fuel gas pipes flushing

[pekos]

We have troubles with our furnaces fuel gas system, frequent clogging problems in burners and their feeding piping branches..so we are considering a flushing of the pipes
we used to do it with steam (3-4 bar), but got no results.
is there any means to use a more efficient solution to flush these pipes?

 

[TD2K]

What's causing the plugging?

 

[pekos]

TD2K
I did some analysis on deposits sample:
Iron: 24.4%
Manganese: 0.14%
lead: 0.15%
zn: .04%
antimony: 0.07%
Cu: 0.02%

loss at 550°c: 22%