaulic has in the summer and the massive makeup water. This is one of several placed we have to keep the whole loop warm during the summer to keep the water in it. 

delcrossv

Heh. Victraulic.

EBEBRATT-Ed

Oh I believe thermal shock is real. As @retiredguy mentioned it's the back section that cracks and that's where the return water goes.

The boiler manufacturers know this. I installed a Burnham that replaced a cracked Burnham in a church and Burnham's manual recommended a blend pump as retiredguy mentioned.

The Smith 28s if you by one now they use a "return water temperature stabilizer" which is a perforated pipe that goes into the back section and extends to the front of the boiler. It distributes the return water evenly to all sections (so they will all crack LOL) and promotes mixing the return water with the boiler water

ScottSecor

With regard to commercial cast iron boilers, we work on most of them. Weil McLain, Peerless, Smith, Burnham, etc. Most are located in schools, churches, apartment houses and other buildings. Of all the brands, Smith 28 series manufacturerd between roughly 1980 and 1995 were the ones with the failed rear sections most often. To this day, I'm not still not sure exactly why. I can tell you the 28 series sections were anythng but lightweight, my back still remembers buggy lugging them around.

We learned that the Peerless TC series is basically the same boiler as a Smith 28. The last few TC boilers we installed were fitted with the "return water termperature stabilizer" that @EBEBRATT-Ed mentioned above. As far as I know there have been no issues for the last six years or so with these boilers we installed.

We used to work on a lot of Cleaver Brooks firetube water boilers. They seemed to last forever if they were well maintained, On mnay of them (installed in the 1970's and 1980's) they were fitted with a realitively small "bypass pump" described above to prevent hot spots I suppose.

Most are discussing hot water boilers. What about some larger cast iron steam systems we've worked on. Boiler operator comes in Monday morning after leaving boilers off on Friday afternoon as the wather was moderate. Boilers fire up together before lead lag controls cycle one boiler off as pressure starts to rise. Every radiator is cool, so are the supply and return mains. Boiler feed tank is also full (ok tyoically one third full) of cool water. Hot boiler calls for a drink (of cool water) and nothing happens, except some steam collapses in the steam chest. This same scenario happens around here on a regular basis at schools, churches and office buildings. Yes, I realize there are Hartford loops on most steam systems, but with boiler feed systems sometimes the pumped water blasts right into the back of the boiler.

ChrisJ

The highschool I went to had two pipe steam and they would fire the boiler in the morning and shut it down by noon.

The radiators were all controlled by pneumatic thermostats

retiredguy

If you are really interested in doing a little research on steam boiler accidents, look up The Dana Corporation Paris extrusion plant, Paris, Tenn. Find the PDF from the state of Tennessee that gives an explanation of what happened to the boiler, and it's maintenance record and includes pictures. This is a typical CB high pressure boiler that had very poor maintenance, which should not have been operating. Had I have been the service tech of record, it would have been repaired or I would have called their state/insurance inspector. It ran low on water, overheated and had water introduced causing the explosion. I have seen a few of these and I am glad that I always came after the explosion. "Quite an "eye opener"

JohnNY

hot_rod said:

JohnNY said:

I was told there is not a single documented case of a boiler cracking because someone added cold water to it while it was hot.
Does anyone know if that's true?

Told by whom?

Hey, @hot_rod. I won't say his name but it was at a manufacturer's seminar a couple years ago. The statement nested in my brain immediately as something that I should look into.
Similarly, when I was taking IBR classes in the '80s-'90s, we were taught repeatedly that night time indoor temperature setback should not exceed 4° and that doing so would negate any energy savings during the recovery period.
And though I repeat it at times to those who ask, I've always wondered about the validity of that one too.

RayWohlfarth

@JohnNY This was a job that did have thermal shock

tim smith

Their was a certain mfr who had a commercial sectional that was prone to cracking near a raise boss on or near the rear section. The boss was intended for inspection plug if required. If required the boss would be threaded for plug. What we deduced was the boss would absorb additional heat during firing then the boiler would get up to temp before all cool water coming back would warm up. The crack would always be near rear return pipe connection, near that boss. These usually were old large volume systems. The mfr fix was a motorized bypass valve with return sensor to temper return.
Never quite sat well with us although true the return temps at times until heated up were coming back cooler than ideally should be.

Jamie Hall

Somewhat off topic, but it's perhaps worth noting that the efforts to maintain evenly graded temperatures in big power boilers are quite extensive -- and that almost all power boilers now have feedwater heaters either internal to the boiler or external to help. Firetube boilers, such as steam locomotives, seem to be a little less susceptible to heat shock problems (they have their own quirks: (running low on water over the crown sheet over the firebox is just not the way to a good day) but water tube boilers do have problems at times with tube to header weld failures from thermal stress.

BMC

Just fixed an 18 section peerless leaking 3 in from the back. There was boiler chemicals that attacked the gaskets. 

JohnNY

RayWohlfarth said:

@JohnNY This was a job that did have thermal shock

Jeez, I'm glad I asked this question.

DanHolohan

I am too, John!

Guru448

Hey guys I am new to posting but had to comment on this one! When I first started in the mid 80s I added water to a steam boiler that had no water and it smelled a little wierd when I walked in( only a couple of months in), and I will never forget that shrieking cracking sound of the sections. Learned a lot from that moment and I hope any other new guys will never experience that in their careers because the feelings that come along with that kind of mistake really stink(to put mildly)

EBEBRATT-Ed

When your nose speaks to you it's time to listen LOL

STEAM DOCTOR

Literally had another customer yesterday. Lwco not working. He was monitoring boiler water level (why waste money replacing lwco). Boiler dry fired. He added water. CRACK!!  

ChrisJ

I could be way off on this but my assumption was John was asking about in normal use e.g, adding water too fast to a hot boiler that's slightly low. Water that's too cold returning to a HW boiler etc.

Adding water to a dry fired empty one is going to be a bad day.