High Temperature Effects on Vessel Integrity - … Levin.pdf · High Temperature Effects on Vessel Integrity ... ASME Section II (July 2007) ... Materials • ASME Section VIII (

High Temperature Effects on Vessel Integrity

Marc Levin, Ayman ChetaMary Kay O’Connor Process Safety

Center2009 International Symposium

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Outline

• Motivation• Basics / Basis for Pressure Vessel Design

Conditions• Mechanical & Metallurgical Failure Mechanisms• Corrosion Failure Mechanisms• Examples• References• Summary

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Motivation

• Where pressure rise is modest, but temperature rise is significant, the impact of temperature on vessel integrity becomes more important.

• To determine the temperature when a instrumented barrier should activate, understanding of the damage potential to the vessel vs. temperature is needed.

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Motivation

• Some uncontrolled reactions can cause a temperature excursion without an increase in pressure

Methanation

Hydrogenation/Saturation

Hydrocracking

Some Decomposition Reactions• In such systems, vessel safeguarding is not

accomplished thru pressure relief devices

Cannot expect pressure relief devices to open

Rely on other barriers, e.g., instrumented systems with temperature sensing combined with emergency depressuring (manual or automatic)

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Motivation

• Potential vessel failure is still a concern because vessel integrity deteriorates at high temperature

• Exceeding the vessel ultimate tensile strength is only 1 of many potential failure mechanisms

Message: Determining the temperature where vessel damage could occur is complex; evaluating mechanical failure, such as excessive hoop stress alone, is not sufficient

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Basics• The ability of a vessel to maintain integrity at a

given pressure also depends on the temperature

- Design pressure has a coincident design temperature

- Maximum Allowable Working Pressure (MAWP) has a coincident temperature rating (note: there is no MAWT)

• Sometimes, “design temperature” is based on target operating conditions, not what the vessel can take

• Documentation might not be readily available. Thus, it might require some digging to find the b i f th t t d “d i t t ”

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Basis for Vessel Design Conditions

MechanicalDamage to vessel condition/properties

• Metallurgical – Changes in metal properties as a result of conditions

• Corrosion - Chemical or electrochemical attack as a result of its reaction with the environment

-----------------------------------------------------Target operating conditions

If design is based primarily on target operating temperature, then look for the appropriate design temperature for safeguarding vessel integrity

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Additional Considerations

Vessel Constituents• Shell• Heads• Nozzles• Welds

If one is determining the temperature and pressure a vessel can withstand, each of these needs to be examined.

A Sampling of Failure Mechanisms

• MechanicalPlastic deformation (non-reversible)

• Damage (some common mechanisms)Chemical/Electrochemical attack - corrosion

Creep - stress induced time-dependent deformation under load

ErosionFatigue – repeated / fluctuating stresses, max < mat’l tensile

strength

FractureEmbrittlement – microstructural changes at high temp, H2

Thermal stresses – non-uniform temperature distribution/differing thermal expansion coefficients

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API 571 – Damage Mechanisms Affecting Fixed Equipment in the Refining Industry - Section 4.0

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Mechanical Failure

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• Hoop (circumferential) stress• Longitudinal stress• Stresses on nozzles & welds

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Mechanical Failure (cont’d)

Metallurgical Failure Mechanisms: Selected High Temperature Cases

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Failure Mechanism

Mat’l Affected

Temp Range [F]

Description

Graphitization Carbon steel, 1/2Mo steel

800-1100°F Microstructure change after long-term, high temp. operation; carbide phases can decompose into graphite nodules

Spheroidization Carbon steel, low allow

steels

850-1400°F Microstructure change where carbide phases change from normal, plate-like

form to a spheroidal form; or agglomerate

885 F Embrittlement

400 series SS, Duplex

SS

600-1000°F Metallurgical change in alloys with ferrite phase leading to loss of toughness

Sigma phase Embrittlement

300 series SS,

400 series SS,

Duplex SS

1000-1750°F Formation of “sigma” metallurgical phase leading to loss of toughness

Creep Rupture All metals & alloys

700+°F Metal components slowly and continuously deform under load (< yield

stress) that can lead to rupture

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Metallurgical Failure Mechanisms (cont’d): Selected High Temperature Cases

Failure Mechanism

Mat’l Affected

Temp Range [F]

Description

Thermal Fatigue

All mat’ls of construction

T200°F Cyclic stresses caused by variations in temperature that can lead to cracking

where movement/expansion is constrained

Short Term Overheating – Stress Rupture

All common mat’ls of

construction

Permanent deformation at relatively low stress levels from localized overheating, leading to bulging and rupture

Dissimilar Metal Weld Cracking

Ferritic (CS/low alloy) + Austenitic (300 series

SS)

510+°F Coefficients of thermal expansion between ferritic steels and 300 Series SSdiffer by 30% or more, leading to high stress at the heat affected zone on the ferritic side.

Corrosion Failure Mechanisms: Selected Moderate-High Temperature Cases

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Failure Mechanism

Mat’l Affected

Temp Range

[F]

Description

Chloride Stress Corrosion Cracking

300 Series SS, Ni alloys

140+°F Surface-initiated cracks on exposure to tensile stress, elevated temperature, and

aqueous chloride

Caustic SCC Carbon steel, Low alloy

steels, 300 Series SS

120+°F Surface-initiated cracks on exposure to tensile stress, elevated temperature, and

caustic

High Temp. Hydrogen Attack

Carbon steel, Various alloys

450+°F H2 reacts with carbides in steel to form methane (which remains trapped) leading to cracks causing loss of

strengthCarburization Carbon steel,

Fe or Ni alloys1100+°F Contact with carbonaceous mat’l leads

to absorption of carbon into metalDecarburization Carbon steel,

low allow steels

Removal of carbon/carbides from steel at high temperature, leaving an iron matrix and causing loss of strength

Oxidation Carbon steel, Fe or Ni alloys

1000+°F Metal converted to metal oxide

Sulfidation Fe, Ni, or Cu 500+°F Reaction of metal with sulfur

Example 1: Elastic and Ultimate Tensile Stresses

(API Std 530)

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Example 2: Hoop Stress vs. Creep Life

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Example 3: High Temperature Hydrogen Attack

Nelson Curves (API RP 941)

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Example 4: Chloride Stress Corrosion Cracking

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Pinhole Leaks

Bushings

Spacer

Leaks in APTAC Magnedrive housing (Fall 2007 DIERS UG Presentation)

Examination – Pits Found on the ID of APTAC Magnedrive Housing – Chloride SCC

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Example 5: Caustic Stress Corrosion Cracking Refinery Example – Caustic Wash Tower• Post-weld Heat

Treatment not done (temperature <150°F)

• Process upset 200°F

• Every weld in the tower cracked

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Failure Mechanism Temperature Regimes

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Considerations

• Will the vessel become permanently deformed or fail catastrophically? Some key mechanical properties, such as modulus of elasticity, yield strength, and tensile strength, reduce at higher temperatures.

• Will the vessel material be subjected to creep damage? See API 530

• Will the vessel see any other damage (accelerated corrosion, environmental cracking, ...etc.)? A materials/corrosion specialist should be consulted on a case-by- case basis. API 571 is very helpful and informative. 28

References• API RP 571 (Dec. 2003) – Damage Mechanisms

Affecting Fixed Equipment in the Refining Industry

• API Std 579 (June 2007) – Fitness-for-Service

• API Std 530 (Sep. 2008) – Calculation of Heater Tube Thickness in Petroleum Refineries

• API RP 941 (Aug. 2008) – Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants

• ASME Section II (July 2007) – Boiler and Pressure Vessel Code – Materials

• ASME Section VIII ( ) – Boiler and Pressure Vessel Code – Rules for Construction of Pressure Vessels

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Summary: High Temperature Effects on Vessel Integrity

• When evaluating the impact of high temperature, note that there are many failure mechanisms that could be relevant

• Mechanical strength (plastic deformation) is only one aspect of vessel integrity

• Consult a pressure equipment integrity expert (mechanical/metallurgical/corrosion) to evaluate the effect of high temperature on a vessel

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