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API RP 571 DAMAGE MECHA MECHANISMS NISMS AFFECT AFFECTING ING FIXED EQUIPMENT EQUIPME NT IN THE THE REFINING REFINING INDUSTRY INDUSTRY

This is an API RP document (Recommended practice) Still on the first edition:2003 © Mat Matthew thewss Engine Engineeri ering ng Train Training ing Ltd Ltd

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API RP 571

DAMAGE MECHA MECHANISMS NISMS AFFECT AFFECTING ING FIXED EQUIPMENT EQUIPME NT IN THE THE REFINING REFINING INDUSTRY INDUSTRY

Note it specifically specifically relates to fixed fixed equipment such as pipes,vessels and exchangers(i.e.. not rotating exchangers(i.e equipment such as pumps)

Similar to API 578 (material verification),, API 571 is an verification) ‘afterthou ‘afte rthought’ ght’ docum document,r ent,rece ecently ntly introduced into the API syllabus to replace repla ce obsole obsolete te ‘IRE ‘IRE’’ docu documen ments ts that covered similar subjects

© Mat Matthew thewss Engine Engineeri ering ng Train Training ing Ltd Ltd

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API 510 CERT

API RP 571

API 571 is basically an information book containing technical descriptions of

damage mechanisms Note how this general terminology of damage mechanism covers more than just corrosion mechanisms

Damage mechanisms Corrosion mechanisms © Matthews Engineering Training Ltd

Other mechanisms Slide 3

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4.2.3 – Temper Embrittlement 4.2.7 – Brittle Fracture 4.2.9 – Thermal Fatigue 4.2.14 – Erosion/Erosion-Corrosion 4.2.16 – Mechanical Fatigue 4.3.2 – Atmospheric Corrosion 4.3.3 – Corrosion Under Insulation (CUI) 4.3.4 – Cooling Water Corrosion 4.3.5 – Boiler Water Condensate Corrosion 4.4.2 – Sulfidation 4.5.1 – Chloride Stress Corrosion Cracking (Cl-SCC) 4.5.2 – Corrosion Fatigue 4.5.3 – Caustic Stress Corrosion Cracking (Caustic Embrittlement) 5.1.2.3 – Wet H2S Damage (Blistering/HIC/SOHIC/SCC) 5.1.3.1 – High Temperature Hydrogen Attack (HTHA

© Matthews Engineering Training Ltd

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API 510 CERT

API RP 571:CONTENTS

The API 510 syllabus does not include all of API 571,only some of it…15 damage mechanisms

The contents of API 571

API 510 syllabus sections

4.2.3 – Temper Embrittlement 4.2.7 – Brittle Fracture 4.2.9 – Thermal Fatigue 4.2.14 – Erosion/Erosion-Corrosion 4.2.16 – Mechanical Fatigue 4.3.2 – Atmospheric Corrosion 4.3.3 – Corrosion Under Insulation (CUI) 4.3.4 – Cooling Water Corrosion 4.3.5 – Boiler Water Condensate Corrosion 4.4.2 – Sulfidation 4.5.1 – Chloride Stress Corrosion Cracking (Cl-SCC) 4.5.2 – Corrosion Fatigue 4.5.3 – Caustic Stress Corrosion Cracking (Caustic Embrittlement) 5.1.2.3 – Wet H2S Damage (Blistering/HIC/SOHIC/SCC) 5.1.3.1 – High Temperature Hydrogen Attack (HTHA


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API 510 CERT

API RP 571:CONTENTS

Notice how these 15 damage mechanisms cover several different applications: 4.2.3 – Temper Embrittlement 4.2.7 – Brittle Fracture 4.2.9 – Thermal Fatigue 4.2.14 – Erosion/Erosion-Corrosion 4.2.16 – Mechanical Fatigue 4.3.2 – Atmospheric Corrosion 4.3.3 – Corrosion Under Insulation (CUI) 4.3.4 – Cooling Water Corrosion 4.3.5 – Boiler Water Condensate Corrosion 4.4.2 – Sulfidation 4.5.1 – Chloride Stress Corrosion Cracking (Cl-SCC) 4.5.2 – Corrosion Fatigue 4.5.3 – Caustic Stress Corrosion Cracking (Caustic Embrittlement) 5.1.2.3 – Wet H2S Damage (Blistering/HIC/SOHIC/SCC) 5.1.3.1 – High Temperature Hydrogen Attack (HTHA


These are boiler/hightemperature process mechanisms

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API 510 CERT

API RP 571:CONTENTS

We will deviate from the order of API 571 and look at these in slightly more logical groupings:

4.2.3 – Temper Embrittlement This PowerPoint presentation will 4.2.7 – Brittle Fracture 4.2.9 – Thermal Fatigue as the first group of look at these 4.2.14 – Erosion/Erosion-Corrosion 4.2.16 – Mechanical Fatigue damaged mechanisms covered by 4.3.2 – Atmospheric Corrosion API 571 4.3.3 – Corrosion Under Insulation (CUI) 4.3.4 – Cooling Water Corrosion 4.3.5 – Boiler Water Condensate Corrosion 4.4.2 – Sulfidation 4.5.1 – Chloride Stress Corrosion Cracking (Cl-SCC) 4.5.2 – Corrosion Fatigue 4.5.3 – Caustic Stress Corrosion Cracking (Caustic Embrittlement) 5.1.2.3 – Wet H2S Damage (Blistering/HIC/SOHIC/SCC) 5.1.3.1 – High Temperature Hydrogen Attack (HTHA

4


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API 571 COVERAGE OF THE DAMAGE MECHANISMS API 571 looks at each of the damage mechanisms in this way:

Description/appearance of the damage mechanism

Have a look at the sections of API 571 and you will see this pattern

Critical factors

Affected equipment Prevention/ mitigation

Related mechanisms

Inspection/ monitoring


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BRITTLE FRACTURE

It’s a failure mechanism…not a corrosion mechanism,as such Flat fracture face Cracks tend to be straight Sudden fracture of the material without any plastic deformation


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BRITTLE FRACTURE

Caused by hydro-testing and/or operating below the Charpy impact transition temperature

Low temperature during pressure test =Low ductility =Low impact strength = Failure


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BRITTLE FRACTURE Vulnerable materials Plain carbon steels

400-series stainless steels

400

Low alloy steels(1-2%Cr etc) © Matthews Engineering Training Ltd

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TEMPER EMBRITTLEMENT

This is a specific type of brittle fracture failure…a different cause and different effect to the ‘low temperature’ type Prolonged exposure to THE CAUSE IS: temperatures 342-593 degC (650-1100 degF).

THE EFFECT IS

Reduction in toughness(impact strength) during start-up and shutdown (rather than at operating temperature) leading to brittle fracture © Matthews Engineering Training Ltd

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TEMPER EMBRITTLEMENT Its an alloy-specific damage mechanism

AFFECTED MATERIALS:

2 ¼ Cr –Mo low alloy steels and similar.Used in boilers,refinery reactors,cat crackers,cokers etc

The susceptibility to temper embrittlement is a function of trace element composition:Manganese,Silicon, and trace elements P,Sn etc


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NOTE THESE POINTS ON TEMPERATURE RANGE 342 degC

The general susceptibility range

593 degC

Range for 2 ¼ Cr-1Mo 440degC

But the damage is more severe after prolonged exposure at 440 degC

482degC

BUT

Temper embrittlement develops more quickly at 482 degC


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The effect is an increase in the temperature at which the material becomes brittle

API 571 describes this as: an upward shift in the ductile-tobrittle transition temperature

NOW

Read the other technical details in API 571 4.2.3.6


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THERMAL FATIGUE

The result of cyclic stresses caused by temperature variations

Cracks lead to failure

Rule of thumb

Variations of more than about 93 degC (200 degF) can cause thermal fatigue © Matthews Engineering Training Ltd

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THERMAL FATIGUE

Here, joint restraint has caused excessive thermal stresses to occur

On a macro scale,cracks tend to be dagger-shaped ,wide and oxidefilled(caused by the oxidising effect of the temperature variations) © Matthews Engineering Training Ltd

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MECHANICAL FATIGUE The result of cyclic stresses caused by mechanical loadings

Common around stress concentrations

Fatigue crack in progress

•Changes of section •Keyways •Rough welds •Thread notches

Propagation to failure


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ENDURANCE LIMIT (sometimes called Fatigue limit)

Stress amplitude S Below this stress, the material will not suffer fatigue cracking ,no matter how many stress cycles it sees

•Plain Carbon steels •Low alloy steels •Titanium

DO have an endurance limit

Number of cycles N

BUT

Many other materials e.g 300/400 stainless steels,and aluminium DO NOT have an endurance limit


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ENDURANCE LIMIT

Rule of thumb

For materials that do have an endurance limit:

The limit is about 4050% of UTS:

Stress S

UTS

Cycles N © Matthews Engineering Training Ltd

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MECHANICAL FATIGUE Mechanical fatigue failure is characterised by ‘Beach Marks’ resulting from progressive propagation and arrest of the crack

API 571 prefers to call multiple initiation points and beach marks a ‘clam shell fingerprint’


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VIBRATION-INDUCED FATIGUE This is simply mechanical fatigue caused by induced vibrations

Typical causes:

Failures commonly occur at socket welded or threaded joints:

•Water hammer •‘Flash-off’ of fluid •Small-bore pipes that are unsupported •Vortex-vibration in heat exchangers •Failure of pipe hangers

Like these:


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BEFORE PROCEEDING FURTHER…… Check now that you understand the difference between brittle fracture and fatigue. Have a look in your copy of API 571 at the mechanisms covered in this presentation and read the ‘affected materials’ and ‘Prevention/mitigation’ sections for each of these mechanisms After that , return to the module text itself and we’ll look at some more of the damage mechanisms that are described in API 571

571 © Matthews Engineering Training Ltd

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API571 QUESTIONS

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