Water Hammer Basics - International District Energy Association

A Short Refresher on
Water Hammer as related to
Steam System Safety
Operation and Maintenance
21st IDEA Distribution Workshop
Miami, FL
February 21, 2011
Mark Vogler
Superintendent
Thermal Engineering
Water Hammer… as related to
Steam System Safety, Operation, and Maintenance is:
• Little known
• Often misunderstood
• Can yield catastrophic results
Trap Piping and VFD Cabinet
(out-of-sight…out-of-mind)
Sequence of Events
• Trap out-of-sight due to drip shield placement
• Trap valve was closed at some point due to
continued leakage on VFD
• Created a “manometer”
• Net-zero system flow thru period leading up to
event Halloween night, 2008
– Change in steam demand around 8:30 pm
– 3 loud bangs heard in basement
Net-Zero Steam Flow
Pipe Filled with Condensate
RESULT >> Support attachment and anchor
welds pull from pipe
Expansion joint
pulls apart
Support pulled
from ceiling
Result of Incident
• Steam discharged into mechanical room and
up pipe chase to upper floors
• Sprinklers discharge at 35 heads
• Building incurred significant water and steam
damage
• Adverse affect on research projects
• Major analysis, redesign, and repair effort
required
Goal today is to…
• Increase awareness and
understanding of Steam System:
Safety, Operation, and Maintenance
as related to water hammer
• Provide information to prevent a
similar incident at your facility
So…
What is water hammer? **
Basic definition…
Water hammer is an impact load
created by the sudden starting
or stopping of a liquid in a piping system
** NOT a WATER HAMMER
About water hammer…
• Complex Phenomenon
– Multiple factors…
– Numerous causes…
– Varying dynamics…
• Result of a transient condition
– (e.g. rapid change from moving to not moving)
• Wide variety of types…ranging from simple to complex
– Household – washing machine, dish washer, icemaker
– Plants – pumps, valves, process machinery
– Piping Systems
• Facility (house), process, distribution, service, etc
True or False?
• To create a water hammer in a steam
system, you must have high-velocity
steam to “push” a slug of water fast
enough to cause damage to the system.
•
•FALSE
Low steam flow with this incident…
Near-zero Flow here…
only 1.3 psid Imbalance Needed
True or False?
You can bleed condensate
past a gate valve if you “go slow.”
FALSE
The results can be disastrous…
True or False?
Only higher-pressure
steam can create a
“really dangerous” water hammer.
FALSE
Water hammer can occur even
with lower-pressure steam…
So…
What is
needed to create
condensate-induced
(aka “bubble collapse”)
water hammer in a pipe?
• Closed piping system
• Sub-cooled Condensate (>40 F)
• Flowing Steam
How is CIWH caused?
Begin with pipe and condensate…
Pipe
Condensate
Add flowing steam…
Pipe
Steam
Condensate
As condensate level rises,
steam velocity and turbulence increases…
Pipe
Steam
Condensate
As steam velocity and turbulence increase,
“waves” develop…
Pipe
Steam
Developing
“waves”
Condensate
Eventually, steam becomes “trapped,”
and resultant steam bubble collapses…
Pipe
Trapped steam
bubble
Steam
Condensate
When steam bubble collapses…
BANG !!
As void
collapses
Pipe
BANG !!
Steam
Condensate
BANG !!
Collapsing bubble is what makes
condensate induced water hammer
BANG !!
dangerous…
Void created from
condensing steam
…and creates a (Dp) pressure
pulse where Dp = .5(rcDV)
…or Dp = .5rV2
Steam
Is rapidly closed
KEY ELEMENTS:
•Density (r)
•Volume of void
•Velocity generated in closing void
(approaches speed of sound in water)
BANG !!
Steam Bubble Collapse w/initial Net-Zero Flow
Steam Bubble Collapse Creates Pressure Pulse Loading
Pressure Pulse Ruptures Pipe
Potential causes of excess
condensate buildup…
Riser
Live steam sloped
against a closed valve
Live
Steam
Low spot
in system
Cold-Starts
Un-insulated piping
Re-Starts
Clogged/isolated
steam trap
Steps to avoid
Water Hammer:
•
•
•
•
•
•
Keep systems drained
Keep systems properly maintained
Perform routine inspections
Keep steam piping insulated
Keep insulation DRY
During start-ups
–
–
–
–
–
ALWAYS drain water before introducing steam
NEVER mix steam with sub-cooled condensate
Provide venting
Do not get in a hurry, Energize Slowly
Drain, Drain, Drain…
Some key points…
Water Hammer is:
A Complex
Phenomenon…
Varying
Dynamics
Caused by
Multiple Factors
Numerous
Causes
Different
Types
Beyond Complex…Water Hammer can be:
Damaging to property…
Also…Water Hammer is:
Very Dangerous
it can KILL…
Good News Though…Water Hammer is:
Preventable
Drain bottom of risers
Avoid sloping live steam
against a closed valve
Live
Steam
Drain low spots
in system
Start-up Slowly
Ensure proper
trap placement
Keep traps working
Keep piping insulated and dry
Special Consideration…
Drain Downstream Side of Valve
If valve closed for long
period of time…
Provide drain of downstream side
of valve before energizing system
Live
Steam
Remember…
•
•
•
ALWAYS keep water drained from
steam system piping
If you’re unsure, ASK
DO NOT Guess
Additional
Resources:
Credits:
- ABS Consulting
-
Con Edison, New York, NY
Kirsner Consulting
MIT Utilities
Vanderweil Engineering
Trade Associations
International District Energy Association
http://www.districtenergy.org/
Consulting Engineers (training)
http://[email protected]
Energy Service Provider
Equipment Suppliers
Mark Vogler
Supt Thermal Engineering
Citizens Energy Group
(317) 927-4632
[email protected]
Questions?
21st IDEA Distribution Workshop
Miami, FL
February 21, 2011
Mark Vogler
Superintendent
Thermal Engineering
Citizens Steam Generation
• 1.99 million lb/hr
+ 500 mlb/hr steam from trash
• 2009 - over 6 billion lbs
• 28 Miles Dist Piping
• ~250 customers
–
–
–
–
5 hospitals
Research laboratories
University Campus
Lucas Oil Stadium
Citizens Chilled Water
• 74,800 Total Tons
–
–
–
–
WSCW – 36,000 tons
ISCW – 8,500 tons
IUPUI (North Plant) – 5,500 tons
2 Satellite Plants – 4,800 tons
• 2010 – over 121 mil THr
• 14 Miles Dist Piping
• ~50 customers
–
–
–
–
West Street Chilled Water Plant
2 hospitals
Research laboratories
University Campus
Lucas Oil Stadium
An Example of a Bubble Collapse Incident…
Manhattan Skyline – July 18, 2007
East 41st & Lexington Ave
Aftermath