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HAMMER, Transient Analysis and
Design - Results Tables/Questions/Answers
Version: V8i (SELECTseries 3)Units: Metric
This document has been created so that you
can easily input your answers into the resultstables and answer the questions.
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Mar-12 2 Transients in an Unprotected Pipeline - Q and A
Copyright 2012 Bentley Systems, Incorporated
Transients in an Unprotected
Pipeline - Q and A
Results Tables
Alternatives
Without
Protection
HT-1 Air Valve Surge Tank
with Check
Valve
Surge Tank
no Check
Valve
SRV
Pressure (Maximum Transient) @ PJ2(bars)
Pressure (Minimum Transient) @ PJ2(bars)
To be completed in Workshop:
Pipeline Protection
Vapor Volume (Maximum Transient)@ P2 (L)
Head (Maximum Transient) @ P5 (m)
Alternatives Junction Pressure (Maximum Transient) (bars)
PJ2 J2 J3 J4 J5 J6
Steady State Pressure 9.8 6.5 6.4 7.2 7.6 3.6
Max. Allowable Pressure 14 14 14 14 14 14
Without Protection
Hydropneumatic Tank(HT-1)
Air Valve To be completed in Workshop: Pipeline Protection
Surge Tank with CheckValve
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Mar-12 3 Transients in an Unprotected Pipeline - Q and ACopyright 2012 Bentley Systems, Incorporated
Results Tables
Surge Tank no Check Valve To be completed in Workshop: Pipeline Protection
SRV
Alternatives Junction Pressure (Maximum Transient) (bars)
PJ2 J2 J3 J4 J5 J6
Steady State Pressure 9.8 6.5 6.4 7.2 7.6 3.6
Max. Allowable Pressure 14 14 14 14 14 14
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Mar-12 4 Transients in an Unprotected Pipeline - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
Workshop Review
Now that you have completed this workshop, lets measure what you have
learned.
Questions
1 Where does the largest vapor pocket occur and what is its maximum
volume? Explain the mechanism behind the development of this vapor
pocket.
2 Select the Time History for P1:J1and click on Animate. When does the
vapor cavity at junction J1start to form and when does it close?
3 What happens to the flow at J1 at about 13.5 sec and what effect does
this have on the vapor cavity?
Enter your answer below:
Enter your answer below:
Enter your answer below:
Hint: In the Transient Results Graph you can click on the Data tab for easier viewing of graphvalues.
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Mar-12 5 Transients in an Unprotected Pipeline - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
4 Considering your answers to the previous questions and the role of the
vapor cavity in the transient event, what are some of the possible
strategies for reducing the upsurge?
5 Why is the pump (PMP1) not subjected to the transient upsurge?
Enter your answer below:
Enter your answer below:
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Mar-12 6 Transients in an Unprotected Pipeline - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
Answers
Alternatives
Without
Protection
HT-1 Air Valve Surge Tank
with Check
Valve
Surge Tank
no Check
Valve
SRV
Pressure (Maximum Transient) @ PJ2(bars)
31
Pressure (Minimum Transient) @ PJ2(bars)
-1.0 To be completed in Workshop:Pipeline Protection
Vapor Volume (Maximum Transient)@ P2 (L)
446
Head (Maximum Transient) @ P5 (m) 723
Alternatives Junction Pressure (Maximum Transient) (bars)
PJ2 J2 J3 J4 J5 J6
Steady State Pressure 9.8 6.5 6.4 7.2 7.6 3.6
Max. Allowable Pressure 14 14 14 14 14 14
Without Protection 31 27 27 28 31 26
Hydropneumatic Tank(HT-1)
Air Valve
Surge Tank with CheckValve
To be completed in Workshop: Pipeline Protection
Surge Tank no Check Valve
SRV
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Mar-12 7 Transients in an Unprotected Pipeline - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
1 Where does the largest vapor pocket occur and what is its maximum
volume? Explain the mechanism behind the development of this vapor
pocket.
The largest vapor pocket occurs at J1 with a maximum volume of 446.4 L.
Water is being pumped up a steep rise to a well-defined vertical bend or
knee at node J1, after which the pipe turns about 90 degrees to levelout with a slight fall. After the pump trips and the vapor pocket forms,
water being pumped up the rise decelerates at a much faster rate than
the water in the more level pipeline after the knee. This causes the vapor
pocket to expand at the knee (J1) as these columns of water separate.
2 Select the Time History for P1:J1and Animate it. When does the vapor
cavity at junction J1start to form and when does it close?
The first vapor cavity opens at about 8.8 sec (when flow reaches zero) and
closes just after about 13.8 sec., when a large pressure rise occurs.
Note: Transient Tip: The first vapor pocket at a well-defined knee (J1) usually opens-up as flow in the upstream segment (P1) reaches zero: the departing liquid
column in the downstream pipe (P2) actually leaves a vacuum behind at J1.
This allows you to correlate the flow and volume graphs to get the
approximate start time of 8.8 seconds.
3 What happens to the flow at J1 at about 13.8 sec and what effect does
this have on the vapor cavity?
Flow returns from Res2 and results in a negative flow, or flow reversal, at
J1. This in turn causes the vapor pocket to collapse and results in a high
pressure upsurge.
4 Considering your answers to the previous questions and the role of the
vapor cavity in the transient event, what are some of the possible
strategies for reducing the upsurge?
Mitigating the formation of the vapor cavity is at the heart of the solution.
This could be achieved by installing a surge tank or gas vessel to ensure
that water is supplied to the area where the cavity would form without
surge protection.
5 Why is the pump (PMP1) not subjected to the transient upsurge?
The time history at the pump shows that the check valve closes before
these pressure waves reach the pump (zero flow), effectively isolating itfrom the system and protecting it against damage.
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Mar-12 8 Pipeline Protection - Q and A
Copyright 2012 Bentley Systems, Incorporated
Pipeline Protection - Q and A
Results Tables
Alternatives
Without
Protection
HT-1 Air Valve Surge Tank
with Check
Valve
Surge Tank
no Check
Valve
SRV
Pressure (Maximum Transient) @ PJ2(bars)
31
Pressure (Minimum Transient) @ PJ2(bars)
-1.0
Vapor Volume (Maximum Transient)@ P2/P-9/P-11/P-13/P-15 (L)
446
Head (Maximum Transient) @ P5 (m) 723
Alternatives Junction Pressure (Maximum Transient) (bars)
PJ2 J2 J3 J4 J5 J6
Steady State Pressure 9.8 6.5 6.4 7.2 7.6 3.6
Max. Allowable Pressure 14 14 14 14 14 14
Without Protection 31 27 27 28 31 26
Hydropneumatic Tank(HT-1)
Air Valve
Surge Tank with CheckValve
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Mar-12 9 Pipeline Protection - Q and ACopyright 2012 Bentley Systems, Incorporated
Results Tables
Surge Tank no Check Valve
SRV
Alternatives Junction Pressure (Maximum Transient) (bars)
PJ2 J2 J3 J4 J5 J6
Steady State Pressure 9.8 6.5 6.4 7.2 7.6 3.6
Max. Allowable Pressure 14 14 14 14 14 14
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Mar-12 10 Pipeline Protection - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
Workshop Review
Now that you have completed this workshop, lets measure what you have
learned.
Questions
1 What effect does placing the gas vessel at J1 have on the formation of the
vapor cavity and the transient pressure spike?
2 Based on your investigation of other protection equipment, what might
be the most effective strategy for protecting the pipeline from transient
pressures?
3 How effective is the SRV in reducing the formation of vapor cavities?
Enter your answer below:
Enter your answer below:
Enter your answer below:
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Mar-12 11 Pipeline Protection - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
Workshop Results
Alternatives
Without
Protection
HT-1 Air Valve Surge Tank
with Check
Valve
Surge Tank
no Check
Valve
SRV
Pressure (Maximum Transient) @ PJ2(bars)
31 15 31 13 10 12
Pressure (Minimum Transient) @ PJ2(bars)
-1.0 6 4 4 8 3
Vapor Volume (Maximum Transient)@ P2/P-9/P-11/P-13/P-15 (L)
446 0 0 0 0 379
Head (Maximum Transient) @ P5 (m) 723 486 603 489 460 530
Alternatives Junction Pressure (Maximum Transient) (bars)
PJ2 J2 J3 J4 J5 J6
Steady State Pressure 9.8 6.5 6.4 7.2 7.6 3.6
Max. Allowable Pressure 14 14 14 14 14 14
Without Protection 31 27 27 28 31 26
Hydropneumatic Tank(HT-1) 15 11 10 10 9 4
Air Valve 31 22 21 21 22 14
Surge Tank with CheckValve
13 10 9 10 11 6
Surge Tank no Check Valve 10 7 6 7 8 4
SRV 12 11 13 14 15 11
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Mar-12 12 Pipeline Protection - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
Answers
1 What effect does placing the gas vessel at J1 have on the formation of the
vapor cavity and the transient pressure spike?
The gas vessel effectively stops the formation of a vapor cavity at J1 and
other locations along the pipeline. The high pressure spike resulting fromthe collapse of the vapor cavity is therefore eliminated.
2 Based on your investigation of other protection equipment, what might
be the most effective strategy for protecting the pipeline from transient
pressures?
The simple surge tank might seem like the most favorable alternative but
the construction of a 60 m tall tower would definitely rule this out as a
practical/economical option. The simple surge tank with check valve
would be a better option provided the system can accommodate a shortperiod of relatively low pressure that occurs just after pump shut down.
Alternatively the hydropneumatic tank is an excellent option in terms of
controlling transients, though, as a pressure vessel, the construction and
maintenance costs are likely to be higher than a simple tank. A cost
benefit analysis on these options is required to come up with the final
decision.
3 How effective is the SRV in reducing the formation of vapor cavities?
The SRV is effective in confining the occurrence of sub-atmosphericpressures to a small portion of the pipeline adjacent to SV-1 and Res2,
however a sizable vapor cavity is allowed to form near SV-1. The reason
for this is that the SRV works to control the symptoms (high pressures)
and not the cause. Other strategies are directed at restricting the
formation of the vapor cavity.
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Mar-12 13 Network Risk Reduction - Q and A
Copyright 2012 Bentley Systems, Incorporated
Network Risk Reduction - Q
and A
Workshop Review
Now that you have completed this workshop, lets measure what you have
learned.
Questions
1 Select Path1 in the viewer and click animate. When does the vapor cavity
open and collapse?
2 What causes the vapor cavity to collapse and what happens to the local
pressure when it does?
Enter your answer below:
Enter your answer below:
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Mar-12 14 Network Risk Reduction - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
3 Why is the upsurge resulting from the pump restart less than that for the
initial pump shutdown?
4 How long does it take the system to return to near steady state
conditions?
5 Apart from the area adjacent to junction J1 where else in the network do
you find appreciable formation of vapor cavities?
Enter your answer below:
Enter your answer below:
Enter your answer below:
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Mar-12 15 Network Risk Reduction - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
6 Given that the subdivision may contain older pipes, what can you say
about the transient pressures that are experienced in the network,
especially along Path3?
7 What effect has the addition of the subdivision had to the transient
pressures in the main transmission line (Path1)? Set up the pump trip as
per Lesson 1 and compare the results to those obtained in that lesson to
confirm your answer.
8 Experiment to learn the sensitivity of this system to an automatic,
emergency shutdown and restart:
Set different shutdown and restart ramp times for the pump. Forexample, try 10 second ramp times for the pump. How fast does the
flow decrease to zero? Why?
Enter your answer below:
Enter your answer below:
Enter your answer below:
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Workshop Review
Select different time delays between the pump shutdown and restart.
What happens if you try to restart the pump when pressure is at its
lowest, rising, or highest?
9 What are the fastest ramp times and shortest time delay which do not
result in unacceptable transient pressures anywhere in the system? Since
the maximum transient envelopes depend on these two variables, several
valid solutions are possible.
Enter your answer below:
Enter your answer below:
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Mar-12 17 Network Risk Reduction - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
Answers
1 Select Path1 in the viewer and click animate. When does the vapor cavity
open and collapse?
The vapor cavity begins to open and about 8 seconds and collapses at 16
seconds.
2 What causes the vapor cavity to collapse and what happens to the local
pressure when it does?
The flow returning to the pump station causes the vapor cavity to collapse
and results in a large pressure upsurge at junction PJ2.
3 Why is the upsurge resulting from the pump restart less than that for the
initial pump shutdown?
The flow generated by the pump restart helps to prevent subsequent
formation (and therefore collapse) of vapor cavities. The pump restarts at25 seconds or 20 seconds after the start of the emergency pump
shutdown, just as the high-pressure pulse from the collapse of a vapor
pocket at node J1 is reaching the pump station. This pulse closes the
check valve against the pump for a while, until it reaches its full speed and
power at around 30 seconds.
4 How long does it take the system to return to near steady state
conditions?
The system approaches a new steady state after 50 seconds and it has
essentially stabilized to a new steady state by 90 seconds.
5 Apart from the area adjacent to junction J1 where else in the network do
you find appreciable formation of vapor cavities?
There is appreciable vapor formation at the localized high point in the
network at junction J19.
6 Given that the subdivision may contain older pipes, what can you say
about the transient pressures that are experienced in the network,
especially along Path3?
Maximum transient pressure heads are of the order of 100% above
steady-state pressures along the majority of Path3. This is likely to be
very significant compared to the pipes surge-tolerance limit.
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Mar-12 18 Network Risk Reduction - Q and ACopyright 2012 Bentley Systems, Incorporated
Workshop Review
7 What effect has the addition of the subdivision had to the transient
pressures in the main transmission line (Path1)? Set up the pump trip as
per Lesson 1 and compare the results to those obtained in that lesson to
confirm your answer.
The subdivision has the effect of dampening the transient pressures.
(Pump Shutdown scenario in Lesson3_Workshop 3_answer.wtg)
8 Experiment to learn the sensitivity of this system to an automatic,
emergency shutdown and restart:
Set different shutdown and restart ramp times for the pump. For
example, try 10 s ramp times for the pump. How fast does the flow
decrease to zero? Why?
Select different time delays between the pump shutdown and restart.
What happens if you try to restart the pump when pressure is at its
lowest, rising, or highest?
With a 10 second ramp time, the flow decreases to zero in 7.3 seconds
after the pump shutdown starts (versus 4.3 seconds for a 5 second ramp
time). With different time delays, there are only minor differences in the
results.
9 What are the fastest ramp times and shortest time delay which do not
result in unacceptable transient pressures anywhere in the system? Since
the maximum transient envelopes depend on these two variables, several
valid solutions are possible.
The pump needs to ramp down slowly in order to avoid negative
pressures at J19, so the ramp down time should be 140 seconds or more.
The resulting gradual ramp down means the delay before ramping up can
be very short (5 seconds or less), since the system doesnt need extra time
to stabilize. The pump can ramp back up to full speed relatively quickly
(approx. 5-10 seconds) without causing significant high pressure
transients.
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Mar-12 19 Multipoint Network Protection - Q and A
Copyright 2012 Bentley Systems, Incorporated
Multipoint Network Protection
- Q and A
Workshop Review
Now that you have completed this workshop, lets measure what you have
learned.
Questions
1 Do vapor cavities or subatmospheric pressures occur in the protected
system?
2 Are high transient pressures experienced in the subdivision network?
Enter your answer below:
Enter your answer below:
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Mar-12 20 Multipoint Network Protection - Q and A
Workshop Review
Answers
1 Do vapor cavities or subatmospheric pressures occur in the protected
system?
No sub-atmospheric pressures occur anywhere in the distribution
network.
2 Are high transient pressures experienced in the subdivision network?
High transient pressures are comparable to the steady-state pressures for
the downstream half of Path3-1. Keeping transient water pressures within
a narrow band reduces complaints and it could be important for certain
industries.