Equation Numbering by Parts

Im wondering how I can number equations by parts and sections? For instance, for part 1 section 2 I want the equation numbering to be (1.2.1), (1.2.2) etc. My document class is elsarticle. I know that I can use numberwithin{equation}{section} to get numbering according to sections but this does not work for parts.

Below is how I have set up my document:

documentclass[3p]{elsarticle}



makeatletter

defps@pprintTitle{
   let@oddhead@empty
   let@evenhead@empty
   def@oddfoot{reset@fonthfilthepagehfil}
   let@evenfoot@oddfoot
}

hypersetup{        
    colorlinks=true,
    linkcolor=blue,
    filecolor=magenta,      
    urlcolor=cyan,
}

renewenvironment{abstract}{globalsetboxabsbox=vboxbgroup
hsize=textwidthdefbaselinestretch{1}%
noindentunskiptextbf{Abstract}
parmedskipnoindentunskipignorespaces}
{egroup}

setcounter{totalnumber}{5}
renewcommand{textfraction}{0.05}
renewcommand{topfraction}{0.95}
renewcommand{bottomfraction}{0.95}
renewcommand{floatpagefraction}{0.35}

bibliographystyle{ieeetr}
setlength{bibsep}{0.5baselineskip}%


numberwithin{equation}{section}

begin{document}

...


end{document}