571 - P1 (50Q) Flashcards
Sudden rapid fracture under stress (residual or applied) where the material exhibits little
or no evidence of ductility or plastic deformation is called
brittle fracture
Material affected by brittle fracture includes ____, _____ and ________.
carbon steel, low alloy steel and 400 series stainless steel.
The three factors leading to brittle fracture are
fracture toughness, flaw size and residual stress.
In most cases, brittle fracture occurs only at temperatures below the ________, the point at which the toughness of the material
drops off sharply
Charpy impact transition
temperature (or ductile-to-brittle transition temperature)
Most processes run at elevated temperature so the main concern is for brittle fracture during __________. Thick wall equipment on any unit should be considered
startup, shutdown, or hydrotest/tightness testing
Brittle fracture cracks are typically be ________, and largely devoid of any associated plastic deformation
(no shear lip or localized necking around the crack)
straight, non-branching
Microscopically, the brittle fracture crack surface will be composed largely of ____________ and very little microvoid coalescence.
cleveage, with limited intergranular cracking
For new equipment, brittle fracture is best prevented by using materials specifically designed for _________ operation including upset and autorefrigeration events.
low temperature
Performing a ________ on the vessel if it was not originally done during manufacturing may reduce likelihood of brittle fracture.
post weld heat treatment (PWHT)
A _______ followed by a lower temperature hydrotest to extend the Minimum Safe Operating Temperature (MSOT) envelope may be performed to reduce likelihood of brittle fracture.
“warm” pre-stress
Pressure vessel designed using ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, prior to
the ___________ Addenda may be affected by brittle fracture. The requirements of _______ (impact
exemption curves) was later introduced to avoid crack due to brittle fracture.
December 1987, UCS 66
________ is a mechanical form of degradation that occurs when a component is exposed to
cyclical stresses for an extended period, often resulting in sudden, unexpected failure.
Fatigue cracking
All engineering alloys are subject to fatigue cracking although the ________ and _________
necessary to cause failure vary by material
stress levels, number of cycles
Fatigue cracks usually initiate on the surface at notches or ________ under cyclic loading
stress raisers
Materials like austenitic stainless steels and
aluminum that do not have an endurance limit will have a fatigue limit defined by _________.
the number of cycles at a given stress amplitude
For alloys with endurance limits, _____ this limit, fatigue cracking will not occur, regardless of the number of cycles
below
The signature mark of a fatigue failure is a ________ type fingerprint that has concentric rings called
________ emanating from the crack initiation site
“clam shell”, “beach marks”
The best defense against fatigue cracking is ________.
good design
Surface preparation and ________ application are critical for long-term protection against atmospheric corrosion.
proper coating
Atmospheric corrosion rates increase with temperature up to about _________.
250oF (121oC)
Piping that rests on ________ is very prone to atmospheric corrosion due to _______ between the pipe and the support.
pipe supports, water entrapment
Corrosion under insulation becomes more severe at metal temperatures between the boiling point and _______, where water is less likely to vaporize and insulation stays wet longer
250oF (121oC)
_______ techniques for identifying wet insulation.
Neutron backscatter
CUI mitigation is best achieved by using appropriate __________ and maintaining the insulation /sealing /vapor barriers to prevent moisture ingress.
paints / coatings
Because there are several types of MIC, organisms can survive and grow under severe conditions including lack of oxygen, light or dark, high salinity, pH range of _____, and temperatures from ______.
0 to 12, 0oF to 235oF (–17 oC to 113oC)
MIC is most often found in heat exchangers, bottom water of storage tanks, piping with ________, and piping in contact with some soils.
stagnant or low flow
Damage is often characterized by ________ within pits in carbon steel or subsurface cavities in
stainless steel.
cup-shaped pits
To avoid MIC, systems that contain water (cooling water, storage tanks, etc.) should be treated with biocides such as ________ or proprietary compounds.
chlorine, bromine, ozone, ultraviolet light
Material affected by soil corrosion are ______.
Carbon steel, cast iron and ductile iron
The most common method used for monitoring underground structures is measuring the structure to
soil ____________ near the structure.
potential using dedicated reference electrodes
Material affected by caustic corrosion are primarily
carbon steel, low alloy steels and 300 Series SS.
Exposure to high solution strength caustic can result in general corrosion of carbon steel above ____ and very high corrosion rates above _____.
175oF (79oC), 200oF (93oC).
_______ gauging is useful to detect and monitor general corrosion due to caustic.
UT thickness
Material affected by ClSCC are
300 SS and Duplex SS
The greatest susceptibility to ClSCC is at a nickel
content of _____, highly resistance at ____ and immune above ____.
8% to 12% , 35%, 45%
Characteristic stress corrosion cracks have ______ and may be visually detectable by a _______ appearance of the surface
many branches, craze cracked
RT is ______ to detect cracks except in advanced stages where a significant network of cracks has developed.
not sufficiently sensitive
Caustic embrittlement is a form of stress corrosion cracking characterized by that ____________
occur in piping and equipment exposed to caustic, primarily adjacent to ______.
surface-initiated cracks, non-PWHT’d welds.
If a concentrating mechanism is present, caustic
concentrations of _______ are sufficient to cause cracking.
50 to 100 ppm
Caustic stress corrosion cracking typically propagates ______ to the weld in adjacent base metal but can
also occur in the weld deposit or heat-affected zones.
parallel
Cracking can be effectively prevented by means of a ________. A heat treatment at _______ is considered an effective stress relieving heat treatment for carbon
steel.
PWHT, 1150°F (621°C)
___ is not effective for finding tight, scale-filled cracks and should not be used for detection.
PT
Corrosion of steel due to acidic sour water containing H2S at a pH between ________. Carbon dioxide
(CO2) may also be present.
4.5 and 7.0
Sour water corrosion primarily affects _______
carbon steel
___________________ are all critical factors affecting sour water corrosion.
H2S content, pH, temperature, velocity and oxygen concentration
Sulfuric acid corrodes severely carbon steel ________ .
heat affected zones
Carbon steel corrosion rates increase significantly if the flow velocity exceeds about __________ or at acid concentrations below ____.
2 to 3 fps (0.6 to 0.9 m/s), 65%
Alloys such as __________ resist dilute acid corrosion and form a protective iron sulfate film on the surface.
Alloy 20, Alloy 904L and Alloy C-276
Corrosion of steel by dilute acid is usually in the form of __________ and becomes more severe with increasing temperature and velocity.
overall metal loss or pitting
_________ – a family of stainless steels that contain a mixed austenitic-ferritic structure
including Alloy 2205, 2304, and 2507
Duplex stainless steel
