I think a lot of it will come down to the scale of the model. String and tape would not look out of place on a small workshop engine or on a small launch which would typically be plumbed up with screw fittings say upto 2" BSP.
Once you start getting upto larger engines found in a factory, pumping station ot large ship which would more likely have the pipework and fittings joined with flanged connections the string/tape looks out of place and heh smoother insulation more in keeping.
Just had a look at James Lauders medal winning Leake compound and he used a similar method to the one in my previously posted link
Edited By JasonB on 21/07/2016 13:25:21