The first thing to do, is to create the shape of a pipesystem. I recommend that you do this in CorelDraw but it could also be done in Photoshop by using the path-tool.

Select the shape with the magic wand tool and add a new layer. Fill the selection with a light yellow shade.

While the selction still on, Go to FILTERS/BLUR and select GUSSIAN BLUR with Radius 5. Do this twice.

Now, go to FILTER/RENDER and Lightning effects.
Apply the approx. settings as shown here above

Apply the Layer effect Innershadow with the direction from bottom right.
Use a light shade of any color. I used orange.
....and this is the result.