API571 QUESTIONS

© Matthews Engineering Training LtdSlide 1

API 510 CERT

API RP 571

DAMAGE MECHANISMS AFFECTING FIXED

EQUIPMENT IN THE REFINING INDUSTRY

This is an API RP document (Recommended practice)

Still on the first edition:2003


API 510 CERT

API RP 571

DAMAGE MECHANISMS AFFECTING FIXED

EQUIPMENT IN THE REFINING INDUSTRY

Note it specifically relates to fixed

equipment such as pipes,vessels and

exchangers(i.e. not rotating

equipment such as pumps)

Similar to API 578 (material

verification), API 571 is an

‘afterthought’ document,recently

introduced into the API syllabus to

replace obsolete ‘IRE’ documents that

covered similar subjects


API 510 CERT API RP 571

Note how this general terminology of damage mechanism

covers more than just corrosion mechanisms

API 571 is basically an information book

containing technical descriptions of

damage mechanisms

Damage mechanisms

Corrosion

mechanisms

Other

mechanisms


API 510 CERT

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


API 510 CERTAPI 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


















Notice how these 15 damage mechanisms cover

several different applications:

These are

boiler/high-

temperature process

mechanisms


















We will deviate from the order of API 571 and look at

these in slightly more logical groupings:

This PowerPoint presentation will

look at these 4 as the first group of damaged mechanisms covered by

API 571

















API 510 CERT

API 571 COVERAGE OF THE DAMAGE

MECHANISMS

Description/appearance

of the

damage mechanism

Critical

factorsAffected

equipmentPrevention/

mitigation

Inspection/

monitoring

Related

mechanisms

API 571 looks at each of the damage mechanisms in this way:

Have a look at the

sections of API 571

and you will see this

pattern


API 510 CERTBRITTLE FRACTURE

It’s a failure mechanism…not a corrosion mechanism,as such

Sudden fracture of the material without

any plastic deformation

Flat

fracture

face

Cracks tend to

be straight


API 510 CERTBRITTLE 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


API 510 CERT

BRITTLE FRACTURE

Vulnerable materials

400

Plain carbon steels

Low alloy steels(1-2%Cr

etc)

400-series stainless steels


API 510 CERTTEMPER EMBRITTLEMENT

This is a specific type of brittle fracture failure…a different

cause and different effect to the ‘low temperature’ type

THE CAUSE IS:

THE EFFECT IS

Prolonged exposure to

temperatures

342-593 degC (650-1100 degF).

Reduction in toughness(impact strength)

during start-up and shutdown (rather than

at operating temperature) leading to brittle

fracture



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



NOTE THESE POINTS ON TEMPERATURE RANGE

342 degC 593 degC

482degC440degC

The general susceptibility range

Range for 2 ¼ Cr-1Mo

Temper embrittlement develops

more quickly at 482 degC

But the damage is more

severe after prolonged

exposure at 440 degC BUT



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-to-

brittle transition temperature

Read the other technical details in

API 571 4.2.3.6NOW


API 510 CERTTHERMAL FATIGUE

The result of cyclic stresses caused by temperature variations

Variations of more than about 93

degC (200 degF) can cause

thermal fatigue

Rule of thumbCracks lead to

failure


API 510 CERTTHERMAL FATIGUE

On a macro scale,cracks

tend to be dagger-shaped

,wide and oxide-

filled(caused by the

oxidising effect of the

temperature variations)

Here,joint restraint

has caused excessive

thermal stresses to

occur


API 510 CERT

MECHANICAL FATIGUE

The result of cyclic stresses caused by mechanical loadings

Common around stress

concentrations

•Changes of section

•Keyways

•Rough welds

•Thread notches

Fatigue crack in progress Propagation to failure


API 510 CERTENDURANCE LIMIT

(sometimes called Fatigue limit)

Stress

amplitude S

Number of cycles N

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

Many other materials e.g

300/400 stainless steels,and

aluminium DO NOT have

an endurance limit

BUT


API 510 CERTENDURANCE LIMIT

Stress

S

Cycles N

For materials that do have

an endurance limit:

Rule of thumb

The limit is about 40-

50% of UTS:

UTS


API 510 CERT

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’


API 510 CERT

VIBRATION-INDUCED FATIGUE

This is simply mechanical fatigue caused by induced vibrations

•Water hammer

•‘Flash-off’ of fluid

•Small-bore pipes that are unsupported

•Vortex-vibration in heat exchangers

•Failure of pipe hangers

Typical causes:

Failures commonly occur at

socket welded or threaded joints:

Like these:


API 510 CERT

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

API571 QUESTIONS

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