I create a single column table using tabu.
\documentclass[preprint,5p,12pt]{elsarticle}
\usepackage{tabu}
\begin{document}
\begin{table}[htbp]
\footnotesize
\begin{center}
\label{T:my_table}
\everyrow{\hline}
\tabulinesep=1.2mm
\begin{tabu} to \linewidth {|X{l}|}
\textbf{Headline 1} \\
a \\
b \\
c \\
\hline \hline
\textbf{Headline 2} \\
d \\
e \\
f \\
g \\
\end{tabu}
\caption{Meaningful caption}
\end{center}
\end{table}
\end{document}
This renders without a line on the right. How can i get a right border for all rows?