I believe you have a good reference (as a company procedure) from Mr. Lee.
In addition, the followings should be confirmed by your client for the project.
- the number/percent of test
- the locations of the test
- the applicable standards (e.g., A380, para 7.3.4/ or A967, para.19) or procedure
- the acceptance categories if your client have. If not, see A380, para 7.3.4 for reference.
FERROXYLTESTFORIRONCONTAMINATION.pdf