Safety survey for critical Equipments like pressure vessels, Converters,
Absorption towers, furnaces, silos, etc. are usually done using experience, and certain
basic data like Ultrasonographic tests on the shell plate. All these data / methods show
the thickness at different regions of the shell plate only. They donot give an insight
into the actual condition of the equipment. In order to know the kind of stress developed
in the shell plates, a stress analysis using the finite element method will be required.
This method, being highly time taking was usually was usually avoided in the past.
However, with the advent of the computer, and particularly the highly reliable softwares,
the detailed deformation, and stress distribution for the entire equipment under operating
loads is available in hard copies of coloured displays known as stress contours. These
softwares require the inputs of the entire 3-Dimensional geometry of the equipment, like
shell thickness, details of openings, etc, along with all loads like temperature,
pressure, liveloads, etc. After a stress analysis with the given loads has been performed,
the software would depict the effect the effect of these loads on the structure, including
the deflected shape, showing the deflection at each region, and the stress contour which
shows the stress at each and every point. This stress contour, and the deformation diagram
in 3-Dimensions will aid in visualisation of the stress conditions, and the deformation
geometry in totality for the entire equipment.
degree of corrosion under chemically reactive atmosphere is directly proportional to the
stress intensity. The corrosion will be more pronounced at the high stressed zones of the
structure. In thermal conditions, (other than cryogenic conditions) rise in temperature
induces higher stress that accelerates corrosion. Once the highly stressed conditions in
an equipment are determined through a finite element analysis, it is obvious that this
would be the region subjected to the worst corrosion in future, and result in further over
stressing. The maintenance and safety departments of the plant could then take adequate
measures to relieve these regions of the stress, so that all the regions are equally
stressed, thereby avoiding heavy corrosion to any one particular area.
with this data the residual life of the equipment, and the time for repair could be
accurately determined. This technology could be applied to the long time planning of
safety requirements & preventive maintenance, primarily to counteract the aggressive
chemical corrosion, thermal stresses, fatigue conditions due to dynamic loads, etc,
assuring a longer service life for the equipment.
would eliminate crisis management of maintenance, arising out of non-availability of data
to predict distress. The maintenance department would not need to repair an equipment
after the damage is already done, but instead, each equipment would be subjected to
preventive maintenance at predetermined areas as predicted by the stress contours, much
before the equipment could fail / leak and create disruption of production.