Yes it is still possible to comply with ISO 3834 if you do not have an approved quality system so long as you can address the essential requirement of the standard. ISO 3834-1 Section 4 gives an outline.

Independent certification to ISO 3834 benefits manufacturers by providing an authoritative third party statement of commercial value. Certification can be achieved alongside an ISO 9001 certification or it can stand alone. The stand-alone option may be attractive to companies in which the welding operations are simple.

What happens if I want start using different grades of material which are not covered by my current certification?

Any change to the original certified scope will require recertification.

Does Part 2 of ISO 3834 cover Parts 3 or 4?

Yes, as Part 2 of ISO 3834 is the most stringent it will cover Parts 3 and 4. Likewise, Part 3 will cover Part 4.

What happens if I want to add another welding process to my certification?

You will need to apply to have the certification extended to cover the additional welding process; also the Responsible Welding Coordinator (RWC) will need to be interviewed to confirm that he has the necessary knowledge to coordinate the welding activities of the new process.