Specific alignment within \begin{align} environment

\documentclass{article}
\usepackage{amsmath}

\begin{document}



alignat:
\begin{alignat}{2}
   -0,1 &< E &&< 0,1 \\
    6,3 &< S &&< 6,4 \\
6,3-0,1 &<S+E&&< 6,4+0,1 \\
   -0,1 &< I &&< 6,5  
\end{alignat}
\end{document}

With array:

\documentclass{article}
\usepackage{amsmath,array}

\begin{document}

\begin{equation*}
\renewcommand{\arraystretch}{1.2} % like in cases
\setlength{\arraycolsep}{0pt} % use math spacings
\begin{array}{ r<{{}} c >{{}}l }
   -0{,}1   < &  E  & < 0{,}1 \\
    6{,}3   < &  S  & < 6{,}4 \\
6{,}3-0{,}1 < & S+E & < 6{,}4+0{,}1 \\
    6{,}2   < &  I  & < 6{,}5
\end{array}
\end{equation*}

\end{document}

align family environments, by nature, produce right/left alignments of successive columns. Thus they are not easily adapted to achieve the center-alignment of the middle column that was requested.

Also, in order to not treat the comma as punctuation, one can either enclose each comma in its own braces {,} (yuck!), or use the \cmac macro provided to use active commas to fix the problem...Just make sure you don't use commas in another context while \cmac is active.

With tabstackengine...

\documentclass{article}
\usepackage{tabstackengine}
\let\svcm,
{
\catcode`,=\active %
\gdef,{{\svcm}}
}
\newcommand\cmac{\catcode`,=\active }
\TABstackMath
\begin{document}
\[
  \TABbinary
  \cmac
  \setstacktabulargap{0pt}
  \tabularCenterstack{rcl}{
   -0,1 <& E &< 0,1 \\
    6,3 <& S &< 6,4 \\
6,3-0,1 <&S+E&< 6,4+0,1 \\
    6,2 <& I &< 6,5}
\]
\end{document}

If one wants more vertical spacing between the lines, simply add \setstackgap{L}{1.2\baselineskip} to the mix: