Thermoplastic Scrubber
Jaroslav Prazan
Podlomní 4
636 00 Brno
Czech republic
Tel.: +420 548539654
Fax: +420 548539654
Contact: Prazan Jaroslav
Email:
Activities
The company is involved in the complex
design and engineering of all kinds of ther-
moplastic structures,
mainly tanks, septic
ones and vessels, both above and under the
ground. 15 years of practical experience in
this field have given us the extraordinary
position of being an expert in plastic vessels,
FEA analysis, computer design, production
technology and welding of all kinds of plas-
tic materials.
More then 800 of projects have been car-
ried out, not only in
Czech and Slovak
republic but also in Austria and Germany,
including expert appraisals of failures
Number of employees = 1.
Project description
An aboveground welded thermoplastic scrub-
ber had to be built in a draining piping system
for gas
waste products from a technological
process. The vessel is equipped by a nozzle sys-
tem for spraying liquid in the washing process
of waste gas.
Technical data
diameter 1800 mm
height 4350 mm
weight 750 kg
Program
ESA-Prima Win version 3.60
Modules
Linear static analysis of shells
Intersections
Stability of shells
Intelligent document
Analysis description
Plastics structures exhibit a viscoelastic behav-
iour, dependent on the time of load exposition,
the temperature and stress level reached in the
material. The analysis of the thermoplastic
starts with the long term strength and creep
modulus determination. The number of analy-
sis necessary is then related to these conditions.
In the case of this scrubber, 2 crucial states
were defined - the working state and the short
term loads states. Both states have the same
geometry and model of construction but differ
in the modulus of elasticity and in the allowable
stresses.
As a result 2 independent linear analy-
sis and 2 stability analysis were performed - a
working state of the construction
with the
creep modulus 270 Mpa and the impact of the
short term loads with the creep modulus 770
MPa. 2 documents -
working state and short
term loads, are enclosed.
Experience
The design of thermoplastic process equip-
ment, using the appropriate design parameters
and material properties can be completed with
a combination of hand calculations and com-
puter run Finite Element Analysis (FEA). FEA is
necessary to determine peak stresses at discon-
tinuities, corner joints, and to verify strain limits
etc.
For a complete FEA analysis,
which has to be
executed for thermoplastic process equipment,
a non-linear analysis should be accomplished.
However, this is usually impractical due to time,
lack of detailed material strength design data,
and the relatively low allowable design stresses
used.
Satisfactory designs have been consistently
accomplished by using a linear elastic FEA
approach and by using a constant on required
years of durability dependent creep modulus
value for the design allowable stresses.
Mea-
surements of fabricated thermoplastic struc-
tures indicate the linear elastic approach to be
a viable and relatively accurate prediction of
equipment stresses and deformations.
Conclusion
A complicated shape of thermoplastic vessels
requires powerful tools for simplifying the cre-
ation of the geometry - intersections are a
necessity.
Several linear solutions of the structure, varying
from creep modulus in relationship to the tem-
perature, time of load exposition and reached
stress level
must be analysed. Each of the linear
analysis must also be complemented by a sta-
bility check of the construction for the same
creep modulus value.
Sometimes the stability analysis does not give
the positive values of the critical factors,
depending on the geometry, loads and sup-
ports. Then the geometrical non-linear analysis
must be used to find out the remaining load
bearing capacity of the structure, several non-
linear analysis
with regularly increased loads
have to be performed till the collapse of the
solver gives the critical load factor value.
The number of equations solved normally
varies between 100.000 - 1,000.000. So the
requirements for a really fast solver are great,
mostly the iterative solver is used.
All
mentioned features are included in ESA-
Prima Win software, the best solution for FEA
of the thermoplastics vessels I have ever used.
66
Company
Project
Thermoplastic Scrubber
SCIA User Contest 2005 / Civil Engineering
2
Categorie
