Custom line style with custom decoration

Question

I want to create a flanged version of 3D pipes that look like the picture in the original post. My "brute force" attempt goes as follows:

\documentclass[tikz]{standalone}

\begin{document}

\begin{tikzpicture} 
\definecolor{LPtgrey}{rgb}{.7,.7,.7}
\def\pipesize{1cm}
\def\flangesize{1.75*\pipesize}
\def\ft{0.2} % for flange thickness
\def\fg{0.02} % for flange gap
\def\xx{0.5} % length of middle of bend to inside edge of flange, ie, same as bend radius
\pgfsetcornersarced{\pgfpoint{0.5cm}{0.5cm}}
%pipe
\draw[color=LPtgrey!80!black, line width=\pipesize*0.4] (2,0)--(2,6)--(5,6)--(7,4)--(9,4);%
\draw[color=LPtgrey, line width=\pipesize*0.38] (2,0)--(2,6)--(5,6)--(7,4)--(9,4);%
\draw[color=LPtgrey!85, line width=\pipesize*0.35] (2,0)--(2,6)--(5,6)--(7,4)--(9,4);%
\draw[color=LPtgrey!70, line width=\pipesize*0.32] (2,0)--(2,6)--(5,6)--(7,4)--(9,4);%
\draw[color=LPtgrey!55, line width=\pipesize*0.29] (2,0)--(2,6)--(5,6)--(7,4)--(9,4);%
\draw[color=LPtgrey!45, line width=\pipesize*0.25] (2,0)--(2,6)--(5,6)--(7,4)--(9,4);%
\draw[color=LPtgrey!35, line width=\pipesize*0.20] (2,0)--(2,6)--(5,6)--(7,4)--(9,4);%
%flange 1
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (2,0)--(2,0+\ft);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (2,0)--(2,0+\ft);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (2,0)--(2,0+\ft);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (2,0)--(2,0+\ft);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (2,0)--(2,0+\ft);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (2,0)--(2,0+\ft);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (2,0)--(2,0+\ft);%
%flange 2
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (2,6-\xx-\ft-\fg-\ft)--(2,6-\xx-\ft-\fg);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (2,6-\xx-\ft-\fg-\ft)--(2,6-\xx-\ft-\fg);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (2,6-\xx-\ft-\fg-\ft)--(2,6-\xx-\ft-\fg);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (2,6-\xx-\ft-\fg-\ft)--(2,6-\xx-\ft-\fg);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (2,6-\xx-\ft-\fg-\ft)--(2,6-\xx-\ft-\fg);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (2,6-\xx-\ft-\fg-\ft)--(2,6-\xx-\ft-\fg);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (2,6-\xx-\ft-\fg-\ft)--(2,6-\xx-\ft-\fg);%
%flange 3
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (2,6-\xx-\ft)--(2,6-\xx);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (2,6-\xx-\ft)--(2,6-\xx);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (2,6-\xx-\ft)--(2,6-\xx);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (2,6-\xx-\ft)--(2,6-\xx);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (2,6-\xx-\ft)--(2,6-\xx);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (2,6-\xx-\ft)--(2,6-\xx);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (2,6-\xx-\ft)--(2,6-\xx);%
%flange 4
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (2+\xx,6)--(2+\xx+\ft,6);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (2+\xx,6)--(2+\xx+\ft,6);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (2+\xx,6)--(2+\xx+\ft,6);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (2+\xx,6)--(2+\xx+\ft,6);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (2+\xx,6)--(2+\xx+\ft,6);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (2+\xx,6)--(2+\xx+\ft,6);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (2+\xx,6)--(2+\xx+\ft,6);%
%flange 5
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (2+\xx+\ft+\fg,6)--(2+\xx+\ft+\fg+\ft,6);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (2+\xx+\ft+\fg,6)--(2+\xx+\ft+\fg+\ft,6);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (2+\xx+\ft+\fg,6)--(2+\xx+\ft+\fg+\ft,6);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (2+\xx+\ft+\fg,6)--(2+\xx+\ft+\fg+\ft,6);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (2+\xx+\ft+\fg,6)--(2+\xx+\ft+\fg+\ft,6);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (2+\xx+\ft+\fg,6)--(2+\xx+\ft+\fg+\ft,6);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (2+\xx+\ft+\fg,6)--(2+\xx+\ft+\fg+\ft,6);%
%flange 6
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (5-\xx-\ft-\fg-\ft,6)--(5-\xx-\ft-\fg,6);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (5-\xx-\ft-\fg-\ft,6)--(5-\xx-\ft-\fg,6);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (5-\xx-\ft-\fg-\ft,6)--(5-\xx-\ft-\fg,6);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (5-\xx-\ft-\fg-\ft,6)--(5-\xx-\ft-\fg,6);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (5-\xx-\ft-\fg-\ft,6)--(5-\xx-\ft-\fg,6);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (5-\xx-\ft-\fg-\ft,6)--(5-\xx-\ft-\fg,6);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (5-\xx-\ft-\fg-\ft,6)--(5-\xx-\ft-\fg,6);%
%flange 7
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (5-\xx-\ft,6)--(5-\xx,6);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (5-\xx-\ft,6)--(5-\xx,6);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (5-\xx-\ft,6)--(5-\xx,6);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (5-\xx-\ft,6)--(5-\xx,6);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (5-\xx-\ft,6)--(5-\xx,6);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (5-\xx-\ft,6)--(5-\xx,6);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (5-\xx-\ft,6)--(5-\xx,6);%
%flange 8
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (5+\xx,6-\xx)--(5+\xx+\ft,6-\xx-\ft);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (5+\xx,6-\xx)--(5+\xx+\ft,6-\xx-\ft);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (5+\xx,6-\xx)--(5+\xx+\ft,6-\xx-\ft);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (5+\xx,6-\xx)--(5+\xx+\ft,6-\xx-\ft);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (5+\xx,6-\xx)--(5+\xx+\ft,6-\xx-\ft);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (5+\xx,6-\xx)--(5+\xx+\ft,6-\xx-\ft);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (5+\xx,6-\xx)--(5+\xx+\ft,6-\xx-\ft);%
%flange 9
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (5+\xx+\ft+\fg,6-\xx-\ft-\fg)--(5+\xx+\ft+\fg+\ft,6-\xx-\ft-\fg-\ft);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (5+\xx+\ft+\fg,6-\xx-\ft-\fg)--(5+\xx+\ft+\fg+\ft,6-\xx-\ft-\fg-\ft);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (5+\xx+\ft+\fg,6-\xx-\ft-\fg)--(5+\xx+\ft+\fg+\ft,6-\xx-\ft-\fg-\ft);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (5+\xx+\ft+\fg,6-\xx-\ft-\fg)--(5+\xx+\ft+\fg+\ft,6-\xx-\ft-\fg-\ft);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (5+\xx+\ft+\fg,6-\xx-\ft-\fg)--(5+\xx+\ft+\fg+\ft,6-\xx-\ft-\fg-\ft);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (5+\xx+\ft+\fg,6-\xx-\ft-\fg)--(5+\xx+\ft+\fg+\ft,6-\xx-\ft-\fg-\ft);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (5+\xx+\ft+\fg,6-\xx-\ft-\fg)--(5+\xx+\ft+\fg+\ft,6-\xx-\ft-\fg-\ft);%
%flange 10
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (7-\xx-\ft-\fg-\ft,4+\xx+\ft+\fg+\ft)--(7-\xx-\ft-\fg,4+\xx+\ft+\fg);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (7-\xx-\ft-\fg-\ft,4+\xx+\ft+\fg+\ft)--(7-\xx-\ft-\fg,4+\xx+\ft+\fg);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (7-\xx-\ft-\fg-\ft,4+\xx+\ft+\fg+\ft)--(7-\xx-\ft-\fg,4+\xx+\ft+\fg);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (7-\xx-\ft-\fg-\ft,4+\xx+\ft+\fg+\ft)--(7-\xx-\ft-\fg,4+\xx+\ft+\fg);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (7-\xx-\ft-\fg-\ft,4+\xx+\ft+\fg+\ft)--(7-\xx-\ft-\fg,4+\xx+\ft+\fg);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (7-\xx-\ft-\fg-\ft,4+\xx+\ft+\fg+\ft)--(7-\xx-\ft-\fg,4+\xx+\ft+\fg);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (7-\xx-\ft-\fg-\ft,4+\xx+\ft+\fg+\ft)--(7-\xx-\ft-\fg,4+\xx+\ft+\fg);%
%flange 11
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (7-\xx-\ft,4+\xx+\ft)--(7-\xx,4+\xx);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (7-\xx-\ft,4+\xx+\ft)--(7-\xx,4+\xx);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (7-\xx-\ft,4+\xx+\ft)--(7-\xx,4+\xx);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (7-\xx-\ft,4+\xx+\ft)--(7-\xx,4+\xx);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (7-\xx-\ft,4+\xx+\ft)--(7-\xx,4+\xx);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (7-\xx-\ft,4+\xx+\ft)--(7-\xx,4+\xx);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (7-\xx-\ft,4+\xx+\ft)--(7-\xx,4+\xx);%
%flange 12
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (7+\xx,4)--(7+\xx+\ft,4);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (7+\xx,4)--(7+\xx+\ft,4);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (7+\xx,4)--(7+\xx+\ft,4);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (7+\xx,4)--(7+\xx+\ft,4);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (7+\xx,4)--(7+\xx+\ft,4);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (7+\xx,4)--(7+\xx+\ft,4);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (7+\xx,4)--(7+\xx+\ft,4);%
%flange 13
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (7+\xx+\ft+\fg,4)--(7+\xx+\ft+\fg+\ft,4);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (7+\xx+\ft+\fg,4)--(7+\xx+\ft+\fg+\ft,4);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (7+\xx+\ft+\fg,4)--(7+\xx+\ft+\fg+\ft,4);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (7+\xx+\ft+\fg,4)--(7+\xx+\ft+\fg+\ft,4);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (7+\xx+\ft+\fg,4)--(7+\xx+\ft+\fg+\ft,4);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (7+\xx+\ft+\fg,4)--(7+\xx+\ft+\fg+\ft,4);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (7+\xx+\ft+\fg,4)--(7+\xx+\ft+\fg+\ft,4);%
%flange 14
\draw[color=LPtgrey!80!black, line width=\flangesize*0.4] (9-\ft,4)--(9,4);%
\draw[color=LPtgrey, line width=\flangesize*0.38] (9-\ft,4)--(9,4);%
\draw[color=LPtgrey!85, line width=\flangesize*0.35] (9-\ft,4)--(9,4);%
\draw[color=LPtgrey!70, line width=\flangesize*0.32] (9-\ft,4)--(9,4);%
\draw[color=LPtgrey!55, line width=\flangesize*0.29] (9-\ft,4)--(9,4);%
\draw[color=LPtgrey!45, line width=\flangesize*0.25] (9-\ft,4)--(9,4);%
\draw[color=LPtgrey!35, line width=\flangesize*0.20] (9-\ft,4)--(9,4);%
\end{tikzpicture}
\end{document}

the result is ok-ish:

Brute force works OK for 90 degree turns, but 45 degree angles have flanges that are too thick. Other angles require too much trigonometry to calculate the flange positions.

1. There must be a way to define a "line style" which is the combination of 5 overlapping lines (I don't know how).

2. There must be a way to define a custom decoration that would terminate each line (or each node of a polyline) to get the result desired. Would the decoration rotate to be at the same angle as the line?

Ideally, I'd like to use code like:

\draw[pipe,style=flange,diameter=3cm](2,0)--(2,6)--(5,6);

and all the math associated with flange placements would be taken care of. I will be drawing LOTS of pipe diagrams in the near future and would appreciate any helpful code that would make it easier.

Answer 1

Two approaches are demonstrated here. Both repeatedly use the preaction key with different line widths and colors to draw the pipe (and also the flange). The first approach uses the markings decoration as a postaction to position the flanges. The second uses the show path construction decoration to position flanges at the beginning and ends of lineto and curveto segments.

\documentclass[tikz,border=5]{standalone}
\usetikzlibrary{decorations.markings,decorations.pathreplacing,calc}
\makeatletter
\tikzset{every pipe/.code={%
  \pgfmathloop
  \ifnum\pgfmathcounter>20
  \else
    \pgfmathsetmacro\i{\pgfmathcounter}%
    \pgfmathsetmacro\j{80-\pgfmathcounter*3}%
    \tikzset{preaction/.expanded={line width=(\pipewidth)*(1-\i*\i/500),
        draw=black!50!white!\j!white}}%
  \repeatpgfmathloop
},
every flange/.style 2 args={insert path={
  let \p1=(#1), \p2=(#2),\n1={atan2(\y2-\y1, \x2-\x1)} in
    [shift={(\p1)}, rotate=\n1, pipe width={(\pipewidth)*4/3}, every pipe] 
      (0.01,0) -- (0.2,0)
}},
flanges/.style={postaction={%
  /utils/exec={
    \@for\pos:=#1\do{%
      \tikzset{decoration/.expanded={markings,
        mark=at position \pos\space with {
          \noexpand\path [pipe width=\pipewidth*4/3, every pipe] (0.01,0) -- (0.2,0);
    }}}}}, 
  decorate}},
pipe width/.code=\pgfmathsetlengthmacro\pipewidth{#1},
pipes/.style={
  every pipe,
  postaction={decoration={show path construction,
    lineto code={
      \path [every flange={\tikzinputsegmentfirst}{\tikzinputsegmentlast}];
      \path [every flange={\tikzinputsegmentlast}{\tikzinputsegmentfirst}];
    },
    curveto code={
      \path [every flange={\tikzinputsegmentfirst}{\tikzinputsegmentsupporta}];
      \path [every flange={\tikzinputsegmentlast}{\tikzinputsegmentsupportb}];
    }
}, decorate}},
pipe/.style={
  every pipe,
  flanges={0, 1}
}}
\begin{document}
\begin{tikzpicture}[line join=round, pipe width=0.5cm]
\path [pipes] (0,4) -- (0,1) arc (180:330:1) (-1,3) -- (1,3);
\path [pipes] (3,-1/3) -- (3,2);
\path [pipes] (4,-1/3) -- (4,4);
\path [pipe]  (11/2,3) -- (4,5/4) -- (11/2,0);
\path [pipe]  (13/2,5/2) -- (8,5/2) -- (13/2,0) -- (8,0);
\path [pipes] (4,2) ellipse [x radius=6, y radius=4];
\end{tikzpicture}
\end{document}