Reformer Tube Life Assessment Thepetrostreet

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


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)


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


Tube Damages & AssessmentTubeDamages&Assessment

Damages Damageassessmentg

Creepdamage

Thermalcycling/shock

g

Ultrasonictechnique

Eddycurrenttesting

Externaloxidation

Internalcarburization

Radiography

Dyepenetrant test

( ) Leaktest(soapsolution)

Thermography

Refractory inspection Refractoryinspection


Methods of Life AssessmentMethodsofLifeAssessment1. Destructivestressrupturetesting

2 Larson Miller Equation (Paper study)2. LarsonMillerEquation(Paperstudy)


Scope of LM MethodScopeofLMMethod1. Estimationoftubelifeatgiventemperature,pressure,

corrosion rate ??corrosionrate??

2. Estimationoftemperatureforspecifiedlifeatgivenpressure&corrosionrate??

3. Operatingpressure&TMTreductionfortheextendedtubelife??


LarsonMiller MethodLarson MillerMethod Tabulationofrequireddata

Calculation of average stress Calculationofaveragestress

EvaluationofLarsonMillerparameter&constant

Rupture time calculationRupturetimecalculation

Remainingtubelife


Required DataRequiredData Tubematerial

Tube metal temperature (TMT) Tubemetaltemperature(TMT)

Operatinggaugepressure(P)

Tube O.D (D0 )TubeO.D(D0 )

Initialminimumtubethickness()


Average Stress CalculationAverageStressCalculationMeandiameterequation

beginning=P/2{(D0/ beginning)1}

end=P/2{(D0/ end)1}

=( + )/2 AVG=( beginning+ end)/2

=StressP=Pressure=Thickness


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


LM PARAMETER


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


RuptureTimep Calculated from LM parameters Minimum strength rupture timeMinimum strength rupture time Average strength rupture time

t r(avg) > t r(min)


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


An Example


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)


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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Reformer Tube Life Assessment Thepetrostreet