How often do I need to test?

Regularly! Having used SIR to achieve OE, you now need to prove it repeatably! You can do this quickly and effectively on a shop floor using the Ionic Contamination technique for process control.
If OE study has been completed then the PICT test is used to establish that OE is being met on a routine basis. If a process or materials are changed this can trigger a new OE evaluation using the SIR test, and from this a new PICT value can be established and the process limits are updated.

The implementation of many standards are monitored by independent auditors. The user supplier relationship may arrange for auditing to be carried on a regular basis. The timing of these audits should consider the stability of the process and the need to refresh the original establishment of OE and SIR test results. Initially a more cautious approach may be adopted until the stability pf the process is understood.