Reformer TubeLifeAssessment
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Preparedby:Eitzaz Hussain
ContentsContents
Primaryreformerintroduction F2501history Tubedesignparameters Tubedamage&assessment Methodsoftubelifeassessment ScopeofLMMethod LarsonMillerMethod AnexampleofLMMethod UncertaintiesinLMMethod LimitationsofLMMethod
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Primary ReformerPrimaryReformer
Primary reformers are used to convert a process gasmixture of hydro carbons & steam into hydrogenrich gaseswhich can be used in the manufacture of ammonia. Theprocess gas is passed under pressure through vertical tubesfilled with catalyst and, since high temperature(900950 OC)is required to maintain the required chemical reaction, theoutside of the tubes are heated by burners in a largey gfurnace.
H O + CH CO + 4HH2O + CH4 CO2 + 4H2
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F2501(History)F 2501(History)
FosterWheelerdesignedTerracetype
Operated19years(19671986)inPascagoula(USA)
Mothballedfor5years(19861991)
Reconstructedwithnewradianttubes,archroofsealing,roof& wall refractory outlet pigtails and header (incoloy 800H)&wallrefractory,outletpigtailsandheader(incoloy 800H)
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Tube Design ParametersTubeDesignParameters
Designpressure Quantity 392g p
500psig
Designtemperature
Q y
Material Abex TX63
O.D 4.7inch
17800F
Theoreticaldesignlife
I.D 3.7inch
Length 42ft
100,000hours MSW 0.465inch
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Tube Damages & AssessmentTubeDamages&Assessment
Damages Damageassessmentg
Creepdamage
Thermalcycling/shock
g
Ultrasonictechnique
Eddycurrenttesting
Externaloxidation
Internalcarburization
Radiography
Dyepenetrant test
( ) Leaktest(soapsolution)
Thermography
Refractory inspection Refractoryinspection
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Methods of Life AssessmentMethodsofLifeAssessment1. Destructivestressrupturetesting
2 Larson Miller Equation (Paper study)2. LarsonMillerEquation(Paperstudy)
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Scope of LM MethodScopeofLMMethod1. Estimationoftubelifeatgiventemperature,pressure,
corrosion rate ??corrosionrate??
2. Estimationoftemperatureforspecifiedlifeatgivenpressure&corrosionrate??
3. Operatingpressure&TMTreductionfortheextendedtubelife??
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LarsonMiller MethodLarson MillerMethod Tabulationofrequireddata
Calculation of average stress Calculationofaveragestress
EvaluationofLarsonMillerparameter&constant
Rupture time calculationRupturetimecalculation
Remainingtubelife
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Required DataRequiredData Tubematerial
Tube metal temperature (TMT) Tubemetaltemperature(TMT)
Operatinggaugepressure(P)
Tube O.D (D0 )TubeO.D(D0 )
Initialminimumtubethickness()
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Average Stress CalculationAverageStressCalculationMeandiameterequation
beginning=P/2{(D0/ beginning)1}
end=P/2{(D0/ end)1}
=( + )/2 AVG=( beginning+ end)/2
=StressP=Pressure=Thickness
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LarsonMiller ParameterLarson MillerParameterLarsonMillerParameterCurves(LMvaluesaretakenagainstaveragestressfromcurves)
(S.Iunits)LMP= (T+273)(C +log t )x103LMP=(T+273)(CLM+logtr)x10
3
(US customary units)(UScustomaryunits)LMP=(T+460)(CLM+logtr)x10
3
LMP=LarsonMillerParameter
CLM =LarsonMillerConstant
tr = RuptureTimer p
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LM PARAMETER
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Graph GuideGraphGuide1. Specified minimum tensile strength2. Tensile strengthg3. Specified minimum yield strength4. Yield strength5. Elastic allowable stress6 Rupture allowable stress6. Rupture allowable stress7. Limiting design metal temperature8. Minimum rupture strength9. Average rupture strength10. Elastic design governs above this stress
Graph----Stress curves (SI units) for ASTM A 213, ASTM A 271, ASTM A 312 and ASTM A 376 types 347 and 347 H(18 Cr-10 Ni-ASTM A 312 and ASTM A 376 types 347 and 347 H(18 Cr 10 Ni
Nb)stainless steel
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RuptureTimep Calculated from LM parameters Minimum strength rupture timeMinimum strength rupture time Average strength rupture time
t r(avg) > t r(min)
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Remaining Tube LifeRemainingTubeLife Life fraction = operating period rupture time Life accumulated = life fractions Life accumulated = life fractions Remaining fraction = 1 - ( life fractions) Remaining tube life = Remaining fraction x rupture lifeRemaining tube life Remaining fraction x rupture life
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An Example
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Uncertainties in LM MethodUncertaintiesinLMMethod Tube damage
(uncertain TMT Operating pressure Corrosion rate etc )(uncertain TMT, Operating pressure, Corrosion rate etc.) Actual rupture strength is no precise Tube damage rule {t r =t r (,T)}Tube damage rule {t r t r (,T)}
(it asserts that creep rupture will occur when the life fraction totals unity)
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Limitations of LM MethodLimitationsofLMMethod Apply to thin tubes
N id ti f hiti ti b i ti No consideration for graphitization, carburization, oxidation & hydrogen attack
Apply to seamless tubesApply to seamless tubes
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For more details & information, please contact us.
thePetroStreet [email protected]