壓力管道基本概念（Basic concepts of pressure piping）

壓力管道基本概念(Basicconceptsofpressurepiping)

Basicconceptsofpressurepiping

“Theuseofcertainpressure,tubularequipmentusedfor

transferringgasorliquid,thescopeoftheprovisionsforthe

maximumworkingpressureisgreaterthanorequalto0.IMPa(g)

gas,liquefiedgasandsteammediumorcombustible,explosive,

toxic,corrosive,higherthanorequaltothemaximumworking

temperatureoftheliquidmediumstandardFeipoint,and

pipelinethenominaldiameterismorethan25mm”.Thatisto

say,the"pipeline”,notonlyreferstothepipeortubeunder

pressure,andtheinternaltransmissionmediumisgas,

liquefiedgasandsteam“or〃maycauseexplosion,toxicor

corrosiveliquids,'material.Theso-called“explosion”,

“poisoning"or'corrosive"hasthefollowingconnotations:

Dielectricexplosion:themediumisflammableandexplosive,

undercertainconditionscancausecombustionorexplosion,

leadingtofireanddestruction.Themediumincludesa

combustiblegas,liquefiedhydrocarbonandcombustibleliquid

firehazardoussubstances,butalsoeasytocauseanexplosion

ofhightemperatureandhighpressuremediumsuchassteam,

exceedthestandardboilingpointofhightemperaturehotwater,

compressedairandothercompressedgas.Amongthem,the

flammablemediumfireriskaccordingto"petrochemical

enterprisedesignfirecode”GB50160and"buildingdesignfire

code”GBJ16,isdividedintoa,B,Cthreecategories.

Theexplosivelowerlimit(volume)ofaandBflammablegasand

airmixtureisdefinedas:

Classaflammablegas:<10%;

ClassBflammablegas:10%.

Theclassificationofflammableliquidssuchasmethyl,ethyl

andpropaneisshownintable1.

Table1Classificationoffireriskofliquefiedhydrocarbons

andflammableliquids

Classnamecharacteristics

ClassAliquefiedhydrocarbons,150C,hydrocarbonliquidsand

othersimilarliquidsundersteampressure>0.IMPa

Bflammableliquid,flammableliquidotherthanA,flashpoint

lessthan280C

BAflashpointofflammableliquidwasgreaterthan280Cto

lessthan450C

Bflashpoint>450Cto600C

ClassCAflashpointofflammableliquidisgreaterthanor

equalto600Ctolessthan1200C

Bflashpoint>1200C

Note:flashpointlessthan450Cliquidiscalledflammable

liquid;flashpointbelowtheambienttemperatureiscalled

explosiveliquid.

UnderGBJ16rules,thefireriskofcombustiblemediumbelongs

totheCPI(orprocess)are:atroomtemperaturecandisassemble

oroxidizedinairthatcanleadtospontaneouscombustionor

explosionsubstance;undernormaltemperaturebywaterorsteam

canproducegasandcauseafireorexplosionofflammable

substances;inorganicacid,heat,impactandfriction,andin

catalyticorganiccompoundsorsulfur,caneasilycauseafire

orexplosionstrongoxidants;impact,frictionoroxidants,

organicmattercontactcancauseafireorexplosionsubstance;

andtheoperationtemperatureinasealeddeviceisequalto

orgreaterthantheignitionpointofthematerialitself.

ThemediumthatbelongstotypeBfirehazardmainlyrefersto

oxidantsandchemicalflammablesolidswhicharenotdangerous

toclassafire,andcombustionsupportinggases.

(B)thetoxicityofamedium:thatis,themediumhasatoxic

property.Whenthesemediaareinhaledorexposedtothehuman

body,theycancauseharmtothehumanbody,andevendeath.

Accordingtotheprovisionsofthe,'occupationofexposureto

toxicsubstances”GB5044grade,sixindexesofpoisonaccording

toacutetoxicity,acutepoisoningincidence,prevalenceof

chronicpoisoning,chronicpoisoning,carcinogenicityand

consequencesofthehighestallowableconcentration,consists

ofextremelyhazardous,highhazard,moderatehazardandmild

harmfourgrades.

Extremeharmmedium,sometimescalled“poisonmedium”,high,

mediumandmildharmmedium,iscalled"poisonousmedium””.

Toxicmedium(fluid)inthenationalstandard"ofChina's

industrialmetalpipelineengineeringconstructionand

acceptanceof”GB50235-97,sexplanationis:ifthereisavery

smallamountofthesesubstancesreleasedintotheenvironment,

canbeinhaledorincontactwiththehumanbody,eveniftreated

promptly,

Anysubstancethatcausesseriousorintractableharmtothe

humanbody.Equivalenttothecurrentnationalstandard

''occupationalexposuretotoxicantclassification”,Iin

GB5044

Apoisonofdegree(extremeharm).Thus,thetoxicmediumcan

beunderstoodasextremelyharmfu1tothemedium.Thetoxic

mediuminthestandardexplanationis:thiskindofmaterial

leakedintotheenvironment,wasinhaledorincontactwiththe

humanbody,suchastreatmentintime,nottothehumanbody

causenoteasytorestoretheharm.

However,thetoxicityofthesamelevelofpoison,inthe

specifictreatmentoftheproblem,therearedifferencesin

industries.Forexample,benzeneislistedasanextremely

hazardousmediumintheoccupationalhazardclassificationof

hazardoussubstances(GB5044).Itisalsousedasanexample

ofextremehazardousmediaintheanalysisoftheregulations

onsafetymanagementandsupervisionofpressurepipelines.And

inthe,'petrochemicalchemicalandtoxicmediapipeline

constructionandacceptancecriteria”SH3501-2002pipe

classification,benzeneistreatedwithahighdegreeofharm

medium.IncludedintheSHBclass.Incontrast,fourhighly

hazardousmedia,suchasacrylonitrile,phosgene,carbon

disulfide,andhydrogenfluoride,aretreatedinthe

SH3501-2002asahighlyhazardousmediumandincludedinthe

SHApipeline.Thiswillnotonlyaffectthequalitystandards

ofconstructionandtherequirementsforinspectionof

pipelines,butalsoaffecttheleveloflicensedivisionfor

specificprojects.Incaseofbenzenepipinginstallation,if

thebenzeneisdeemedtobeextremelyharmfultothemedium,

theconstructionunitshal1hold

GClevel1installationpermit,andasahighlyhazardousmedium,

thecertificationlevelrelatestothepipingdesignpressure

anddesigntemperature.

Explanationforthisproblemcanbeunderstoodfromthepoison

hazardgradationprinciple:thenationalstandard''occupation

ofexposuretotoxicsubstancesonthespecificgradingrating

of“poisonGB5044-85istoenumerate56poisonsinsome

industriestheharmdegreeofexpression.Butthestandardalso

pointstotheextentofharmtootherindustriesthatare

exposedtothesamepoison(whichisnotlistedinTable2of

thestandard),

Accordingtotheconcentrationoftoxicantintheairinthe

workshop,theprevalenceofpoisoningandthelengthofcontact

time,thegradeisdesignated.Whereintheairofworkplace

concentrationoftenreachTJ36-79''industrialdesign”

sanitarystandardstipulatedbythemaximumallowable

concentrationvalue,anditsprevalenceorincidenceof

symptomsislessthanthecorrespondingvalueofthe

classificationstandard,canreducethelevelof.Therefore,

itisnormalforeachspecificsubstance,nationalstandardand

professionalstandard,todifferentiatewhentheharmgradeis

divided.Becauseinadditiontocarcinogenicityandthehighest

allowableconcentrationintheair,theotherfourindicators

arerelatedtotheproductionprocessandoperation

characteristics.Petroleum,chemicalandpetrochemical

pipelinetotransportmediumbasedproductionprocess,toxic

substancesintheclosedcondition,continuousflow,depends

ontheharmofthepoisonincontactwiththehumanbodyby

accident,orbecauseofrecurrentchronicharmcausedbythe

leakageprobabilityofoccupation,usuallylowerthanthe

openingoftheproductionprocess.Therefore,inthedesignof

pressurepiping,theleveloftoxicantharmshouldbe

determinedindetail.Theconcentrationoftoxicantintheair,

theprevalenceofpoisoningandthelengthofcontacttime

shouldbedefined.

Asmentionedabove,themaximumallowableconcentrationof

toxicantintheairintheworkshopisspecifiedasfollows:

Extremehazard:maximumallowableconcentrationbelow0.1

mg/m3;

Highhazard:maximumallowableconcentrationis0.1mg/m3~1.0

mg/m3.

Accordingto“HygienicStandardsforthedesignofindustrial

enterprises'"(TJ36-79)regulations,acrylonitrile,benzene,

phosgene,carbondisulfideandhydrogenfluorideandotherfive

kindsoftoxicsubstancesinworkplaceairandairof

residentialareasinthehighestallowableconcentrationis

shownintable2:

Table2maximumallowableconcentrationofseveralpoisons

Nameofbenzene,acrylonitrile,phosgene,carbondisulfide,

hydrogenfluoride

Allowableairconcentrationinworkshop

(mg/m3)40.02.00.510.01.0

Allowableatmosphericconcentrationinresidentialarea

(dailyaveragemg/m3)0.80.05-0.04

(atime)0.007

(0.02atatime)

AsindicatedinTable2,thehighestallowableconcentration

ofbenzeneintheairoftheworkshopismuchhigherthanthat

oftheextremehazardousmedium.Atthesametime,according

tothepipelineindustryinconveyingthecontinuity,sealing

characteristics,analysisoftheprevalencerateandthe

durationofexposuretobenzenepoisoning,andoperating

personnel,benzeneshouldnotbelongtothescopeofextremely

harmfulmedium.Therefore,thedeterminationofthetoxicity

ofthemediumintheactualworkshallbebasedonthenature

ofthepoisondeterminedinthedesigndocumentorthe

constructionacceptancespecificationspecifiedinthedesign

document.

Inaddition,aboutthelengthofcontacttime,Chinahasnot

yetformulatedtherelevantstandards,theUnitedStates

governmentindustrialhygieneexpertmeeting(ACGIH)

recommendedthreeexposurethresholdvaluescanbeusedasa

reference:

1)theaverageweightedvalueofthenormal8hourworkingday

or40hourworkweekisconsideredasanindicator.Inthis

concentration,repeatedcontactwillnothaveanyadverse

effectsonallpersonnel;

2)inashorttime(eachtimenotmorethan15minutes,nomore

than4timesaday,eachtimeintervalofnotlessthan1hours)

ofthetimeweightedaverage1imitvalueastheindex,atthis

concentration,shorttimecontinuouscontactwithoutcausing

irritation,chronicorirreversiblepathologicalchanges,

increasedanesthesiaaccidentself-helpabilitydropsorwork

efficiencydecreasedsignificantly;

3)theupperlimitisthemaximumconcentrationthatshouldnot

beexceededeveninaninstant.

(C)thecorrosivenatureofamedium:asubstancethatburns

humantissueandcausesdamagetothepipematerial,suchas

acids,alkalis,andotherfluidsthatcausematerialdamage

suchashydrogenandhydrogensulfide.

(three)safetysupervisionscopeofpressurepipeline;

Accordingtotheregulationsonthesafetymanagementand

supervisionofpressurepipelines,thepressurepipelines

belongingtothescopeofsafetysupervisionarethepressure

pipesandtheirauxiliaryfacilitiesandsafetyprotection

devices,whichhaveoneofthefollowingconditions.

1)thedegreeoftoxicityisextremelyhazardoustothemedium,

irrespectiveofpressure,temperature,andcondition;

2)fireriskisthemediumofaandB,regardlessofpressure,

temperatureandstate;

3)themaximumworkingpressureisgreaterthanorequalto0.1

MPagas(steam)body,liquefiedgasmedium,notthenatureand

temperature,buttheprovisionsofthe"safetymanagementand

supervisionofpressurepipelines"arenotincludedinthe

scopeofsupervision.

4)thehighestworkingpressureisgreaterthanorequalto0.1

MPaofflammable,explosive,toxic,corrosivemediumorthe

highestoperatingtemperaturehigherthanthestandardboiling

pointofliquidmedia.

Theregulationsonthesafetymanagementandsupervisionof

pressurepipelinesstipulatethatthefollowingfourtypesof

pipelinesdonotfallwithinthescopeofsupervision:

A)pipesbelongingtothedevicebody.

(b)pipelinesinmilitaryequipment,vehicles,andnuclear

installations.

C)non-toxic,nonflammable,noncorrosivegaswithanominal

diameteroflessthan150mmandamaximumoperatingpressure

oflessthan1.6MPa.

Here,thedefinitionofthefacilitiesandsafetyprotection

devicesforpressurepipesis:

(a)ancillaryfacilitiesmainlyrefertopipingequipment,

supportsandhangers,cathodicprotectiondevicesusedfor

pressurepipelines.

B)safetyprotectiondevicesmainlyrefertoovertemperature,

overpressurecontroldevicesandalarmdevices,etc..

Note:intherecentlyissuedregulationsontheadministration

oftheregistrationoftheuseofpressurepipes(forTrial

Implementation),thedefinitionofpressurepipes,auxiliary

facilitiesandsafetyprotectiondevicesisclearlydefinedas

follows:

A)apressurepipeconsistsofapipecomponent,apipesupport,

asafetyprotectiondevice,andancillaryfacilities.Atubular

deviceforconveyinggasesorliquids;

B)referstothecathodicprotectiondevice,ancillary

facilitiesofcompressorstations,pumpingstations,valve

stationsandpressureregulatingstationsandmonitoring

system;

(c)safetyprotectiondevicesaresafetyvalves,pressure

gauges,burstingdiscsandemergency