Automatically select nodes

Hello all, 

I'm writing a code to automatically select some nodes close to welding points to put them into a set to further post process it. 

I wrote most part of the code to select automatically a few types of welds, but I'm having problem to select the nodes for the weld representation below. 

The script just ask for the weld components and automatically select the nodes. The nodes showed on the figure have an specified distance from the weld toe but I still don't know how to use this distance to select what I want. 

Any ideas on how to achieve it? 

I can provide some piece of the codes if need. 

<?xml version="1.0" encoding="UTF-8"?>