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Standards for Rail Weld inspection vary widely, and it also depends what welding method is used – Flash-butt welding is normally checked using magnetic particle inspection (EN14587/ ISO17638) , and aluminothermic ‘welding’ is normally checked ultrasonically.
Broadly, I would suggest using the standards that correspond to other rail inspection work on the Network – Its a very long time since I had any involvement with Peru, and as I recall their main rail networks are fairly unusual, so the subway may be different.
Standards / procedures you may want to look at include:
Australia – ARTC Manual for NDT of Rail ETN-01-04
General EN14730 – Aluminothermic welding of new rails
UK RT/CE/S/055 Rail Testing, Ultrasonic procedures, (Procedure U6 is relevant)
You might also be interested in the approach we developed for London Underground – Contact me if you need more info.
https://www.thepwi.org/technical_hub_journal_technical_articles/pwi_journal_0119_vol137_pt1/pwi_journal_0119_vol137_pt1_implementation_weld_inspec_lu