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CORROSION

                                                                                           “You can use

                                                                                           COMSOL Multiphysics
                                                                                           with the Corrosion
                                                                                           Module to solve this
                                                                                           problem. All the work
                                                                                           that previously seemed
                                                                                           so difficult, now is so
                                                                                           easy because you have
                                                                                           the module doing a lot
                                                                                           of the work for you”

                                                                                           –SIDDIQ QIDWAI, MECHANICAL

                                                                                            ENGINEER, NRL

                                                                                           The properties of 316 steel were custom-

                                                                                           defined in the model. Simulation results

FIGURE 2. Corrosion in metals, such as stainless steel, is the result of electrochemical   in the COMSOL environment, presented
reactions and mass transport in an electrolyte solution. An irregular corrosion front      in Figure 4, demonstrate localized loss of
develops due to the material microstructure.                                               material due to pitting.
                                                                                           	 In developing their multiphysics model

                                                                                           of pitting corrosion, Qidwai found that

	                                            the crystal orientation to calculate the      “COMSOL is so versatile that it will give
	 “In developing a complex model, our        corresponding pitting potential, which in     you a solution even for very complex
strategy is to start with simpler numerical  turn determines the corrosion rate and        applications. This is where experimental
studies. Currently in our simulations        movement of the front,” says Qidwai.          validation is the key.” Insight gained from
we solve the electrochemical and mass        The pitting potential is determined in        their simulations has already provided
transport equations separately. In future    MATLAB® for a particular crystallographic     the impetus for the development of a
work, we will create a fully-coupled         orientation and ultimately used by the        novel experimental method to evaluate
electrochemical mass transport model of      COMSOL model to calculate the corrosion       corrosion at the micron scale. The results
corrosion.” To create their models, they     rate and advance the corrosion front.         from the experiments will be used to
have used the transport of diluted species   “LiveLink™ for MATLAB® has been an            validate the model and establish the
physics for mass transport, the Laplace      essential feature for us in order to include  relationship between microstructure, pit
and Poisson’s equations for the electric                                                   shape, and growth.

potential, and the moving mesh (ALE)         the effect of the metal microstructure.”

technology for the corrosion front. “You

can use COMSOL Multiphysics with the

Corrosion Module to solve this problem,”

says Qidwai. “All the work that previously

seemed so difficult, now is so easy because

you have the module doing a lot of the

work for you.”

	 Incorporating the microstructure into

a multiphysics model of pitting corrosion

is a formidable challenge tackled initially

at NRL through the use of orientation

imaging microscopy (OIM) to acquire 3D

images of the metal microstructure. An

OIM-based reconstructed image of steel is

shown in Figure 3.

	 An integrated method was used to

incorporate the microstructure of 316

steel into a multiphysics model of pitting   FIGURE 3. At right, the model geometry implemented in COMSOL Multiphysics to
corrosion implemented in the COMSOL®         evaluate pit growth in metals. The reconstructed metal microstructure, at left, was
environment. “At every location along the    determined using orientation imaging microscopy at NRL. The colored legend corresponds
corrosion front, 
we have to determine       to the crystallographic orientation of each grain.

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