ML20138B338

Provides Info to Support Proposal to Perform Annual Pressure Testing as Method of Leak Detection for Underground Line That Runs from Loading Area 5,000 Barrel Aboveground Storage Tank

ML20138B338
Person / Time
Site:	North Anna
Issue date:	04/23/1997
From:	Sprouse W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Flory G VIRGINIA, COMMONWEALTH OF
References
NUDOCS 9704290130
Download: ML20138B338 (11)

Text

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• Innsbrook Technical Center 5000 Dominion Boulet ard Glen Allen. \'irguria 2J060 April 23,1997 Mr. Gary A. Flory vammaemwn AST Program Supervisor Department of Environmental Quality r

Valley Regional Water Office 4 P. O. Box 1129 Harrisonburg, Virginia 22801- 1129 Re: ODCP FACILITY INSPECTION - NORTH ANNA POWER STATION (FC-06-7030)

RESPONSE - LEAK DETECTION PROPOSAL

Dear Mr. Flory:

Pursuant to our phone conversation regarding leak detection at North Anna Power Station, we offer the following information in support of our proposal to perform annual pressure testing as the method ofleak detection for the underground line that runs from the loading area to the 5,000 barrel aboveground storage tank (AST).

The pipeline is used, under normal operating conditions, once per year. The fuel oil is used for 1 the emergency diesel generators and the Station Blackout Diesel Generator. These facilities are maintained in a state of constant readiness for safe shutdown of the nuclear units. In order to maintain the state of readiness the diesel generators are operated periodically to ensure they are functioning properly Although the auxiliary boilers are also fueled from the 5,000 barrel tank, j they are presently in dry lay-up and there are no plans to operate them in the near future. The day tanks associated with the diesel genemtors are fed from two 50,000-gallon USTs, which are in turn supplied by the 5,000-barrel AST. Unless there is a loss of power which would require use of the emergency diesels, these test runs are the only routine use of the fuel oil; therefore, the station normally receives fuel oil once per year, though there have been several occasions when fuel oil was delivered twice in one year. Thus, the underground line that runs from the loading area to the 5,000 barrel storage tank is normally used once per year. The volume of oil remaining in the pipe between deliveries is approximately 79 gallons.

The line is constructed of Driscopipe 1000. Driscopipe 1000 is made of high density polyethylene material manufactured by Phillips 66. It does not rust, rot, or corrode.

Information from the manufacturer discussing the properties of the pipe material is attached.

The maximum discharge pressure of the fuel oil fill pump is 70 psig. This is well within the operating range of the Driscopipe 1000, which, as installed, has a Standard Dimension Ratio (SDR) of 9.0 and, thus, a pressure rating of 200 psi. (The SDR is the ratio of the outside pipe diameter to the minimum wall thickness of the pipe.) The system is equipped with a relief valve )

set at 90 psig to prevent over pressurization of the pipe. The pipe was installed per e g gufacturer's recommendations and pressure tested for leaks prior to completion of backfill.

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Mr. Gary Flory April 23,1997  :

Page 2 Virginia Power is aware that the proposed pressure testing does not conform to the guidelines set '

l forth by the DEQ; however, because of the infrequent use of the line (normally once per year),

the absence of corrosion potential, and the conservative design of the pipe we feel that the potential for the line to leak is very low. We ask that you approve the use of annual pressure testing of the line to satisfy the leak detection requirement in the regulation.

As stated in my previous letter (March 24,1997) we will have the revised ODCP issued as final i

with station approvals as required by our nuclear operations procedures pending final resolution of the leak detection issue. .

We appreciate your time and consideration regarding this matter. If you have any questions please contact me at (804) 273-3552. I am available to meet with you if you feel further i discussion would be helpful to resolve this issue.

Sincerely,

f. .

l W. A. Sprouse, Jr., P.E.

Senior Engineer Environmental Policy & Compliarme Attachments cc: U. S. Nuclear Regulatory Commission Region 11 101 Marietta Street, NW Suite 2900 Atlanta, GA 30323 RE: North Anna Units 1 and 2 Docket Nos. 50-338/50-339 License Nos. NPF-4/NPF-7 U. S. Nuclear Regulatory Commission Document Control Desk I

Washington, DC 20555 l

RE: North Anna Units 1 and 2 1 Docket Nos. 50-338/50-339 License Nos. NPF-4/NPF-7 Mr. Russell Gibbs NRC Resident Inspector North Anna Power Station 1

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$ ,n, n A copy of nominal physical properties for Dnscop pe I 1000 is available from your Phillips Dnscopipe, Inc.

f H representative. Sample specifications for water distnbution, force - main and gravity flow sewers are

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Chemical Resistance J

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O Driscopipe 1000 has outstanding chemical resistance. Most chemicals, acids, salts and hot j l l l Q Q soils will not attack Dnscopipe or cause it to j degrade. It does not rust, rot or corrode. It does Introduction n t pr mote or support algae or bactena! growth.

i The Driscopipe* 1000 polyethylene piping system Flow Factors is lightweight, flexible and chernical and abrasion Dnscopipe polyethylene pipe has an extremely j resistant, allowing it to be used in a number of smooth inside surface. It maintains its excellent flow diverse applications. Driscopipe 1000 is also properties throughout its service life due to its

protected from ultra-violet degradation and thermal excellent chemical and abrasion resistance.

l degradation, giving it a long service and storage life Because of its smooth walls and non-wetting i in above ground, exposed installations. Dnscopipe charactenstics, a higher flow capacity and a reduced l 1000 can meet the National Sanitation Foundation friction loss is possible with Dnscopipe 1000, j require. 'ents for potable water. See your Philhps resulting in operating cost savings. A 'C" factor of

Dnscopipe, Inc. representative for details. 155 is used with the Hazen-Williams equation for pressunzed fluid flow and an *n" factor of .009 is Specifications used with the Manning Formula for gravity flow.

Driscopipe 1000 is a PE 3408 high density, high F ow charts and additional system design extra molecular weight polyethylene piping s.< stem. nformation are available through your Phillips it may be specified by ASTM D3350 as havWg a cell Dnscopipe Inc representative.

classification of PE 345434C. Dimensionr. and workmanship are specified by ASTM F714. Direct Burial Driscopipe 1000 is buried utilizing flexible pipe / soil system design practices. The pipe actually gains strength from the surrounding soil allowing it to l

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backfill selection, Dnscopipe 1000 may be buried at '

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i depths, a backfill of 85% of Standard Proctor j density (AASHTO-99) can limit the nog deflection of -

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Since Driscopipe pipe can be butt fused above 4

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ground in long lengths, narrow trench widths can be 4 .- l used to save on installation costs. Due to the ease . ; I of handling Dnscopipe, it may be readily placed in -

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embedment matenals, and bedding and installation practices are specified in ASTM D 2321. . .

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l Primary Properties - Cell Classification - ASTM D 3350-84 345434C*  !

! Test j Property Method 0 1 2 3 4 5 6 1- Density,9 cm' / D 1505 0.910- 0.926- 0.941- > 0.955 l 0.925 0.940 0.955 1 2- Melt index-condition E (gms/10 min.)

D 1238 > 1.0 1.0 to 0.4 < 0.4 to 0.15 < 0.15 )

3- Flexural modulus, D 790 < 138 138-< 276 276-< 552 552-< 758 758-< 1103 < 1103

M Pa (psi) (< 20 000) (20 000 to (40 000 to (80 000 to (110 000 to (<160 000)

< 40 000) < 80 000) < 110 000 160 000) l 4-Tensile strength D 638 <15 15-<18 18-< 21 21-< 24 24-< 28 < 28 I at yeild. M Pa (psi) (< 2200) (2200- (2600- (3000 . (3500- (> 4000) l < 2600) < 3000) < 3500) < 4000) I i i 5 Environmental stress D 1693 l crack resistance' l

a. Test condition A B C

b. Test duration. h 48 24 192 j c. Failure, max, % 50 50 20 I 6. Hydrostatic D 2837 NPR* 5.52 6.89 8.62 11.03 design basis. (800) (1000) (1250) (1600)

M Pa (Psi), (23'C)

Color and UV Stabilizer A B C D E Natural Colored Black with Natural Colored 2% minimum with UV with UV carbon black stabilizer

• NPR = Not Pressure Rated

' NOTE: Refer 1o Dnscopipe 1000 Data Sheet for complete nominal physical properties occumentation. features / advantages / benefits.

and listings of major industnal and municipal applications.

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I Dnscopipe pipe may be cold-bent to a minimum J

radius of 20-40 times the pipe diameter as 11 is Temperature Ranbe installed, thus eliminating the need for elbows at Dnscopipe 1000 may be used in pressure l

slight bends. The minimum bending radius which applications up to an operating temperature of

can be apphed to the pipe without kinking vanes witn 140'F. Short term and gravity flow applications

the diameter and wall thickness of the pipe. Operating at higher temperatures are considered.

If adequate space is not available for the required At lower temperatures. tests have been conducted j on Driscopipe 1000 showing that Driscopipe gains

radius, a fitting of the desired angle may be fused into the piping system to obtain the necessary strength at sub Zero temperatures. Dnscopipe l 1000 maintains its flexibihty and integnty to lower i change in dacction.

i than -180cF.

i The pressure capabilities of polyethylene matenals Trench Construction and Terminology are rerated for operating temperatures otner than 73.4*F. Dnscopipe 1000 has been tested for thousands of hours at elevated temperatures without t

$w I'"[e c thermal degradation. These tests are used to obtain the pressure rerating factors.

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$,I"l Temperature, Degree F Pressure Rerating Factor j v2 Diameter bP""9 50 1.14 top Fill "

unch 73.4 1.00 100 0.79 I

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i. *in Suttable SOi!S the COnStruCtlOn Of a bedding and'Or a tOundation Il rnay not L@ recluired "Gravily flow ()n5COprpe Sewers rnay be accurately laid to grade ,

Ur.ing laSW Leam SCOP;ng.

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I l Joining System 3. Specify The Correct 0.D. Of The Liner ),

Dnscopipe is joined by the fusion technique. Normally, if the old line is in reasonable

! This simple, visual procedure utilizes controlled condition, a 10% clearance is adequate temperature and pressure to produce a fused, for sliplining. ,

leak free joint stronger than the pipe itself in both 4. Prepare The Liner l tension and hydrostatic loading. Pioneered and Determine and measure lengths of p:pe required. i developed by Phillips, the heat fusion joint is Fuse the single joints into prescnbed l recognized in the industry as a joining system of lengths and attach pulling head

• and tag line l

high integnty and reliability. Dnscopipe may a!so be if required.  ;

l joined to itself and transitioned to other materials 5. Clean The Line

• i with flanges, compression couplings and other Clear and clean the old line sufficiently in order l mechanical means.

to insert the liner without undue stress.

insert Renewal (Sliplin.ing) 6. Insert The Liner Establish pulling cable and rig. Attach cable

1. Inspect The Line to pulling head and slope excavation minimum A TV survey will locate laterals, defects and of 2:1; then pull the liner into place. Alternately, provide the best insight on how to repair the line. the liner may be pushed into place using a

2. Economically Select choker strap.

Excavations For Insertion 7. Close The Job i From the TV survey and engineenng drawings. Properly seal or grout around liner at manholes i locate excavations at cave-ins or changes in and cut inverts. Close excavations.

line or grade.

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• See P.D.I. tech note #20 on pull head design.

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i Pull Technique y Manhole T e L ner Existina Pipehne --

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12 x OD I The Liner Existing Pipehne f - _ ,

J A Dnscopepe represei.'ative can adese you on song your liner for external water head and other factors. Design brochures and repnnts of ASTM F 58548 " insertion of Hexible Polyethylene Pipe into Existing Sewers" are available on request.

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i j insert renew sewers to save money l while enhanca g conimunity relations o fi/ppqg" f

• Streets remair 09.1 to tre'nc t.44-p -

• Fewer excavations iewer manholes ,-

• No loss o' services

• Ouic- :: .e ad most effe:tive method o' i reDa.r/rerK val l

• 'Jo infiltrat;on w:M Strong, fused joints e Txcellent fiow properties of Dr. scop:pe will i estore the capacity of the systerm no infiltration or exfi!"ation l,I

• Low ma:ntenance, almost immune to blockages I

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• Immune to sewer gase s & most chemicals lj = ND a 3ae or bactenal buld up i

e No joint separation of butt fusions due to earth or live loads i

Additionalinformation I Technical design brochures and detailed installation brochures are available on request from a Philhps Driscopin. Inc. representative.

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! The basic Driscopipe recommendation for all HDPE STEPTWO:

,/ SYSTEM LIFE EXPECTANCY P'pe systems is to use the above design cntena and expect a 50 year life from the system Use of a higher The user of a polyethylene Driscopipe system is design stress may reduce the factor of safety as well t

primanly interested in one thing . . long, trouble free as shorten the service life of the pipe system. Any service. In order to maintain established confidence table of "Intemal Piessure Ratings" for polyethylene in the long term strength and continued performance pipe represented as safe operating working of Dnscopipe, actual pipe samples are continuously pressures should be carefully reviewed. The prudent l

i tested in accordance with ASTM procedures. engineer will double-check the hydrostatic design Standard samples of pipe are held at constant stress according to the industry accepted formula as 1

j pressure and temperature according to specifications. defined in ASTM D 2837.

i By using high pressures and temperatures some Where: S = Hydrostatic design stress i samples are forced to fail. Statistical predictions are 2 St P = Verking pressure then made as to the service life and long term P=

(D - t) D = Average outside diameter strength of the pipe based upon the number of forced t = Minimum wall thickness failures and the time it took them to fail.

This data is plotted in a specific manner and this d' STEPMEE-SYSTEM PRl5SSUREREQUIREMENTS brvhves dNn te reIat nsh e e ntn expected " life" of the pipe and the iriternal stress at a Most pipeline % stems are designed for one of three given working pressure and temperature. Refer to the types of service:(a) pressurized flow;(b) non.

Engineenng Charactenstics brochure of this manual pressurized flow; (c) vacuum flow, When designing a for a typical stress-life curve. The " Hydrostatic Design pressurized pipe system, the pipe selected must hold Stress" (HDS) as shown on the stress-life curve is the the internal pressure safely and continuously. In a estimated maximum te:isile stress in the wall of the non-pressurized system such as a gravity flow sewer, pipe in the circumferential direction due to internal pipe selection depends on other f actors.

hydrostatic pressure that can be continuously applied with a high degree of certainty that pipe failure will not Vacuum piping systems must use pipc which will resist collapse. For each invallation ine design

( occur. The HDS is calculated by dividing the long 1erm strength by a safety factor of 2.0. This factor of engineer will use different deOgn r,iteria and calculations. This

• Step Three" wers the selection of l

safety is an industry accepted standard designed to preserve the integnty of the pipeline as well as to pipe based upon intemal pressure or internal vacuum protect the public. In addition to achieving these Positive Pressure Pi lines goals, it extends the service life of the pipeline well beyond 100.000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> into the 50 and 100 year range. Steady State Internal Pressure: Phillips Dnscopipe For example, Phillips Driscopipe has tested and subscnbes to the SDR metnod of rating pressure proven Dnscopipe 8600 and Dnscopipe 1000 to pipe. SDR is the abbreviation for the " Standard conform to the following design cnteria: Dimension Ratio". What does this SDR mean? SDR is the ratio of the pipe O.D. to the minimum thickness of DRISCOPIPE 8600 and DRISCOPIPE 1000 the wall of the pipe. It can be expressed Long Term Hydrostatic Strength 1600 ps e akah as:

(6 73.4*F 6: 100.000 hrs )

Safety Factor 2.0 D = Pipe outside diameter SDR = t Hydrostatic Design Stress 800 psi in inches t = Pipe minimum wall thickness in inches 21

DD]MEe12lus \

For a given SDR the ratio of the O.D. to the minimum years with safety. The formula relating SDR and wall thickness remains constant. An SDR 11 means a A hydrostatic design stress has been adopted by ISO V W the O.D. of the pipe is eleven times the thickness of (International Standards Organization). ASTM the wall. This remains true regardless of diameter. For ( Amencan Society For Testing and Materials) and the example, a 14" diameter pipe with a wall of 1.273* is PPI(Plastics Pipe Institute) as the standard for i

i an SDR 11 pipe. An 18" diameter pipe with a wall of the industry l 1.637 is also an SDR 11 pipe. Common SDR ratios are The formula is:

SDR 9.3. SDR 11 SDR 13.5, SDR 15.5. SDR 17. SDR 19, SDR 21. SDR 26 and SDR 32.5. For high SDR t S ratios, the pipe wallis thin in companson to the pipe P = D-t or P = SDR - 1 ,

O.D. For low SDR ratios, the wall is thick in Where: P = Pressure rating (psi) comparison to the pipe O D. Given two pipes of the D = Pipe OD (inches)  ;

same O.D., the pipe with the thicker wall will be t = Minimum wall thickness (inches) i stronger thaq the one with the thinner wall. Thus, high S = Hydrostatic Design Stress SDRs have low pressure ratings and low SDRs SDR = D + t

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I correspond to high pressure ratings because of the relative wall thickness. From the formula it can be shown that al/ pipes O/ the same SDR (regardless of diameter) willhave the same The pressure rating of thermoplastic pipe is pressure rating /or a given design stress. Thus, 36" dia.

mathematically Calculated from the SDR and an SDR 32.5 has the same pressure rating as'14" allowable hoop-stress. The allowable hoop-stress is SDR 32.5. For the design engineer's reference, the commonly known as the long term hydrostatic design standard SDRs and their corresponding standard stress. It is the stress level (that has been laboratory pressure ratings for water at 73.4 F. using a tested and field proven) that can exist in the pipe wall hydrostatic design stress of 800 psi, are shown in continuously with a high degree of confidence that Charts 12 and 13. ,

the pipe will operate under pressure for at least 50 l Chart 12 Pipe Pressure Rating Driscopipe 1000 (at 73.4*F)

SDR SDR SDR SDR

$ W 1 SDR SDR SDR SDR SDR SDR 32.5 26 21 19 17 15.5 13.5 11 9 7 Long Term Strengtn (psi) 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 '

Safety Factor 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Hydrostatic Design Stress 800 800 800 800 800 800 800 800 800 800 l Design Life (min. years) 50 50 50 50 50 50 50 50 50 50 Pressure Rating (psi) 51 64 80 90 100 110 128 1"60 200 267 Chart 13 Pipe Pressure Rating Driscopipe 8600 (at 73.4*F)

SDR SDR SDR SDR SDR SDR 32.5 25.3 15.5 11 9.3 8.3 Long Term Strength (psi) 1600 1600 1600 1600 1600 1600 Safety Factor 2.0 2.0 20 20 2.0 2.0 Hydrostatic Design Stress 800 800 800 800 800 800 '

Design Life (min years) 50 50 50 50 50 50 Pressure Rating (osi) 51 65 110 160 190 220 h k 22

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V WaterHemmer/ Pressure Surge: Any moving object Where: S = Speed of the pressure wave, ft/sec i

k -[. has mass and velocrty Hence, any flowing liquid has momentum and inertia. When flow is suddenly K = Bulk modulus of the liquid, psi

= 300,000 psi for water

! stopped, the mass inertia of the flowing stream is E = Modulusof elasticityof pipe

! converted into a shock wave or high static head on material, psi

' the pressure side of the pipel;ne. Some of the more = 100,000 psi for Driscopipe i common causes of hydraulic transients are (a) the - short term

! opening and closing (full or partial) of valves, SDR = Standard Dimension Ratio, j (b) starting and stopping of pumps,(c) changes in D/t,of pipe l turbine speed, (d) changes in reservoir elevation, w = Unit weight of fluid, Ibs/cu ft (e) reservoir wave action, (f) liquid column separation g = Acceleration due to gravity

! and (g) entrapped air. = 32.2 ft/sec/sec '

a i Driscopipe can withstand hn occasional surge The excess pressure due to water hammer is:

l pressure up to 2.5 times the rated pressure capability wgyc I of the pipe without a cumulative effect. This is due to P=3 the long term modulus of the material being only a 144 9 j fraction of the short term modulus. Additionally, the Where: Ps = change in pressure, psi j flexibility and resilience of Driscopipe effectively Vc = change in velocity, ft/sec. occurring j reduce the surge pressures which may be seen in within criticaltime 2L/S i steel, concrete, fiberglass or PVC, w, g and S are as above.

1 l Quick surge pressures are shock waves known as The following example may be helpful in f " water hammer". The pressure wave due to water understanding these equations.

hammer races back and forth in the pipe getting EXAMPLE progressively weaker with each " hammer". The Water is flowing in a Driscopipe pipeline with an SDR g maximum surge pressure results when the time of 35 at a velocity of 10 ft/sec. Determine the l j required to change a flowstream velocity a given maximum pressure increase when a valve is closed j amount is equal to or less than 2 L/S such that: n a time equalto orless than 2 LJS.

d 2L Where;

{ & p ts S Where: L = Length of pipeline (feet) i V 4 S = Speed of pressure wave (ft/sec) SDR = 35 K = 300,000 psi E = 100,000 psi j t = Time (seconds) 000 m 00 m i l

S is determined from: S"12' y[62.4/32.2][100,000 + (300,000)(35)]"

KE Ps = [(62.4/32.2)(459)(10)) + 144 = 61.8 psi S = 12 -

[w/g)[E + K(SDR)) The changes in pressure can be minimized by using a valve closure time greater than 2L/S. Since the magnitude of the surge is basically a function of the time required to change the velocity, particular attention should be given to the final portion of valve closure. This is the time of maximum effect on the e ( uw.s n3 23

O D 1 M 7 els/4 -1 5 w

. velocity of the flowing liquid. The actualincreae in the strain of overpressures. If the recovery penod at a pressure caused by valve closure is difficult to determine but a closure time of 10 times 2t>S for a normal level of stress is equal to or greater than the (r -

gate valve with linear closure charactertstics should duration of the overpressunzation, Driscopipe can be reduce the pressure surge to the range of 10% to 20% subjected to the stresses of overpressurization for of the surge caused by closure in a time equal to or short periods without affecting its long term strength.

less than 2US. endurance and performance.

In generai, good system design will eliminate quick The basic limitation on short-term overpressure -

opening / closing valves on anything but very short cycles is to stay within the elastic limits of the pipe lines. The design engineer should use judgment with matenal. If the system pressure exceeds 2.5 times the rated pressure of the pipe for any length of time,

• regard to the addition of surge pressures to operating '

permanent strain or deformation of the pipe occurs.

pressures when selecting pipe SDRs. The following rules of thumb may be of help: As a resutt, the expected service life of the pipe can a be dramaticatly reduced. When overpressure cycling Because of the inherent flexibility and resiliency of is expected as a regular condition of operation, the Driscopipe, its surge pressures are significantly highest pressure anticipated for a preponderance of less than those encountered in ngid pipe under the same conditions. operating time should be considered as the operating pressure and it should be treated as though it would

. Occasional shock pressures can be accommodated persist continuously for the design life of the system.

within the design safety factor. Due to the short time 4

duration of the surge pressure, occasional shock long/tudinalStress /romIntemalPressure: When a wave surge pressures to 2.5 times the SDR futly restrained pipeline such as a buried or well I pressure rating at 73.4'F are usually allowable. anchored pipeline is pressurized, longrtudinal If surge pressure or water hammer is expected in a stresses develop in the pipe wall. The longitudinal system. keep the flow velocity on the low side of the stress is calculated as follows:

velocity range. S=t P(D - t)/ 2t If surge pressure or water hammer is expected, Where: S t= Long:tudinal tensile stress, psi maximize tN iim9 required to shut off a valve or = Poisson's rado reduce flow. A shutoff cycle 6-10 times the time ,

= 0.45 for Dnscopipe i period 2L + S is suggested to minimize surge P = Internal operating pressure, psi pressures by grad'; ally slowing the fluid flowstream.

• It constant and repetitive surge pressures are D = Pipe outside diameter, inches )

t = Pipe wall thickness, inches present, the excess pressure should be added to Thus, most pressurized pipe systems operate under the nominal operating pressure when selecting the pipe SDR. a dual state of stress: hoop stress and longitudinal stress. The longitudinal stress factor is already Cyche Overpressure: A short-term cyclic included in the pipe's pressure rating for 50 year life overpressure manifests itself in many ways. Situations at normal temperature.

such as a stuck relief valve, a plugged discharge line or repetitive freeze / thaw Cycles can cause an Non-Pressure Pipelines.

extended rise in pressure greater than the normal Gravity flow systems are representative of non-operating pressure.

pressure pipelines. In some instances there may be in steel, concrete, PVC or fiberglass pipe, the effect several feet of water head in the pipeline but usually can be devastating. With Dnscopipe, the wall is able the pressure can be considered to be low relative to to stretch (strain) with the freezing water and the pipe the capability of the pipe. In these instances, flow will return to its onginal condition af'er the frozen capacity may be the predominant design parameter water has thawed. Although some residual strain of rather than the pipe's pressure rating.

• less than 1 % may be evident, the physical properties of the pipe resin are not adversely affected and the Vacuum or Suction Pipelines performance of tne pipe at normal operating Dnscopipe may be subjected to internal pressure or i conditions is not affected. Due to the innate elastic internal vacuum. Vacuum systems usually can be characteristics of Dnscopipe, it is capable of categonzed into one of three general situations withstanding these types of cyclic loadings without applicable to most installations:

damage to the pipe's performance. The effects of Vacuum pipelines aboveground.

extended repeated overpressurization can be Vacuum pipelines underwater (submerged).

tolerated by Driscopipe within specific limits. Vacuum pipelines underground (buned).

Driscopipe has an inherent ability to " recover" from The first type is discussed here and the last two are discussed in Step Five: INSTALLATION DESIGN. 4 b

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