03-05-2014, 12:02 PM
Analysis and Estimation of Attenuation Coefficient of Aging EN-19 Steel
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ABSTRACT
The mechanical properties of in-service
facilities are required to evaluate the strength of
process equipments. The purpose of this paper is
to analyze the relationship between the
mechanical properties and the attenuation
coefficient of ultrasonic testing. For experimental
tests we have selected EN-19 steel as reference.
EN-19 steel is subjected to four different
isothermal aging at a temperature of 700 0C and
an original specimen respectively. For these
specimens tensile tests, hardness test, impact tests
and ultrasonic tests were performed. Attenuation
coefficients of ultrasonic testing were determined
using Pulse-Echo ultrasonic test. A good analysis
and estimation between mechanical properties
and attenuation coefficient was found
INTRODUCTION
For the reliable estimation of remaining life
of in-service process equipments, the degradation of
material properties of these equipments must be
analyzed. These equipments undergo degradation due
to prolonged exposure to high temperature. The
degradation of mechanical properties affects the
safety of operating facilities. Isothermal aging of
material varies the EN-19 steel, which is mainly used
in various elements like gears, axels, drive shafts,
induction hardening pins and high strength shafts.
ULTRASONIC TESTING
Ultrasonic testing (UT) is a non-destructive
inspection method that uses high frequency sound
waves (ultrasound) that are above the range of human
hearing, to measure geometric and physical
properties in materials. Ultrasound travels in different
materials at different speeds (velocity). However, the
speed of sound propagation in a given material is a
constant
ULTRASONIC ATTENUATION
Measurement of ultrasonic attenuation in cast steel
components will provide useful information in the
assessment of the grain size and thereby on the effect
of heat treatment. The grain size of as-cast steel is
large and high attenuation is caused by the ultrasonic
beam being scattered by the large grains. In the fully
heat treated condition, when the temperature of the
heat treatment exceeds the transformation
temperature, the as-cast grain structure is
recrystallized.
PULSE ECHO TEST METHOD
A pulse echo configuration was used in this work
with transducer and all signals were taken at normal
incidence on the interface of specimen. In this
inspection mode, a single transmitter-receiver
transducer scans along the material surface capturing
signals that have been reflected from the back
surface, or from discontinuities (interfaces or defects)
in the material. Additional echoes are produced due
to the presence of discontinuities within the region
being interrogated. In the presence of a defect, the
incident pulse is almost totally reflected at the
interface with little or no ultrasonic signal transmitted
to the material below the defect.
CONCLUSION
To investigate the mechanical properties
using ultrasonic technique, we prepared for five
different simulated specimens of EN 19 STEEL by
isothermal aging heat treatment. By comparing
various mechanical properties obtained from tensile
and impact test with ultrasonic parameters of these
specimens such as attenuation, the following
conclusions were obtained.