Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

API 571 2nd Ed > Mechanical and Metallurgical Failure Mechanisms > Flashcards

Mechanical and Metallurgical Failure Mechanisms Flashcards

1
Q

____ is a change in the microstructure of certain carbon steels and 0.5Mo steels after longterm
operation in the 800°F to 1100°F (427°C to 593°C) range that may cause a loss in strength,
ductility, and/or creep resistance

A

Graphitization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What materials are affected by Graphitization?

A

Some grades of carbon steel and 0.5Mo steels.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the most important factors that affect graphitization?

A

chemistry, stress, temperature, and time

of exposure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What equipment is affected by graphitization?

A

Primarily hot-wall piping and equipment in the FCC, catalytic reforming and coker units

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What metalurgies can be used to prevent Graphitization?

A

chromium containing low alloy steels for long-term operation

above 800°F (427°C).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How do you inspect for graphitization?

A

Evidence of graphitization is most effectively evaluated through removal of full thickness samples for
examination using metallographic techniques. Damage may occur midwall so that field replicas may
be inadequate.

Advanced stages of damage related to loss in strength include surface breaking cracks or creep
deformation that may be difficult to detect.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

_________ is a change in the microstructure of steels after exposure in the 850°F to 1400°F (440°C
to 760°C) range, where the carbide phases in carbon steels are unstable and may agglomerate from their
normal plate-like form to a spheroidal form, or from small, finely dispersed carbides in low alloy steels like
1Cr-0.5Mo to large agglomerated carbides

A

Softening (Spheroidization)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What materials are affected by Softening (Spheroidization)

A

All commonly used grades of carbon steel and low alloy steels including C-0.5Mo, 1Cr-0.5Mo,1.25Cr-
0.5Mo, 2.25Cr-1Mo, 3Cr-1Mo, 5Cr-0.5Mo, and 9Cr-1Mo steels.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the critical factors for Spheroidization?

A

Metal chemistry, microstructure, exposure time, and temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What equipment is affected by Spheroidization?

A

it an occur in piping and equipment after exposure to temperatures above 850°F
(454°C)
it also affects hot wall piping and equipment in the FCC, catalytic reforming and coker
units. Fired heater tubes in boilers or process units may be affected by a loss in creep strength.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How do you prevent Spheroidization?

A

by minimizing long-term exposure to elevated temperatures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

__________ is the reduction in toughness due to a metallurgical change that can occur in some
low alloy steels as a result of long term exposure in the temperature range of about 650°F to 1070°F
(343°C to 577°C).

A

Temper Embrittlement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What materials are affected the most by Temper Embritlement

A

Primarily 2.25Cr-1Mo low alloy steel, 3Cr-1Mo (to a lesser extent), and the high-strength low alloy
Cr-Mo-V rotor steels.

2.25Cr-1Mo materials manufactured prior to 1972 may be particularly susceptible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the critical factors of Temper Embritlement?

A

Alloy steel composition, thermal history, metal temperature and exposure time are critical factors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What Equipment is affected by Temper Embritlement?

A

hydroprocessing units,
particularly reactors, hot feed/effluent exchanger components, and hot HP separators

Temper embrittlement occurs in a variety of process units after long term exposure to temperatures
above 650°F (343°C). It should be noted that there have been very few industry failures related
directly to temper embrittlement.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How can you prevent Temper Embritlement for equipment exposed to the critical temperature range?

A

Temper embrittlement cannot be prevented if the material contains critical levels of the
embrittling impurity elements and is exposed in the embrittling temperature range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How do you inspect for Temper Embritlement?

A

install blocks of original heats of the alloy steel material inside
the reactor.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

__________ is a form of damage found mostly in older vintage carbon steels and C-0.5 Mo low alloy
steels under the combined effects of deformation and aging at an intermediate temperature.

A

Strain Aging

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is affected by Strain Aging

A

Mostly older (pre-1980’s) carbon steels with a large grain size and C-0.5 Mo low alloy steel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

_________ is a loss in toughness due to a metallurgical change that can occur in alloys
containing a ferrite phase, as a result of exposure in the temperature range 600°F to 1000°F (316°C to
540°C).

A

885°F (475°C) Embrittlement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What materials are affected by 885 Embrittlement?

A

a) 400 Series SS (e.g., 405, 409, 410, 410S, 430 and 446).

b) Duplex stainless steels such as Alloys 2205, 2304 and 2507.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the critical factors for 885 Embrittlement?

A

The alloy composition, particularly chromium content, amount of ferrite phase, and operating
temperature are critical factors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How long does it take for 885 Embrittlement to occur?

A

Since 885°F embrittlement can occur in a relatively short period of time, it is often assumed that
susceptible materials that have been exposed to temperatures in the 700°F to 1000°F (371°C to
538°C) range are affected

24
Q

How do you inspect for 885 Embrittlement?

A

Impact or bend testing of samples removed from service is the most positive indicator of a problem.
b) Most cases of embrittlement are found in the form of cracking during turnarounds, or during startup
or shutdown when the material is below about 200°F (93°C) and the effects of embrittlement are
most detrimental.
c) An increase in hardness is another method of evaluating 885°F embrittlement.

25
Q

Formation of a metallurgical phase known as _______ can result in a loss of fracture toughness in
some stainless steels as a result of high temperature exposure.

A

Sigma Phase

26
Q

What materials are affected by Sigma Phase Embrittlemnt?

A

a) 300 Series SS wrought metals, weld metal, and castings. Cast 300 Series SS including the HK and
HP alloys are especially susceptible to sigma formation because of their high (10% to 40%) ferrite
content.
b) The 400 Series SS and other ferritic and martensitic SS with 17% Cr or more are also susceptible
(e.g., Types 430 and 440).
c) Duplex stainless steels.

27
Q

What are the critical factors of Sigma Phase Embrittlement?

A

Alloy composition, time and temperature are the critical factors.

28
Q

What equipment is affected by Sigma Phase?

A

a) Common examples include stainless steel cyclones, piping ductwork and valves in high temperature
FCC Regenerator service.
b) 300 Series SS weld overlays and tube-to-tubesheet attachment welds can be embrittled during
PWHT treatment of the underlying CrMo base metal.
c) Stainless steel heater tubes are susceptible and can be embrittled.

29
Q

Is Sigma Phase readily apparent upon inspection?

A

No,
Sigma phase embrittlement is a metallurgical change that is not readily apparent, and can only be
confirmed through metallographic examination and impact testing. (Tables 4-1 and 4-2)
b) Damage due to sigma phase embrittlement appears in the form of cracking, particularly at welds or
in areas of high restraint.

30
Q

How do you prevent Sigma Phase?

A

The best way to prevent sigma phase embrittlement is to use alloys that are resistant to sigma
formation or to avoid exposing the material to the embrittling range.

31
Q

How do you inspect for Sigma Phase?

A

Physical testing of samples removed from service is the most positive indicator of a problem.
b) Most cases of embrittlement are found in the form of cracking in both wrought and cast (welded)
metals during turnarounds, or during startup or shutdown when the material is below about 500°F
(260°C) and the effects of embrittlement are most pronounced.

32
Q

__________ is the sudden rapid fracture under stress (residual or applied) where the material exhibits
little or no evidence of ductility or plastic deformation.

A

Brittle Fracture

33
Q

What materials are affected by Brittle Fracture?

A

Carbon steels and low alloy steels are of prime concern, particularly older steels. 400 Series SS are also
susceptible.

34
Q

What are the critical factors for Brittle Fracture?

A

For a material containing a flaw, brittle fracture can occur. Following are three important factors:
1) The Material fracture toughness (resistance to crack like flaws) as measured in a Charpy
impact test;
2) The size, shape and stress concentration effect of a flaw;
3) The amount of residual and applied stresses on the flaw.

35
Q

When does Brittle Fracture most likely occur?

A

In most cases, brittle fracture occurs only at temperatures below the Charpy impact transition
temperature (or ductile-to-brittle transition temperature), the point at which the toughness of the
material drops off sharply.

36
Q

What equipment is affected by Brittle Fracture?

A

Equipment manufactured to the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1,
prior to the December 1987 Addenda, were made with limited restrictions on notch toughness for
vessels operating at cold temperatures.

37
Q

When is equipment manufactured after 1987 Addenda susceptible to Brittle Fracture?

A

Equipment made to the same code after this date were subject to the requirements of UCS 66
(impact exemption curves).

38
Q

When is Brittle Fracture most likely to occur?

A

Most processes run at elevated temperature so the main concern is for brittle fracture during startup,
shutdown, or hydrotest/tightness testing. Thick wall equipment on any unit should be considered.

39
Q

What does Brittle Fracture look like?

A

Cracks will typically be straight, non-branching, and largely devoid of any associated plastic
deformation

40
Q

What prevents Brittle Fracture?

A

For new equipment, brittle fracture is best prevented by using materials specifically designed for low
temperature operation including upset and autorefrigeration events.

41
Q

What type of Damage Mechanism is Brittle Fracture?

A

Brittle fracture is an “event” driven damage mechanism.

42
Q

What type of inspection can help mitigate Brittle Fracture?

A

a) Inspection is not normally used to mitigate brittle fracture.
b) Susceptible vessels should be inspected for pre-existing flaws/defects.

43
Q

At high temperatures, metal components can slowly and continuously deform under load below the
yield stress. This time dependent deformation of stressed components is known as ________.

A

Creep

44
Q

____________ is the result of cyclic stresses caused by variations in temperature. Damage is in the
form of cracking that may occur anywhere in a metallic component where relative movement or
differential expansion is constrained, particularly under repeated thermal cycling.

A

Thermal fatigue

45
Q

Permanent deformation occurring at relatively low stress levels as a result of localized overheating. This
usually results in bulging and eventually failure by ____________

A

Stress rupture

46
Q

Describe Steam Blanketing.

A

The flow of heat energy
through the wall of the tube results in the formation of discrete steam bubbles (nucleate boiling) on the ID
surface. The moving fluid sweeps the bubbles away. When the heat flow balance is disturbed, individual
bubbles join to form a steam blanket, a condition known as Departure From Nucleate Boiling (DNB).
Once a steam blanket forms, tube rupture can occur rapidly, as a result of short term overheating, usually
within a few minutes.

47
Q

What can occur if dissimilar metals are welded together.

A

Dissimilar Metal Weld (DMW) Cracking

48
Q

A form of thermal fatigue cracking – _________– can occur when high and non-uniform thermal stresses develop over a relatively short time in a piece of equipment due to differential expansion or
contraction. If the thermal expansion/contraction is restrained, stresses above the yield strength of the
material can result. ____________ usually occurs when a colder liquid contacts a warmer metal surface.

A

Thermal shock

49
Q

_____ is the accelerated mechanical removal of surface material as a result of relative movement
between, or impact from solids, liquids, vapor or any combination thereof.

A

Erosion

50
Q

______ is a description for the damage that occurs when corrosion contributes to erosion
by removing protective films or scales, or by exposing the metal surface to further corrosion under
the combined action of erosion and corrosion.

A

Erosion-corrosion

51
Q

What material is affected by Erosion - Corrosion?

A

All metals, alloys and refractories

52
Q

What are the critical factors of Erosion-Corrosion?

A

In most cases, corrosion plays some role so that pure erosion (sometimes referred to as abrasive
wear) is rare. It is critical to consider the role that corrosion contributes.

Softer the metal the more susceptible it is to Erosion

53
Q

What equipment is affected by Erosion-Corrosion?

A

All types of equipment exposed to moving fluids and/or catalyst are subject to erosion and erosioncorrosion.
This includes piping systems, particularly the bends, elbows, tees and reducers; piping
systems downstream of letdown valves and block valves; pumps; blowers; propellers; impellers;
agitators; agitated vessels; heat exchanger tubing; measuring device orifices; turbine blades;
nozzles; ducts and vapor lines; scrapers; cutters; and wear plates.

54
Q

________ is characterized by a localized loss in thickness in the form of pits,
grooves, gullies, waves, rounded holes and valleys. These losses often exhibit a directional pattern.

A

Erosion Corrosion

55
Q

How do you prevent Erosion Corrosion?

A

Improvements in design involve changes in shape, geometry and materials selection. Some
examples are: increasing the pipe diameter to decrease velocity; streamlining bends to reduce
impingement; increasing the wall thickness; and using replaceable impingement baffles

56
Q

How do you inspect for Erosion-Corrosion?

A

a) Visual examination of suspected or troublesome areas, as well as UT checks or RT can be used to
detect the extent of metal loss.
b) Specialized corrosion coupons and on-line corrosion monitoring electrical resistance probes have
been used in some applications.
c) IR scans are used to detect refractory loss on stream.

57
Q

_______ is a form of erosion caused by the formation and instantaneous collapse of innumerable
tiny vapor bubbles.

A

Cavitation

API 571 2nd Ed (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions