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safe distance from a steam pipe that ruptures
7

safe distance from a steam pipe that ruptures

safe distance from a steam pipe that ruptures

(OP)
In light of the recent fatalities at the japenese nuclear plant caused by the rupture of high pressure steam pipe which caused fatal burns, could someone tell me how I could estimate what safe distance a person needs to be away from the pipe in case of rupture.

My steam pipes carry 10barg saturated steam. I've been told that a temperature of 70C is sufficient to cause fatal burns.

  

RE: safe distance from a steam pipe that ruptures

You could predict the jet penetration distance using  the same correlations used to predict steam jet penetration length from steam sparger pipes installed in condensers.  One would also need to know the critical heat flux needed to burn the skin.

On the other hand , you would never know when or where the failure would occur, so what is the point of knowing how far away to stand from an unknown location?

If 70 C at 10 barg is a concern, I guess we should be real worried about the leaks from a 250 bar,g 565 C HP main steam line . Knowing what I now know regarding the way the P91 piping has been fabricated , maybe I should buy some life insurance.

In 1988, there was a steam line failure at the Mohave station in Nevada, USA. The hot reheater P11 pipe failed , at 31 bar,g and 593 C temp ( design temp was only 540 C, and it was overheated for 1 yr prior to failure). It failed outside of the plant cafeteria, and killed 11 operators who were eating lunch in the cafeteria.

In 1998, there was a new coal fired plant in China  which expereinced a slag fall , where a 50 ton piece of coal slag  fell 60 meters to the furnace hopper. It casued the furnace feeders to fail, and discharged 200 bar g saturated liquid ( which flased into steam) at 343 C,, and killed 22 workers who were rodding out the hopper slag trap.

RE: safe distance from a steam pipe that ruptures

If you operate on the roads, you live with the specter that a head on collision could take you at any moment.

If you work around steam pipes, you live with the specter that the grim reaper could call your number at any time.

Is any distance safe??  In some areas, the steam velocity and the temperature might not get you, but you might suffocate when the atmosphere was replaced with steam.

I am not pessimistic, only a realist.  Unsafe practices are accidents looking for a place to happen.  A lot of what our profession is all about is preventing others from getting killed.

One of the first lessons taught me when I was introduced to steam shipboard was to always have an escape route.  Since the boilers were deep in the bowels of the ship, the old hands route was to pull the deck plates up, and jump into the bilge water below, rather than chancing a 10 meter climb up a ladder in a live steam atmosphere.

I have never forgotten that.

Now, where did VPL get that soapbox emoticon.  I need it now.

rmw

RE: safe distance from a steam pipe that ruptures

to add a correction to a prior post:
The failure in China was on 10 Mar 93 at the BeiLunGang plant, Zhejiang province, and 23 workers were killed

RE: safe distance from a steam pipe that ruptures

You don't design for a pipe to fail. Operators don't stand next to pipes (only engineers do when it's sunny). Besides, I guess the safe minimum distance depends a lot on the kind of rupture. I would spend the time and money on better ways to improve plant safety!

RE: safe distance from a steam pipe that ruptures

while all postings are of value, there is a book titled "what went wrong" that describes "case histories of process plant diasters".

i believe the 5th edition is now available.

i consider books of this type to be of high value to designers, engrs, etc. whom are involved with plant design (process, power, etc.).

perhaps other forum readers may offer additional reading recommendations.

-pmover

RE: safe distance from a steam pipe that ruptures

Pmover, Who is the author of this book and where can I find it?

RE: safe distance from a steam pipe that ruptures

ss123, In some facilities there is the hard and fast rule that "NO ONE is allowed in operational areas except by permit that is controlled by the operations superintendant" These are issued on a daily as needed basis only. Reason being, processes go critical, equipment fails, piping fails, instrumentation fails, etc. By minimizing individual exposure, you minimize potential injuries and deaths.

Hope this helps.
saxon

RE: safe distance from a steam pipe that ruptures

(OP)
I would like to thank everyone for your responses to date. I would still like to hear from anyone who has done some design calculations to estimate the distance the jet of steam needs to travel from the ruptured pipe before its temperature reaches 70C.

I've estimated the steam velocity for 10.5 barg and 320C to be about 325m/s assuming choked flow . However, what happens beyond this point involves some complicated heat and mass transfer between the steam jet and the entrained ambient air.

Can anyone help?

RE: safe distance from a steam pipe that ruptures

My first thought is that you might simplify things (ALOT) and try to apply API gas dispersion formulas based on steam properties to estimate dispersion distance horizontal and vertical for the steam jet in air.  Then separately approximate jet temperature at various dispersion distances based on a simple ratio of steam to air concentration.  I envision obtaining two answers, one baserd on dispersion and the second based on temperaure drop; with best estimate based on a plot of the two functions.

I will think about this somemore, as there are surely more precise methods to model this, but the above is as close as I can think of using already developed formulas.

The more you learn, the less you are certain of.

RE: safe distance from a steam pipe that ruptures

(OP)
Thanks CHD01 for your comments. Could you direct me where I can find the API gas dispersion formulas? Also, to put an extra spanner in the works, the temperature drop of the calculation will also involve taking into account the latent heat of condensation, and subsequently the flow of the jet will quickly become 2-phase flow.

I've thought of another idea as well. That is to think of the problem as being like the a steam ejector, where the choked flow of the steam entrains the ambient air. One can then assume that this mixes instantly with the steam and so cooling it rapidly. Do you or anyone have any idea as to what the entrainment rate of atmospheric pressure air into a steam jet produced by a supply of 10.5bar steam is? Alternatively, do you think this approach is ok?

RE: safe distance from a steam pipe that ruptures

davefitz,

The accident in China was caused by the operating company continuing to operate the boiler against all good sense and advice even though it was aware of the slag build up.

As you can imagine the American company that suppied the boiler is very sensitive on this matter.

athomas236

RE: safe distance from a steam pipe that ruptures

2
ss123,

Your question should be, "What measures are commonly taken to inspect, evaluate, maintain and test high energy piping systems ?" It is, in my opinion, impractical to develop "exclusion zones" around all complex industrial, commercial steam systems. Part of the answer to that question is incorporated in the recommended mainteneace programs found in the ASME B31.1 piping code appendices.

You should also note that in the late 1980s, the USNRC has developed and enforced a nuclear piping inspection and asssesment program under the diretion of the Electric Power Research Institute (EPRI). This program involves identifying and ultasonically testing of suspect locations where erosion/corrosion may exist. The program was implemented because of a feedwater piping failure in a nuclear plant in Virgina (as I recall)

Pmmover,

The book that you are refering to is titled "What Went Wrong ?" by Trevor Kletz (now in the Fourth edition and available on AMAZON). It is, essentially a valuable casebook on process plant disasters, but has little mention of steam piping systems. Kletz followed this book up with a sequel called "Still Going Wrong " which is more of the same. Kletz hates process plant management who seem to care for little besides the bottom line. He also scorns a system where there is, essentially, no "lessons learned mechanism".....this, plus his black and bitter sarcasm, make him one of my favorites.

davefitz,

I too am curious about the nature of this steam piping failure...however Japan runs mostly PWRs and the operating temperature range of the steam systems means that mostly plain carbon steel systems will be in use. The failures that you mentioned happened mostly with Hot Reheat steam piping fabricated from A335-P11 (1.25 Gr - 1 Mo) with an axial welded seam. After some time at elevated temperatures, the seams gave out due to high temperature creep failure. Many utilities replace the P11 with higher alloy P22 (2.25 Cr - 1.25 Mo) or P91 materials. EPRI again led this effeort for the utilities.

Gimmie a star....

my opinions only

  

RE: safe distance from a steam pipe that ruptures

In over 25 years of working around steam systems, the two guys (who I both knew personally) who suffered the worst burns, suffered them from LOW PRESSURE CONDENSATE. Most people are pretty careful around steam - especially high pressure steam. Condensate usually gets treated much more casually. One of the men was in hospital for several days before they were even sure he would live. His accident was caused by someone else doing something careless & stupid. He was off work for a year. The second man was hospitalized for weeks, and off work for months. I can't prove it, but I firmly believe that his accident was due to downsizing/understaffing. Having anyone, let alone someone in their late '50s, doing a physically demanding job 6 or 7 days a week, with the days often extending 10 - 12 hours, for months on end, is just an accident waiting to happen. It's a good thing he stayed on his feet, because if he'd fallen, he'd likely be dead You can be very badly injured by having your work boots filled with 200*F condensate.

RE: safe distance from a steam pipe that ruptures

MJCronin:
No star yet.

The Mohave hot reheater pipe failure was due to several errors, all of which are being repeated today ( with P91) and which are inviting similar failures.

The Mohave unit was designed according to an early 1960's ASME section I code, which  overestimated the high temperature allowable stress for SA335-P11 piping, and did not provide for a weld creep strength reduction factor when the weld is utilized in longitudinally welded piping ( as typically used in reheater piping).

 The plant was a slurry-coal fired plant , which experienced excessive slag buildup in the furnace waterwall , which led to high furnace exit gas temperatures and resulted in hi-hi hot reheater steam temperatures,beyond the ability of the reheater attemporator spray to control to the 1005 F design temperature. The unit was operated for about 1 year at 100F over design temperature, which leads to a creep life that is about 20 times shorter than if operated at the correct design temp of 1005. F. To date , ASME section I does not proibit such operation above design temperature.  The pipe failed near an elbow , at a weld that was already weld repaired twice for prior evidence of creep cracking and seepage.

Similar errors are being repeated today with the widespread use of SA335-p91 , which has apparently been implemented in an incorrect manner. The engineers and designers who have specified this alloy are generally not familiar with the extra precautions needed for fabrication of components with advanced creep resistant steels. In particular, hot bending is not being accompanied by normalization and tempering, and when normalization is done it has not been accompanied by the correct cooling rate ( not less than 9F./min  min permitted cool rate to avoid ferrite formation)and requisite hardness testing and photomicrographs  are usually lacking. Similar errors are being promulgated at large dissimilar metal welds ( as at turbine stop valves) and welding procedures in general have not included the appropriate low hydrogen procdures and correct post weld heat treatments. And, of course, and explicit weld creep strength reduction factor is not yet defined by code .

RE: safe distance from a steam pipe that ruptures

A likely way to get a burn is not so much a pipe rupture, but a pressure relief device activating properly and flooding an area with steam.  It's tempting to write "Vent to safe location" on a drawing and forget about it.

Apologies if this has been raised previously!

Philbob

RE: safe distance from a steam pipe that ruptures

ss123,

All good posts!  The best way is to have a good piping design, the right materials of construction, a qualified installation, a proof test,  and a never ending test and inspection program with timely maintenance.

Some of the previous posts mentioned the resulting steam flow jetting into the area and how to get a feel for that.  What I didn't see was - what is the effect of the expanding steam at the instant of rupture.  A good way to get a feel for that is calculate the work the steam would do on the environment IF the entire piping instantly disappeared.  This work would be the integral of P dV.  Convert that into equivalent pounds of TNT and look up separations based on that.  There's lots of references out there for this.

This may require some abstract thinking to apply, like how long of a run of pipe do I consider, but it'll give you a feel for this component of a steam pipe rupture.

Good luck,
Latexman

RE: safe distance from a steam pipe that ruptures

Latexman (chemical) On the work term, how would one look at the change in volume, ie in a fixed rigid compartment, volume would be constant?
However, if rigid, one could compute the pressure build up from internal energy change.   U(kj of compartment and what was a finite source)   =U (initial of compartment) + U(initial of finite source.

RE: safe distance from a steam pipe that ruptures

Sailoday,

I was envisioning the area where the pipe ruptured to be open, or large, or small with sufficiently large openings that the resisting pressure to the expansion would essentially be atmospheric pressure.  W = ? Pres dV, where Pres is the resisting pressure.  At time 0-, the steam is at some high pressure and confined by the piping.  At time 0, the pipe disappears but the steam is still at this high pressure.  At time 0+, the steam has expanded to atmospheric pressure.  Initial V would be the compressed steam and final V would be steam at atmospheric pressure.  This is basically a closed system that becomes open.

If the steam pipe ruptured inside an “air tight”, closed compartment, your method would be correct.

Good luck,
Latexman

RE: safe distance from a steam pipe that ruptures

In above post, ? = Integral sign.

Good luck,
Latexman

RE: safe distance from a steam pipe that ruptures

Latexman
If we consider the downstream volume to be extremely large, the internal energy analogy that I suggested should still work.  For smaller volumes with relief openings, we would have to consider a  mass energy anlysis for the downsteam room. And that can be a messy analysis.
Regards
sailoday28

RE: safe distance from a steam pipe that ruptures

Refer to API 521, Section 4; you may also want to look at its appendixes.  Note that inclusion of referenced formulas depends on the version of API that you have, it may not be in some of the later versions.

The more you learn, the less you are certain of.

RE: safe distance from a steam pipe that ruptures

Briefly served on the Iwo Jima in the 60's. It was a converted WWII aircraft carrier and used for vertical assaults and for retrieving astronauts from the Pacific. It was decommisioned shortly after this failure ('97).

RE: safe distance from a steam pipe that ruptures

Interesting read.  Back to ss123's original question.  Looks like there was no part of that boiler room that was safe in this incident.  I wonder if any of them even tried to get into the bilges.  (see my post of Aug 12 to understand this last comment.)

rmw

RE: safe distance from a steam pipe that ruptures

Classic case of SNAFU. I'm surprised we don't have more disasters. A bolt is a bolt, a stud is a stud, a nut is a nut and parts is parts. Right?

One question, where was the officer in charge of repairs?

saxon

RE: safe distance from a steam pipe that ruptures

Hacksaw,

The DDG I served on in the 60's, the USS Conyngham, DDG-16 was scrapped shortly after a fwd fire room fire caused by an exploding fuel oil pump back in the '90's as I remember it.

Strange, this was one of the first series of ships in the USN that was 1,200 PSI steam, and the older hands (I was green) who had worked with 600 PSI steam for lots of years were scared to death of it.

But that, in the end, was not what got this ship.

I worked on that firing aisle where the pump failed.  Eirie when I think about it.

rmw

RE: safe distance from a steam pipe that ruptures



pays to be a little scared with steam

RE: safe distance from a steam pipe that ruptures

LuizSouza,

The author of the book in question is Trevor Kletz.  He has also produced many other great safety books.

Hacksaw is right, it pays to be a little scared of steam, because one thing Trevor Kletz points out in an early book is that the single most dangerous chemical we use is nitrogen, you know that big part of the air we breath.  We get so complacent about using for inerting flammable atmospheres that we forget it kills.

RE: safe distance from a steam pipe that ruptures

You have received some very good responses here. I am a little late in replying to your post, but have nearly 30 years experience in the chemical industry and as many of the other post contributors here, have experienced the hazards of steam firsthand.

Things that CANNOT be over-emphasized are:
- Assure yourself that your system is adequately designed and is OPERATED ACCORDINGLY. I use "adequate design" as an all-inclusive term which includes proper engineering of your system, correct materials used in construction, appropriate construction procedures used, proper gaskets, etc. In regard to protecting personnel from ruptured steam pipes, it is much better to PREVENT an occurrence from happening in the first place.
Seemingly minor components such as pipe supports or gasket thickness can play a significant role in overall system integrity (or failure) under the right circumstances.
With all of the downsizing and staffing cutbacks it is becoming much easier for a system to be operated outside of its' design limits and going unnoticed, until problems develop. Computerized control systems often help by notifying personnel when safe operating parameters are exceeded, but only when the warning is heeded and acted upon.

- The response about the aging workforce and long hours is right on the money. I was seriously burned years ago (and I wasn't THAT old at the time either) when a steam hose ruptured under 200 psig pressure. I was only six inches away when it blew, and it removed almost two square feet of skin from my stomach and back. I was working a double shift, was tired, normally wouldn't have had my body in the awkward position that it was, and most likely would have noticed signs that indicated the hose needed to be replaced before I used it.

- Don't ignore seemingly impossible (or highly improbable) events. In cold weather, a failed steam trap in the right place can result in pipe fittings freezing, which can crack and then burst when the weather warms and the line thaws out. I have actually watched a 20-foot section of pipe "unscrew itself" and blow off - carrying many yards away - when a elbow fitting on one end froze and then burst when it thawed out while the rest of the line was still under steam pressure.

Good engineering should not only consider the overall purpose and design of a system, it should also include the potential for operational upsets, equipment failures, and human error / stupid acts in general. You cannot design for all possible "stupid acts", but you CAN decrease the risk if you are aware of some of the things to lookout for while a project is still in the design stage. Things you can't design around should be taken care of administratively or with personnel training. The previous post regarding restricted access to operating areas is something my plant also practices, and is a highly recommended method to minimize unnecessary risk in industrial facilities.

Steve

RE: safe distance from a steam pipe that ruptures

Maybe I'm missing something here.  If you have a reasonably large steam line exhausting into the atmosphere, you would get a large cloud of steam at that point.  If, as in the Iwo Jima example above, that line is connected to a sizable source of steam, you could conceivably have a large cloud of hot steam drifting hundreds of yards from the source, and still being dangerous.  That steam does not cease being dangerous just because it is no longer part of a "jet" being emitted from the pipe.

I can just visualize the situation where a steam line is in obvious distress, with a crowd of spectators standing behind the "Safe" line painted on the floor, to watch it blow....

RE: safe distance from a steam pipe that ruptures

As the steam jet contacts atmospheric air, it mixes with it, and cools fairly quickly - as long as there's enough air and/or a small enough leak. I've also seen several "interesting" water hammer events, and can't recall a crowd gathering. Typically everyone in the area is very much aware that something potentially bad is unfolding, and can't wait to put a significant amount of distance between themselves, and the line or equipment in question.

RE: safe distance from a steam pipe that ruptures

I was just kidding about the spectators, TBP, but you illustrate the point I was getting at- there's not a "safe" distance, other than the next county.  "If there's enough air and a small enough leak" are two factors that aren't stated in the question, which means there's really no way to determine a safe distance.

The problem strikes me as similar to the gas releases at the chemical plants.  They don't try to tell you "this far is safe".  You just evacuate cross wind and hope for the best.  In this case, the risk is thermal rather than toxic, but the same issues arise.

The original statement says a temperature of 70 degrees can cause fatal burns, but that doesn't mean 69 is safe- so the criteria for safety is open as well.

Depending on the nature of the leak, you could have flying shrapnel as well.  I remember reading of an intentional head-on locomotive collision quite a few years back, and as I recall, the damage was done by flying parts and not by steam (didn't help that the locomotives were riveted).

RE: safe distance from a steam pipe that ruptures

For what it is worth.
During world war 2, there were many fatalities aboard ships due to high pressure steam leaks.  One problem with high pressure steam is that, besides the noise, there is no way to see the plume.

Many fatalities occured by people walking through the enginer rooms -- during action -- and literally getting cut by the high pressure steam leak.  One of my seabee buddies, tells of using broom sticks to check for high pressure leaks, if the handle fell off, you found one.

Training of personnel around high pressure steam systems is recommended.  Planning to have flanges located away from areas of personnel is difficult, but can be done.

RE: safe distance from a steam pipe that ruptures

Pay a visit to:

http://www.kirsner.org/pages/articlesAlt.html

Mr Kirsner analyses steam burns, and other factors that may be relevant to this thread, in the article titled: Surviving a Steam Rupture....

RE: safe distance from a steam pipe that ruptures


A steam jet discharging to atmosphere typically becomes an eductor, and entrains a large amount of ambient air, cooling the bulk flow considerably.  This phenomenon is strongly influenced by The safe distance depends on the size of the steam pipe rupture, pressure, etc., and the surrounding enclosure.

For example, a small "Try Cock" on a 10 bar boiler is opened to test the water level in the boiler.  By passing your finger near the jet issuing from the Try Cock, the operator detects if steam (feels cool) or saturated water (feels hot) is on the other side of the Try Cock.  I have done this hundreds of times.

A small "rupture" of this size is normally harmless at 1 meter distance, but could cause problems if continuously discharging into a relatively confined space which would heat up to greater than 70C in a short time.
the local geometry.  Flashing steam/water mixtures are worse than pure steam, and have a greater potential for personnel injury in many situations.

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