Does anyone know how to design a spiraled steam tracing for a pipe (number of spirals, spacing between spirals, tracing diameter)?
I can't find any good reference on the subject...

You cannot use a spiral configuration for steam tracing. The tracing must be arranged such that the condensate can gravity drain to a low point with a trap.and you will obtain all the information and help you need on this subject.  Note that in order to be an effective application, you should employ a cement that physically binds the straight, steam tubing to the metal pipe.  This cement serves the purpose of supplying the solid medium through which the heat conduction is transferred.

Supplemental remark: Electric heating cable/tape is frequently spiraled on to piping, but also frequently mis-installed when it gets to a pump or valve. You can't wrap a component with a big snarl of heat tape: if the tape crosses itself you'll get hot spots and probably abbreviated service life.

The above comments are correct, however they are also incomplete, you should also know that:

1)   Steam tracing(Bellow Seal Valves) must always follow the bottom of piping, not spiral like electric tracing. The tracing is typically encapsulated in a "half moon" cover with a heat conducting adhesive

2)   Where large valves or similar in-line components must be traced, you must loop the tube to allow drainage

3)   There are length maxima. drainage slope, trap capacities and other factors that affect your steam trap "circuit" length

Finally, the people who have "written the book" on steam tracing are the kind and helpful people at Spirax Sarco...

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