presentation for api 934f

5/20/2018 Presentation for API 934F

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API 934F Task Group

Procedure to Calculate the

Minimum Pressurization Temperature (MPT) for Heavy

Wall Vessels in High Temperature High Pressure

Hydrogen Service - 2Cr-1Mo

Presentation at API 934F Task Group Meeting,

September 18, 2012, New Orleans, LA

Jim McLaughlin

Consultant


2/22

Basis for Calculating the MPT of Heavy Wall Vessels in

High Temperature High Pressure Hydrogen Service

Fast Fracture Considerations

Low energy brittle fracture promoted by temper embrittlement effects

Older reactor vessels (fabricated before circa 1980) without compositional

controls to limit impurity levels, such as P, Sn, Sb and As

Newer reactor vessels (fabricated after circa 1980) with compositional

controls to limit impurity levels, such as P, Sn, Sb and As

Effect of hydrogen on fast fracturenew consideration

Slow Stable Crack Growth Considerations

Hydrogen embrittlement controls slow stable crack growth

Recent research at UVa shows that hydrogen embrittlement effects

rapidly disappear at a threshold temperature above which noembrittlement occurs

Hydrogen embrittlement effects also function of impurity levels

MPT determined by limiting temperature consideration due to fastfracture and slow stable crack growth considerations


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Fast Fracture Considerations - Temper Embrittlement Guidance

Fast fracture addressed in same manner as in Part 3 of API579, paragraph3.4.3.1, Pressure Vessels, Method A

Need to establish starting temperature for entering Figure 3.7 to establish theMinimum Allowable Temperature (MAT) as a function of the applied stress ratiofollows same temperature reduction curves as in Section VIII, Divisions 1 and 2 of

the ASME Code.

Use an estimate of the 40 ft-lb transition temperature in the temper embrittled

condition as the starting temperature

Use 250F (121C) for older reactor vessels (fabricated before circa 1980)without compositional controls to limit impurity levels, such as P, Sn, Sb and As

Use 300F (149C) for older reactor vessels without compositional controls and

made from plate with long seam made with single ESW pass

Use 150F (65C) for newer reactor vessels (fabricated after circa 1980) with

compositional controls to limit impurity levels, such as P, Sn, Sb and As

For reactor vessels with step cool requirements, use the maximum calculated orallowed temperature after the step cooling heat treatment with a 3.0 multiplier

factor

When is temper embrittlement a consideration?

Suggesting that temper embrittlement be considered only when the maximum

expected operating temperature (normally the end of run temperature) for the

reactor vessel is 700F (371C) or higher


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Effect of Hydrogen on Fast Fracture New Consideration

Effect of hydrogen on fast fracture at low temperaturesArcelorMittal data


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Hydrogen has significant effect on fast fracture at low temperatures

summary of ArcelorMittal data on 2Cr-1Mo with a very low FATT of-80C (-112F)


6/22


Test conducted on 2Cr-1Mo with high impurity levels as prepared by Kobe Steelshows that the effect of hydrogen on fast fracture at higher temperatures decreases

As the temperature approaches 150F (65C), the fracture toughness approaches 100MPam even when soluble hydrogen levels are 3 ppm, highest expected level inrefining hydroprocessing service.

Conclusion: Effect of hydrogen on fast fracture insignificant above 150F (65C)


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Combining results on the effects of hydrogen on fast fracture at low temperature

per the ArcelorMittal testing, with the results of the Kobe tests at higher

temperatures, the following curve can be used to define the shift in the fracturetoughness transition temperature that results from the effect of hydrogen on fast

fracture


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Slow Stable Crack Growth Considerations

Hydrogen embrittlement controls slow stable crack growth considerations

Hydrogen embrittlement effects as determined by a slow strain rate risingload test show that the effects disappear once the temperature reaches athreshold temperature above which hydrogen embrittlement effects areinsignificant.

Above threshold temperature reactor pressure limited to the full design

pressureBelow threshold temperature reactor pressure limited to 30% of the full design

pressure

Testing performed at UVa and data available from other sources are usedto develop curves for the hydrogen embrittlement threshold temperature

as a function of the bulk hydrogen level in the steel and the concentration

of hydrogen that can accumulate in the plastic zone a head of a crack.

Curves were developed for 2Cr-1Mo steel with high impurity levels and low

impurity levels.


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Hydrogen Embrittlement Threshold Temperature

(High Impurity 2Cr-1Mo)


10/22


(Low Impurity 2Cr-1Mo)


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Suggested Hydrogen Embrittlement Threshold Temperature

Curves for Use in MPT Assessment

Each curve represents a constant ratio of the bulk hydrogen concentration

in the steel versus the concentration at a distance of 470m from thecrack tip.

For the purposes of an assessment 3 different levels of hydrogenconcentration at the crack tip are defined. Each of these levels represent

different stress intensity levelsthe higher the stress intensity the greater

the hydrogen concentration at the crack tip

Nominal hydrogen concentration (C470m/Cbulk= 1)This is the level that wouldbe expected with a crack similar to the crack that existed in the compact

tension sample used for testing for hydrogen embrittlement

Conservative hydrogen concentration (C470m/Cbulk= 1.54)This is the level

that would be expected with a crack that has a higher stress intensity than thecrack in the compact test specimen.

Non-conservative hydrogen concentration (C470m/Cbulk= 0.5)This is the levelthat would be expected with a crack that has a lower stress intensity than the

crack in the compact test specimen.


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(High Impurity 2Cr-1Mo)


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(Low Impurity 2Cr-1Mo)


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MPT Assessment of Typical Hydroprocessing Reactors

MPT assessment for 2 typical reactor vessels

Fast fracture considerationsBoth reactors screened base materials

and welding consumables with a step cooling procedure

For this assessment the starting temperature for fast fracture curve aftertemper embrittlement effects are accounted for is 75F


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Effect of hydrogen on fast fracture

First need to determine the bulk hydrogen level in thereactor wall

The following assumptions are made for this calculation Calculation is made at the maximum expected operating

temperature and hydrogen partial pressure using the latestdiffusivity and solubility data from Kobe Steel

Assume that the cladding is cracked so that there is no benefitfrom the stainless steel cladding in reducing hydrogensolubility in the steel

No benefit calculated for outgassing during reactor shutdown


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Effect of hydrogen on fast fracture

Reactor 1 Fast Fracture Starting Point Temperature 75F + 31F = 106F

Reactor 2 Fast Fracture Starting Point Temperature 75F + 25F = 100F


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Slow Stable Crack Growth Hydrogen Embrittlement Effects


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Slow Stable Crack Growth Considerations Control Over Entire

Temperature Range for MPT Assessment

Reactor 1

Reactor 2

Low Impurity 2Cr-1Mo

Does Not

Meet MPTGuidance

Meets MPTGuidance


19/22


(Old Reactors without Compositional Controls)

MPT assessment for 2 typical reactor vessels

Fast fracture considerationsBoth reactors were fabricated prior to

1980 and did not have any compositional controls to maintain low impuritylevels

For this assessment the starting temperature for fast fracture curve aftertemper embrittlement effects are accounted for is 250F

Since the starting temperature for the fast fracture curve is above 150F,there will be no additional temperature added to the starting temperature

to account for the effect of hydrogen on fast fracture


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Slow Stable Crack Growth Hydrogen Embrittlement Effects

High Impurity 2Cr-1Mo


21/22


Fast Fracture Controls at Higher Temperatures and Slow Stable Crack

Growth Controls at Lower Temperatures

High Impurity 2Cr-1Mo

Does NotMeet MPTGuidance

Meets MPTGuidance


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Additional Work Needed on MPT Assessment Procedure

Improved understanding of the 3 curves being suggested for the hydrogenembrittlement threshold temperature as a function of bulk hydrogen levels

What are typical crack sizes/geometries indicated for each of these curves in areactor vessel

Ted Anderson will discuss further

Assumptions included in the MPT procedureAre they too conservative?

Assuming that a crack compromises the stainless steel claddingUsing the dissolved hydrogen level at the maximum expected metal

temperature and hydrogen partial pressure level without any reduction provided

for out gassing during shutdown

3 curves being suggested for the hydrogen embrittlement threshold

temperature

Use of rising load test results to define hydrogen embrittlement effects

Need to conduct testing on 2Cr-1Mo-V material

Hydrogen embrittlement effort

Effects of hydrogen on fast fracture

presentation for api 934f

Documents

temperature consideration

threshold temperature

transition temperature

starting temperature

newer reactor vessels

pressure vessels

asfor reactor vessels

high impurity levels