Post on 30-Oct-2014
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Date: 05-12-2010
Controlling Surges In Liquid Pipelines
By: Clay Carroll
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Surge Overview
What is Surge?
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Surge Overview
Sudden, rapid flow rate changes in a pipeline generate pressure waves
Pressure waves travel both upstream and downstream from the point of origin
Pressure increases and decreases rapidly Wave speed propagation velocities range from 1100
ft/sec (334 m/sec) for water to 3300 ft/sec (1000 m/sec) for a typical oil pipeline
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Surge Overview
Pipeline surges are created by:
Slamming of non-return (check) valve Closure of ESD valves Starting and stopping of pumps Closure of MOV valves (at < 5 seconds per valve
diameter inch)
Note: Most surges are created by operator error.
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Surge Overview
All liquid piping systems are susceptible to
surge effects
• Mainline systems• Loading/unloading• Process• Households
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Surge Overview
Problems from inadequate surge protection:
Axial separation of flanges Pipe fatigue failure of welds Longitudinal pipe splits Pumps knocked out of alignment Severe damage to piping and supports Damage to specialized components such as loading
arms, hoses, filters, bellows, etc.
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Surge Overview
Example of a pipeline without surge protection
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Surge Overview
Y Split
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Surge Overview
Un accidente en la central hidroeléctrica de Sajano-Shushenskaya por la explosión de un transformador, La explosión ha generado una onda expansiva que afecto a la rotura de algunas conducciones y causo la
inundación de varias salas.
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Terminology
Design Pressure MAOP/MAWP Over Pressure Set Pressure Wave Speed Effective Valve Closure Surge Pressure
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Terminology
Design Pressure
Highest pressure, at the maximum temperature, expected during the most severe plant or pipeline operating conditions.
This pressure is always equal to or less than the MAOP/MAWP
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Terminology
MAOP / MAWP
Maximum gauge pressure permissible in the piping system at the designated temperature.
Note: Pipelines are cover by ANSI B33.4.
Plant piping is covered by ANSI B31.3.
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Terminology
Over Pressure
Pressure increase over the set pressure of the surge relief device expressed in units of pressure or percent of set pressure.
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Terminology
Set Pressure
The gauge pressure where the surge relief valve starts to open.
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Terminology
Wave Speed of the Fluid
Velocity of sound in the fluid flowing in the pipeline.
This is the speed at which surge pressures are transmitted along a pipeline.
Range from 1100 ft/sec (334 m/sec) for water to 3300 fps (1000 m/sec) for a typical crude oil pipeline.
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Terminology
Effective Valve Closure
Period over which the MOV or ESD valve reduces the flow from approx 90% of steady state to zero.
Butterfly valve: Last 15% Ball valve: Last 25% Plug valve: Last 30%
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Terminology
Surge Pressure
The rapid change in pressure as a result of change in pipeline flow rates.
Conversion of kinetic energy (velocity) into potential energy (pressure).
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Equations
Joukowski Equation
h= C ∆V/ g
Legend: h = head change (pressure)C = wave speed ∆V = fluid velocity changeg = gravitational constant
Only variable and key to surge control is to keep the ∆V
down in steps to stay within pressure rating of thepipe and flanges.
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Equations
Simplified Surge Formula
From Pipeline Rules of Thumb Handbook:
P = 0.8 wV
Legend:P = pressure rise (psi)w = liquid density (lbs/ft3)V = velocity change (ft/sec)
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Equations
Example
Pipeline operating pressure: 600 Psig (41.3 Barg)
Pipeline fluid velocity: 10 ft/sec (3.03 m/sec)
Media: Crude Oil, density = 50 lbs/ft3
ESD valve trips and closes down the pipeline
(velocity = 0)
Using P = 0.8 wV, calculated pressure rise = 400 Psi (27.59 Bar)
If this was a ANSI 300# rated system (785 Psig / 54.14 Barg),
Surge pressure would be above MAWP.
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Equations
Surge Formulas – Rule of Thumb
Pressure will rise about 50 PSI for each one (1) foot per second of fluid velocity change
(Metric) Pressure will rise about 10 Bar for each one (1) meter per second of fluid velocity change.
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DOT
U.S. Dept of Transportation (DOT)
Pipeline Regulations
49 CFR Part 195.406
Pipeline operators must protect their pipelines to
within 110% of the maximum allowable operating
pressure (MAOP) (ASME/ANSI B31.4 Piping Code)
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Design
Design Approaches to Alleviating Surge Pressure in Pipelines
Computer modeling of pipeline hydraulics during the initial stages of project
Staged ship to shore telecommunications Staged pump shut-down sequence(s) Staged emergency shut-down (ESD) or motor operated (MOV)
actuators to control valve closure times Rule of thumb is; <5 secs per inch of NPS valve size will likely cause a
surge event (e.g. 24” NPS valve needs at least 120 seconds) Selection and installation of proper surge pressure relief
equipment at or near source of surge event.
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Design
Typical surge pressure wave propagates at
1000 m/sec (3600 km/h)
This translates into a minimal amount of response time
Surge control measures must be fully automatic and
incredibly fast
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Solutions to Pipeline Surges
Heavy wall pipe (i.e. over design system) Rupture Disk Spring loaded relief valves Hydraulic accumulators Nitrogen or pilot operated surge relief valves
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Solutions to Pipeline Surges
Heavy Wall Pipe
Disadvantage is weight and cost.
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Solutions to Pipeline Surges
Rupture Discs
Costly to maintain due to single use Costly loss of product due to non-automatic reset
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Solutions to Pipeline Surges
Spring loaded relief valves
Relatively low flow capacity makes this impractical
Slam shut device
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Solutions to Pipeline Surges
Spring loaded relief valves
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Solutions to Pipeline Surges
Pilot Operated Relief valves
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Solutions to Pipeline Surges
Surge Relief valves
660.000 BPD @ 1700 PSI
12” = 660.000 BPD
Cantidad : 1
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Solutions to Pipeline Surges
Spring loaded relief valves
660.000 BPD @ 1700 PSI
3 X K X 4 = 73.000 BPD
Cantidad : 9
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Solutions to Pipeline Surges
660.000 BPD @ 1700 PSI
3 X K X 4 = 90.000 BPD
Cantidad : 8
Pilot Operated Relief valves
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Solutions to Pipeline Surges
Hydraulic Accumulators
Requires accurate sizing due to limited capacity
Internal bladder is an elastomer Small size usually requires multiple
accumulators to relieve pipeline pressure
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Solutions to Pipeline Surges
Nitrogen or pilot operated surge relief valves
Best solution
Automatic reset Very fast – response time less than 100 msec (1/10 sec.) Doesn’t slam shut High capacity
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N2 Loaded Surge Valve
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Nitrogen Panel
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Total System
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Pilot Operated Surge Valve
Principle of operation – Pilot Operated
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Typical – Pilot Operated P&ID
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Surge Event
Typical surge event is over in a few seconds
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DOT Regulations49CFR195.428
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Date
PRESENTATION TITLE
Speaker Information
Useful Design Information
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Nitrogen Loaded Pop Test - Inline
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Pilot Operated Pop Test - Inline
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Surge Valve Design Codes
Surge relief valves are designed to ASME B16.34, ASME B16.5.
Seat leakage per FCI 70.2 Valve sizing (Cv) is done per ISA 75.01 Do not apply API or ASME VIII codes to these types
of valves – as they do not apply.
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N2 Loaded Valves
Pros Opens at the speed of the surge wave No process media enters the plug cavity (only
Nitrogen) Very few parts to maintain in the valve (simple
design) Valve of choice for any dirty or viscous service
Cons Does required periodic N2 cylinder replacement.
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Pilot Operated Valves
Pros Self operated (does require a upstream line tap) Valve of choice for clean refined products in valve
sizes 4” and below
Cons Filter on valve will plug in dirty services (crude oil,
etc.) Valve full open time is slowed due to limited pilot
capacity.
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Surge Detection
Use thermal dispersion type flow switches.
Install downstream of surge valve.
***Do not use flow meters or paddle type flow switches.
Highly recommend Fluid Components FLT93S or
Magnetrol (TD2) for this application.
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Information required for Hydraulic Analysis
Process flow diagrams P&ID’s Isometrics or piping routing Pipe specifications Equipment datasheets Operating procedures Flow utility diagrams Young's Modulus Pump head/flow/efficiency and power/characteristics
Valve information Design & normal operating conditions Operating temps Fluid viscosity Fluid density Vapor Pressure Critical pressure
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Information Required for Valve Sizing
Set Pressure Back pressure Process media Name Desired relief flow rate Specific gravity Viscosity Vapor & Critical pressure Flowing & design temps Design pressure Allowable overpressure (10% is typical) Inlet/outlet pipe sizes & schedules
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Pumping Station
Surge Tank
MOV
SRV SRV
Pump
INLET OUTLET
Typical Applications
MOV
Pump Station
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Hose Disconnect
Storage Tank ESD
MOV
SRV
Pump
Loading Arm / Hose
TANKER
Typical Applications
Ship Loading
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MOV
SRV
Inlet Outlet
Typical Applications
Main Line Block Valve
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What is the difference between pressure relief valve and surge relief valve?
The pressure relief valve start to open at a set pressure and que flow capacity and lift increase as increase the pressure in the system, usually the overpressure rise a 10%
above the set pressure.In a Surge relief valve the valve open 100% when the system rise the set pressure and the accumulation on the system it is less than 2%, ussually that valves do not change the fluid direction to handle hight flow capacity. That valves prevent a liquid
hammer, the standard PSV did not.
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Questions