ch6- API 571.pdf

Chapter 6 API 571 6.1 6. 1

APII 57 AP 571: 1: In Intr trod oduc ucti tion on

This chapter covers the contents of API 571:   Damage mechanisms affecting fixed equipment in the refining industry: 2003.. API 571 has only recently been added to the syllabus 2003 forr th fo thee AP APII 57 570 0 an and d 51 510 0 ex exam amin inat atio ions ns an and d re repl plac aces es wh what at used to be included in an old group of documents dating fro rom m th thee 19 196 60s en enti titl tled ed IR IRE E (In Insp spec ecti tion on of re refin finer ery y equ equip ip-ment). ment ). The first point to note is that the API 571 sections covered in the API 570 ICP exam syllabus is only an extract from the full version of API 571.

6.1.1 Th 6.1.1 The e fift fifteen een da dama mage ge me mech chan anism isms s Your copy of API 571 contains (among other things) descriptions of fifteen damage mechanisms (we will refer to them as DMs). Here they are in Fig. 6.1. Remember that these are all DMs that are found in the

1. Br Brit ittl tle e fr frac actu ture re 2. Th Ther erma mall fa fati tigu gue e 3. Ero Erosio sion–c n–corr orros osion ion 4. Me Mech chan anic ical al fa fati tigu gue e 5. Vib Vibrat ration ion-in -indu duced ced fat fatigu igue e 6. Atm Atmosp ospher heric ic cor corros rosion ion 7. Cor Corros rosion ion unde underr insula insulatio tion n (CUI) (CUI) 8. Boi Boiler ler con conden densat sate e corr corrosi osion on 9. Flu Flue-g e-gas as dewp dewpoin ointt corro corrosio sion n 10. Microbiological-induced corrosion (MIC) 11. Soil corrosion 12. Sulfidation 13. SCC 14. Caustic embrittlement 15. High-temperature hydrogen attack (HTHA) Figure Fig ure 6.1

Fiftee Fif teen n API API 571 dam damage age mec mechan hanis isms ms WPASME100609

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petroch petr ochem emic ical al/r /refi efini ning ng in indus dustr try y (b (bec ecau ause se th that at is wh what at AP APII 571 is about), but they may or may not be found in other indu in dust stri ries es.. So Some me,, su such ch as br brit ittl tlee fr frac actu ture re an and d fa fati tigu gue, e, ar aree commonly found in non-refinery plant whearas others, such as sulfidation, are not.

6.1.2 Ar 6.1.2 Are e these these DMs DMs in in some some kind kind of preci precise se logi logica call order? No, or if they are, it is difficult to see what it is. The list contains a mixture of high- and low-temperature DMs, some of which affect plain carbon stee eells mor oree than alloy or stainless steels and vice versa. There are also various subd su bdiv ivis isio ions ns an and d a bi bitt of re repe peti titi tion on thr hrow own n in fo forr go good od measure. None of this is worth worrying about, as the order in which they appear is not important. In order to make the DMs easier to remember you can think of them as being separated into three groups. There is no code significance in this rearrangement at all; it is simply to ma make ke th them em ea easi sier er to re reme mem mbe ber. r. Fi Figu gure re 6. 6.2 2 sh show owss th thee

Figu Fi gure re 6. 6.2 2

DMs: DM s: a revi revise sed d ord order  er 

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revised order in which they appear in the familiarization questions. One important feature of API 571 is that it describes each DM in some detail, with the text for each one subdivided into six subsections. Figure 6.3 shows the subsections and the order in which they appear. These six subsections are   important   as they form the subject matter from which the API examination questions are taken. As there are no calculations in API 571, and only a few graphs, etc., of detailed information, you can expect most of the API examination questions to be closed book, i.e.

Figure 6.3

The content ’subsections’ of API 571 WPASME100609

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a test of your understanding and short-term memory of the DMs. The questions could come from any of the six subsections shown in Fig. 6.3.

6.2

The first group of DMs

The following Figs 6.4 to 6.7 relate to the first group of DMs in API 571. When looking through these figures, try to crossreference them to the content of the relevant sections of API 571. Then read the full sections of API 571 covering the four DMs in this first group.

Figure 6.4

Brittle facture

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Figure 6.5

Figure 6.6

Thermal fatigue

Mechanical fatigue

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Figure 6.7

6.3

Vibration-induced fatigue

API 571 familiarization questions (set 1)

Attempt this first set of self-test questions covering the first group of API 571 DMs.

Q1.

API 571 section 4.2.7.1: brittle fracture

Which of these is a description of brittle fracture? (a) Sudden rapid fracture of a material with plastic deformation (b) Sudden rapid fracture of a material without plastic deformation (c) Unexpected failure as a result of cyclic stress (d) Fracture caused by reaction with sulfur compounds

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Q2. API 571 section 4.2.7.2: brittle fracture: affected materials Which of these materials are particularly susceptible to brittle fracture? (a) Plain carbon and high alloy steels (b) Plain carbon, low alloy and 300 series stainless steels (c) Plain carbon, low alloy and 400 series stainless steels (d) High-temperature resistant steels

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Q3. API 571 section 4.2.7.3: brittle fracture: critical factors At what temperature is brittle fracture most likely to occur? (a) Temperatures above 400 C (b) Temperatures above the Charpy impact transition temperature (c) Temperatures below the Charpy impact transition temperature (d) In the range 20–110 C 8

8

Q4.

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API 571 section 4.2.7.4: brittle fracture

Which of these activities is   unlikely   to result in a high risk of  brittle fracture? (a) Repeated hydrotesting above the Charpy impact transition temperature (b) Initial hydrotesting at low ambient temperatures (c) Start-up of thick-walled vessels (d) Autorefrigeration events

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Q5. API 571 section 4.2.7.6: brittle fracture: prevention/mitigation What type of material change will   reduce   the risk of brittle fracture? (a) Use a material with lower toughness (b) Use a material with lower impact strength (c) Use a material with a higher ductility (d) Use a thicker material section

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Q6. API 571 section 4.2.7.5: brittle fracture: appearance Cracks resulting from brittle fracture will most likely be predominantly: (a) (b) (c) (d)

Branched Straight and non-branching Intergranular Accompanied by localized necking around the crack

Q7.

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API 571 section 4.2.9: thermal fatigue: description

What is thermal fatigue? (a) The result of excessive temperatures (b) The result of temperature-induced corrosion

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(c) The result of cyclic stresses caused by temperature variations & (d) The result of cyclic stresses caused by dynamic loadings &

Q8. API 571 section 4.2.9.3: thermal fatigue: critical factors As a practical rule, thermal cracking may be caused by temperature swings of  approximately: (a) (b) (c) (d)

200 200 100 100

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C F C F

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Q9. API 571 section 4.2.9.5: thermal fatigue: appearance Cracks resulting from thermal fatigue will most likely be predominantly: (a) Straight and non-branching (b) Dagger-shaped (c) Intergranular (d) Straight and narrow

Q10.

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API 571 section 4.2.9.6: prevention/mitigation

Thermal fatigue cracking is best avoided by: (a) Better material selection (b) Control of design and operation (c) Better post-weld heat treatment (PWHT) (d) Reducing mechanical vibrations

6.4

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The second group of DMs

Figures 6.8 to 6.10 relate to the second group of DMs. Note how these DMs tend to be environment-related. Remember to identify the six separate subsections in the text for each DM.

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Figure 6.8

Figure 6.9

Erosion/corrosion

Corrosion under insulation (CUI)

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Figure 6.10

Soil corrosion

6.5

API 571 familiarization questions (set 2)

Q1.

API 571 section 4.2.14

A damage mechanism that is strongly influenced by fluid velocity and the corrosivity of the process fluid is known as: (a) Mechanical fatigue (b) Erosion–corrosion (c) Dewpoint corrosion (d) Boiler condensate corrosion

Q2.

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API 571 section 4.3.2: atmospheric corrosion

As a practical rule, atmospheric corrosion: (a) Only occurs under insulation (b) May be localized or general (widespread) (c) Is generally localized (d) Is generally widespread

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Q3. API 571 section 4.3.2.3: atmospheric corrosion: critical factors A typical atmospheric corrosion rate in mils (1 mil = 0.001 in) per year (mpy) of steel in an inland location with moderate precipitation and humidity is: (a) 1–3 mpy (b) 5–10 mpy (c) 10–20 mpy (d) 50–100 mpy

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Q4.

API 571 section 4.3.3.3: CUI critical factors

Which of these metal temperature ranges will result in the most severe CUI? (a) (b) (c) (d)

0–51 C 100–121 C 0 to 10 C 250+ C 8

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Q5.

API 571 section 4.3.3.6: CUI appearance

Which other corrosion mechanism often accompanies CUI in 300 series stainless steels? (a) HTHA (b) Erosion–corrosion (c) Dewpoint corrosion (d) SCC

Q6.

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API 571 section 4.3.3.6: CUI prevention/mitigation

Which of these would   significantly reduce the risk   of the occurrence of CUI on a 316 stainless steel pipework system fitted with standard mineral wool lagging? (a) Change the pipe material to a 304 stainless steel (b) Change to a calcium silicate lagging material (c) Shotblast the pipe surface and re-lag (d) Change to low-chloride lagging material

Q7.

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API 571 section 4.3.9: soil corrosion

What is the main parameter measured to assess the corrosivity of  a soil? (a) (b) (c) (d)

Acidity Alkalinity Density Resistivity

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Q8. API 571 section 4.3.9.5: soil corrosion: appearance What would you expect the result of soil corrosion to look like? (a) Branched and dagger-shaped cracks (b) Isolated, large and deep individual pits (c) Straight cracks (d) External corrosion with wall thinning and pitting

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Q9.

API 571 section 4.3.9.6: soil corrosion protection

Which of these would be used to   reduce   the amount of soil corrosion? (a) Caustic protection (b) Cathodic protection (c) Anodic protection (d) More post-weld heat treatment

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Q10. API 571 section 4.3.9.3: soil corrosion critical factors What effect does metal temperature have on the rate of soil corrosion? (a) None (b) The corrosion rate increases with temperature (c) The corrosion rate decreases with temperature (d) There will be minimum soil corrosion below 0 C 8

6.6

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The third group of DMs

Now look through Figs 6.11 to 6.16 covering the final group of seven DMs. These DMs tend to be either more common at higher temperatures or a little more specific to refinery equipment than those in the previous two groups. Again, remember to identify the six separate subsections in the text for each DM, trying to anticipate the type of  examination questions that could result from the content.

Figure 6.11

Oxygen pitting

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Figure 6.12

Microbial-induced corrosion (MIC)

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Figure 6.13

Sulfidation corrosion

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Figure 6.14

Stress corrosion cracking (SCC)

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Figure 6.15

Figure 6.16

Caustic embrittlement

High-temperature hydrogen attack (HTHA) WPASME100609

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6.7

API 571 familiarization questions (set 3)

Now try the final set of API 571 self-test questions, covering the third group of DMs.

Q1. API 571 section 4.3.5: boiler water condensate corrosion Which substance is the main cause of corrosion (common to several corrosion mechanisms) in a boiler water condensate system? (a) Hydrogen (b) Chlorine (c) Hydrazine (d) Oxygen

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Q2. API 571 section 4.3.5.5: boiler water condensate corrosion: appearance What does CO2  corrosion of pipe internals look like? (a) Smooth grooving of the pipe wall (b) Blisters (tubercles) on the pipe wall (c) Branched cracks in the pipe wall (d) Cup-shaped pits and a slimy surface on the pipe wall

Q3.

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API 571 section 4.3.7: dew-point corrosion

Dew-point corrosion in flue gas systems in caused by: (a) (b) (c) (d)

The presence of living organisms High temperatures Sulfur and chlorine compounds Ash, particulates and other non-combustibles

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Q4. API 571 section 4.3.7.3: dew-point corrosion: critical factors Dew-point corrosion in a system where the flue gas contains SO 2 and SO3  occurs at what metal temperatures? (a) Below 138 C (b) Any temperature above 138 C (c) 138–280 C (d) Only below 54 C 8

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Q5. API 571 section 4.3.8: microbiologically induced corrosion (MIC) What does MIC typically look like? (a) Uniform wall thinning with a ‘sparkling’ corroded surface (b) Localized pitting under deposits (c) Smooth longitudinal grooving (d) A dry flaky appearance

Q6.

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API 571 section 4.4.2: sulfidation: critical factors

Sulfidation is the reaction of steels with sulfur compounds at what temperatures? (a) (b) (c) (d)

Any temperature 54–260 C Above 260 C Above 380 C

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Q7. API 571 section 4.4.2.4: sulfidation: affected equipment Which of these items of equipment would be most likely to suffer from sulfidation? (a) Natural gas-fired power boilers (b) Residual oil-fired boilers (c) High-pressure compressed air systems (d) Sea water cooling systems

Q8.

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API 571 section 4.4.2: sulfidation

Which curves document the effect of temperature on sulfidation rates in steels? (a) The NACE economy curves (b) The McConomy curves (c) The Larsen–Miller curves (d) The morphology curves

Q9.

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API 571 section 4.4.2: sulfidation

Which of these materials has the highest resistance to sulfidation? (a) Low carbon steel (b) 214 %  Cr alloy steel (c) 9 %  Cr alloy steel (d) 18/8 stainless steel

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Q10. API 571 section 4.5: environment-assisted cracking According to API, what are the two main types of environmentassisted cracking? (a) Chloride SCC and CUI (b) Chloride SCC and sulfur SCC (c) Chloride SCC and hydrogen attack (d) Chloride SCC and caustic embrittlement

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