Controlling Surges in Pipelines Hrl

Company Confidential

Date: 05-12-2010

Controlling Surges In Liquid Pipelines

By: Clay Carroll


Surge Overview

What is Surge?


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


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.


Surge Overview

All liquid piping systems are susceptible to

surge effects

• Mainline systems• Loading/unloading• Process• Households


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.


Surge Overview

Example of a pipeline without surge protection


Surge Overview

Y Split


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.


Terminology

Design Pressure MAOP/MAWP Over Pressure Set Pressure Wave Speed Effective Valve Closure Surge Pressure


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


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.


Terminology

Over Pressure

Pressure increase over the set pressure of the surge relief device expressed in units of pressure or percent of set pressure.


Terminology

Set Pressure

The gauge pressure where the surge relief valve starts to open.


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.


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%


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).


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.


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)


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.


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.


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)


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.


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


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



Heavy Wall Pipe

Disadvantage is weight and cost.



Rupture Discs

Costly to maintain due to single use Costly loss of product due to non-automatic reset



Spring loaded relief valves

Relatively low flow capacity makes this impractical

Slam shut device



Pilot Operated Relief valves



Surge Relief valves

660.000 BPD @ 1700 PSI

12” = 660.000 BPD

Cantidad : 1




660.000 BPD @ 1700 PSI

3 X K X 4 = 73.000 BPD

Cantidad : 9



660.000 BPD @ 1700 PSI

3 X K X 4 = 90.000 BPD

Cantidad : 8

Pilot Operated Relief valves



Hydraulic Accumulators

Requires accurate sizing due to limited capacity

Internal bladder is an elastomer Small size usually requires multiple

accumulators to relieve pipeline pressure



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


N2 Loaded Surge Valve


Nitrogen Panel


Total System


Pilot Operated Surge Valve

Principle of operation – Pilot Operated


Typical – Pilot Operated P&ID


Surge Event

Typical surge event is over in a few seconds


DOT Regulations49CFR195.428


Date

PRESENTATION TITLE

Speaker Information

Useful Design Information


Nitrogen Loaded Pop Test - Inline


Pilot Operated Pop Test - Inline


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.


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.


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.


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.


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


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


Pumping Station

Surge Tank

MOV

SRV SRV

Pump

INLET OUTLET

Typical Applications

MOV

Pump Station


Hose Disconnect

Storage Tank ESD

MOV

SRV

Pump

Loading Arm / Hose

TANKER


Ship Loading


MOV

SRV

Inlet Outlet


Main Line Block Valve


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.


Questions

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