Interference from TIG welders. How to filter?

Hello,

We have a range of welding machines, which have passed EMC testing here in the UK.
My problem is in China, where interference from TIG welders is causing our machines to misbehave.
To me there seems to be two possible causes. Interference on the incoming mains, or coming in via the welding cables.
We do have Y2 4n7, and 2.2uF caps across the welding earth, and mains earth.
Can anyone suggest more robust filtering that we could try to solve these problems?

Regards
Bob.

RF is more than likely the cause, but is difficult to reduce. It will require more shielding on sensitive electronics than normal. Even though something are compliant, does not necessarily mean it will remove all interference.

Before continuing, you will need to locate the exact cause.

A Faraday cage around the TIG welder location may work, but if it is portable then that will not work. But that is a very expensive proposition. Depends on serious the issue is.