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
