Simulation of Crack Propagation in a Centrifugal Pump Casing

www.clydepumps.com1© CLYDEUNION Pumps 2011

Simulation of crack propagation in a centrifugal pump casing

Ramana .Podugu

Dy Manager-FEA

CUEC

Bangalore


Engineering Problem

• Detecting the reason for the crack initiation at the cutwater region of a centrifugal pump casings using Ansys.

• Simulating the crack propagation along the volute of the casing from the cutwater region using Ansys and Franc3D soft wares.

• Finding good understanding between test results and FEA results.


Meshing Model

Boundary conditions

Hydro static pressure 12.4Mpa (1800 psi) is

applied normal to the wetted surface.

Static stress analysis

Boundary conditionsBoundary conditions

Loading conditions Material data:


Stress distribution at the cutwater region


Work flow between ansys and Franc 3D

Global Model

Local Model Sub modeling approach

• The area where crack has initiated is separated from

the main model and considered as local model

•The main model is considered as global model .

• The both parts are written into CDB files with the

boundary and pressure conditions.

• Used sub modelling approach to save the runtime

and computation time.


Crack insertion procedure in Franc3D

Crack type

Crack sizeCrack size

Crack orientation

Crack front radius

Mesh refinement at the cutwater region in franc3D


Connection between franc3D and Ansys


Stress intensity factor

The Initial stress concentration at the crack insertion is 95 Ksi inch^0.5

Finding SIF using J-Integral

AB


Displacement field at the crack

Maximum displacement at the initial crack is 0.03895 inch


Maximum Von-misses stress at the initial crack is 798030 Psi

Plastic zone ahead of the crack tip

Stress field at the crack


Crack Propagation techniques

Once the SIF solution for a given crack front is obtained, FRANC3D provides tools to estimate a new, propagated crack front. Because KI is in generally not constant along the crack front, the crack will not propagate evenly across the font . The user specifies the maximum propagation increment anywhere along the crack, delta amax, which would of course corresponding to the point where KI is highest. The crack extension everywhere else on the crack front is calculated based on the Paris power law.


Crack front at the 73 load step

Crack Propagation at the critical area


Crack propagation at the 74 load step.

Crack Propagation at the critical area


Crack propagation along the cut water region- Inner side of the casing

Crack propagation at the last step


Crack propagation along the cut water region- outer side of the casing

Crack propagation at the last step


Results

SIF plot along the crack lenght

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

0.000 2.000 4.000 6.000 8.000 10.000 12.000 14.000

Crack lenght ,inch

SIF

,Ksi

ro

ot

squ

are

(in

ch) Original design


Crack formed at the cutwater region (inside the casing)

Results validation

FEA results Test results


Crack formed at the cutwater region (outside the casing)

Results validation

FEA results Test results

Simulation of Crack Propagation in a Centrifugal Pump Casing

Documents

Transcript of Simulation of Crack Propagation in a Centrifugal Pump Casing