Low Pressure Steam Bellow Failure 3

[Designer80]

I have a question.
Recently one of our Low press Saturated steam ( 6.5 barg) mettalic expansion bellow got ruptured.when steam was isolated for few minutes (30 mins) and then again opened through crack opening the manual valve (shown in the sketch).A hammer sound appeared and bellow ( encircled in the sketch) got ruptured.We have checked any possibility of condy logging through reverse flow of condensate in the steam line which could have resulted hammering and consequently failing the bellow.
Can you please share your experience, what could have gone wrong and what precautions we can take in future?

 

[LittleInch]

Lengths, pressures, temperature in the different sections would be useful as well as any slopes.

That section between steam trap offtake and the valve and then the downstream section.is important.

 

[EdStainless]

I know that said that the valve was open slowly but considering that some valve styles will give you 80% of flow with very little opening you may have just pulsed to too hard.
That said I do think that LI is on the right track.

 

[RVAmeche]

Any idea how old/how many cycles the expansion joint experienced? They're by nature consumable items that need to be replaced which is why some clients don't allow them. The norm unless otherwise specified is ~2,000 cycles.

 

[TBP]

Which way do your steam lines slope? Steam lines MUST slope - 1/2" in 10 feet for steam lines is typical. And they must slope to a drainage point for the condensate, typically a drip leg, with a trap installed. A manual valved free-blow drain valve is also good practice. Make sure that the trap and the free blow drain aren't plugged with rust & debris. Depending upon the slope of the steam line, there might have been enough steam condensing in the line to have a puddle of condensate form against the closed manual valve. If you had that situation, you experienced "condensation induced water hammer". Note that if you have conditions for condensation induced water hammer, you CANNOT open the valve slowly enough to prevent it. I experienced that first hand years ago, on a 3" 10 PSIG steam line. Nothing failed, but it made a HUGE impression on me, and my co-worker. At the time, we didn't understand what caused this water hammer event. Eventually, I discovered that this type of water hammer is caused by the steam bubble that is introduced into a relatively cold slug of condensate laying against the downstream side of a closed valve when it's cracked open. This steam bubble collapses instantly, and the inrush of water filling the vacuum left by the bubble generates a huge pressure spike - often resulting in leaks, and sometimes component failure, such as bellows expansion joints. Over the years, there have also been a number of fatalities recorded in incidents like this. Lots of things to consider when designing, installing, maintaining and operating steam systems.

 

[Designer80]

Which way do your steam lines slope? Steam lines MUST slope - 1/2" in 10 feet for steam lines is typical. And they must slope to a drainage point for the condensate, typically a drip leg, with a trap installed. A manual valved free-blow drain valve is also good practice. Make sure that the trap and the free blow drain aren't plugged with rust & debris. Depending upon the slope of the steam line, there might have been enough steam condensing in the line to have a puddle of condensate form against the closed manual valve. If you had that situation, you experienced "condensation induced water hammer". Note that if you have conditions for condensation induced water hammer, you CANNOT open the valve slowly enough to prevent it. I experienced that first hand years ago, on a 3" 10 PSIG steam line. Nothing failed, but it made a HUGE impression on me, and my co-worker. At the time, we didn't understand what caused this water hammer event. Eventually, I discovered that this type of water hammer is caused by the steam bubble that is introduced into a relatively cold slug of condensate laying against the downstream side of a closed valve when it's cracked open. This steam bubble collapses instantly, and the inrush of water filling the vacuum left by the bubble generates a huge pressure spike - often resulting in leaks, and sometimes component failure, such as bellows expansion joints. Over the years, there have also been a number of fatalities recorded in incidents like this. Lots of things to consider when designing, installing, maintaining and operating steam systems.

Thank you for your insightful reply. We dont have a drip drain and for slope , i am going to check

 

[Designer80]

Any idea how old/how many cycles the expansion joint experienced? They're by nature consumable items that need to be replaced which is why some clients don't allow them. The norm unless otherwise specified is ~2,000 cycles.

This is an old bellow and since you have pointed this out, i am not sure but i guess it must have completed its life as well.

 

[TBP]

Check the guides and pipe anchors associated with the failed expansion joint as well. Expansion joints have very specific guiding & anchoring requirements, which are typically included in the installation instructions.

 

[RVAmeche]

Sounds like a mix of potentially sub-optimal piping design and expansion joint failure due to extended life time.

I would hope the system has normal slope and drain spacing otherwise you'd be experiencing a lot more hammer events like TBP described. Accelerating slugs of condensate to ~150 fps is not great for the system.

 

[TBP]

I haven't spoken to - or even thought about this guy for years - but this is where I learned about condensation induced water hammer:

Condensation Induced Water Hammer | Marietta, GA | 770-953-8262

Kirsner Consulting Engineering investigates steam accidents due to water hammer in steam systems and does seminars for steam workers and engineers on understanding waterhammer in Steam systems.

www.kirsner.org

Condensation induced water hammer is often FAR more destructive than the typical fast moving slug of water that is most often viewed as the only reason for water hammer.

 

[EdStainless]

This subject came up with a buddy of mine the other day.
They had multiple bellows in similar service, and one would fail about every two years while others lasted much longer.
It turned out that under specific circumstances they were putting lateral load on that one bellows.
They braced that line and it fixed the issues.
Check details.

 

[LittleInch]

Also what type of manual valve?

Gate would squirt steam under the bottom lip. My guess is that the FCV was wide open so they was nothing to stop the sudden bang as described above.

Or if it was fully closed then you have a shock reaction force as soon as the valve is opened.

 

[Designer80]

This is an old bellow and since you have pointed this out, i am not sure but i guess it must have completed its life as well.

i think life cycles are already completed

 

[pierreick]

Hi,
Is their possibility to replace the bellow with another piece of equipment? let say expansion lyre.
Pierre

 

[Designer80]

Also what type of manual valve?

Gate would squirt steam under the bottom lip. My guess is that the FCV was wide open so they was nothing to stop the sudden bang as described above.

Or if it was fully closed then you have a shock reaction force as soon as the valve is opened.

FCV was closed but it has slight passing .Manual valve is "Gate" Type

 

[Designer80]

Hi,
Is their possibility to replace the bellow with another piece of equipment? let say expansion lyre.
Pierre

we are trying to do dynamic stress analysis to install a solid pipe but so far model is failing

 

[TBP]

Is it possible that the "bang" was not a water hammer event, but a expansion guide and/or anchor point failing when the line heated-up on restart, which lead to the bellows failing?

 

[Designer80]

Is it possible that the "bang" was not a water hammer event, but a expansion guide and/or anchor point failing when the line heated-up on restart, which lead to the bellows failing?

The field operator who was opening the manual Gate valve heard hammering and informed control room.he immediately closed back the valve.As soon as he heard hammer sound, leakage from bellow started and a lot of condensate started to splash from the damaged bellow. Line supports and guides are checked and are found intact without any issue.

 

[LittleInch]

"Can you please share your experience, what could have gone wrong and what precautions we can take in future?"

You got quite a bit of item 1
What went wrong is now fairly clear as to a probable cause (Condensate lying against the manual gate valve with subsequent large pressure fluctuations when opened, especially with the FCV nearly closed). Plus a very old bellows.

Precautions - Don't close the manual valve or if you do, don't use it to the restart without draining the downstream section. Swap the position of the manual valve and FCV or use the downstream isolation valve? Replace the manual valve with a plug or globe valve. Buy a stronger bellows.

 

[TBP]

There are also slip-style expansion joints for steam that can be used instead of bellows. I personally LOATHE bellows expansion joints, for exactly this type of failure.

First choice - if there's enough space - expansion loops. Second choice, slip-style. If there's absolutely no other choice - bellows.

I would urge everybody to look at the articles & links on the Kirsner's website I linked above. I would also highly recommend "Hook-Ups - The Design Of Fluid Systems" by Spirax-Sarco. It was my go-to steam system book for decades, and it never let me down.