NOM-020-STPS Audit Preparation for Inspection Companies
A NOM-020-STPS audit runs in 7 stages, beginning with classify each item into category i, ii or iii per clause 7.. Secretaría del Trabajo y Previsión Social (STPS); conformity assessed by unidades de inspección (statutory term until 2020: unidades de verificación) that are accredited by an accreditation entity and approved by STPS tests the system by sampling finished work backwards to the records behind it, so preparation means.
The current designation is confirmed: NOM-020-STPS-2011, published in the Diario Oficial de la Federación on 27 December 2011 and in force from 27 June 2012, superseding NOM-020-STPS-2002, with an authorised alternative procedure published 9 December 2014 and continued validity confirmed by systematic review on 15 August 2022. It is the engine of the Mexican NDT inspection market because it makes periodic non-destructive examination or pressure testing mandatory rather than discretionary for Category II and III equipment. The employer classifies each item into Category I, II or III from fluid hazard, relief-device set pressure and volume, maintains a per-equipment file, and either contracts an accredited inspection unit or — for Category III only — constitutes its own Type B unit. What separates firms that clear an audit from firms that collect findings is not the quality of the documentation but whether it describes what actually happens.
Source: NOM-020-STPS-2011 as published in the Diario Oficial de la Federación, Segunda Sección, Tuesday 27 December 2011, retrieved from the STPS document repository at asinom.stps.gob.mx and extracted; clauses 3.7, 4.19 to 4.21, 4.32, 4.41 to 4.43, 7 and Table 1, 13.1 to 13.6, 16, 17, 19 and 20, and Reference Guide III read directly. Status as vigente, entry into force on 27 June 2012, the authorised alternative procedure of 9 December 2014, and the systematic review confirmation of 15 August 2022 from the Sistema Nacional de Infraestructura de la Calidad catalogue at platiica.economia.gob.mx. NMX-B-482-CANACERO-2016 — full title, vigente status, DOF declaratoria de vigencia of 20 October 2016, CANACERO as issuing Organismo Nacional de Normalización, cancellation of NMX-B-482-1991, and its recorded international grade of 'no equivalente' — from the same catalogue. Limitation: the text of NMX-B-482-CANACERO-2016 itself was not obtained, so its internal qualification model is not characterised here beyond its recorded grade. Verified 21 August 2026.
| Stage | What happens | What it tests |
|---|---|---|
| Stage 1 | Classify each item into Category I, II or III per clause 7 and Table 1, using the set pressure of. | Where the paperwork is tested against itself |
| Stage 2 | Build and maintain the per-equipment file, operating and maintenance procedures, and train the workers involved. | Where the paperwork is tested against practice |
| Stage 3 | Perform the pressure test or NDT on the statutory cycle — for new Category II and III equipment holding a. | Where the paperwork is tested against practice |
| Stage 4 | Select the NDT scope — clause 13. | Where the paperwork is tested against practice |
| Stage 5 | For Category III equipment, perform the test or examination in the presence of a Type A, B or C unidad. | Where the paperwork is tested against practice |
| Stage 6 | The unidad de inspección issues the dictamen de evaluación de la conformidad, carrying its accreditation number, the dates of accreditation. | Where the paperwork is tested against practice |
| Stage 7 | For Category III, file the aviso with STPS within sixty days of the dictamen; STPS assigns a número de control. | Where the paperwork is tested against practice |
| Renewal | For Category II and III equipment: the first pressure test or NDT is due before ten years from the manufacturing certificate or code stamp for new equipment that has one; equipment without that certificate or stamp, and all used equipment, is tested before entering service. Thereafter at least every five years, performed within the sixty calendar days before the end of each five-year period. The periodicity is determined by the employer's qualified personnel and may in no case exceed five years (clause 13.2 a). Dictámenes issued by a unidad de inspección are valid ten years for new equipment and five years for used equipment (clause 19.7). Boilers additionally require functional testing of safety shutdowns. Category III equipment requires a notice to STPS within sixty days of the dictamen. | Diarised from the certificate date, not the last audit |
How long does NOM-020-STPS audit preparation take?
Document work — the written practice, procedures and quality manual — takes weeks. What cannot be compressed is documented experience and records history: on-the-job hours accrue in real time, and calibration and certification history cannot be back-filled. Firms that start when the audit is scheduled rather than announced clear it without findings.
What does Secretaría del Trabajo y Previsión Social (STPS); conformity assessed by unidades de inspección (statutory term until 2020: unidades de verificación) that are accredited by an accreditation entity and approved by STPS look at first?
Records, not manuals. A manual states intent; records show practice. The usual opening move is to take a completed job and trace it back to the technician's certification, the instrument's calibration, the approved procedure and the report — and see whether all four reconcile.
What are the most common NOM-020-STPS findings?
Equipment misclassified into Category I or II to escape the Category III duties to have a unidad de inspección present and to notify STPS, Only a volumetric examination performed, with no accompanying surface or flux-loss examination as clause 13.5 requires, NDT results endorsed by a technician whose certification cannot be traced to NMX-B-482, its replacement, or a demonstrably equivalent scheme, Pressure test endorsed by an NDT technician rather than by an engineer with knowledge in the matter, contrary to clause 13.2 f and i. Almost all of them are evidence problems rather than capability problems: the work was done correctly and the proof was not kept, or was kept somewhere the firm could not retrieve during the audit.
Can a consultant attend the NOM-020-STPS audit?
Yes, and it changes the outcome. Someone who has sat through the same audit at other firms answers in the auditor's own terms, produces the right record without a search, and stops a clarification turning into a finding. The firm still owns every answer — the consultant does not speak for it.
What happens after a NOM-020-STPS finding?
A corrective action with a deadline, and evidence of closure at the next audit. Repeat findings are treated far more seriously than first ones, because they show the corrective-action system itself is not working.
Does NOM-020-STPS require a pre-audit or gap assessment?
Not as a requirement, but the arithmetic favours it: a gap assessment finds the same evidence problems the auditor would, without the finding attached, and while there is still time to fix them. Firms entering their first NOM-020-STPS audit blind typically collect findings that a sampling exercise would have caught.
What the auditor asks to see
- Expediente del equipo — the per-equipment file, maintained for each item including Category I equipment
- Classification record placing each item in Category I, II or III under clause 7, based on relief-device set pressure, volume and whether the fluid is hazardous
- Registro de la última prueba de presión o exámenes no destructivos practicados a los equipos
- Resumen cronológico de las pruebas de presión o exámenes no destructivos
- Procedimientos for the pressure tests and non-destructive examinations, with the acceptance and rejection criteria applied to results
- Records signed by personal certificado endorsing NDT results, and by an engineer with knowledge in the matter endorsing pressure tests (clause 13.2 f and i)
- Dictamen de evaluación de la conformidad, or dictamen de evaluación de la conformidad con reporte de servicios where a Type C unit provided the services
- Aviso a la Secretaría for Category III equipment, filed within sixty days of the dictamen, together with the STPS-assigned número de control
- Registros de capacitación — theoretical and practical training records for workers who operate, maintain, repair and test the equipment (clause 17)
Findings to close before the audit
- Equipment misclassified into Category I or II to escape the Category III duties to have a unidad de inspección present and to notify STPS
- Only a volumetric examination performed, with no accompanying surface or flux-loss examination as clause 13.5 requires
- NDT results endorsed by a technician whose certification cannot be traced to NMX-B-482, its replacement, or a demonstrably equivalent scheme
- Pressure test endorsed by an NDT technician rather than by an engineer with knowledge in the matter, contrary to clause 13.2 f and i
- The five-year examination performed outside the sixty-day window before the end of the quinquennium
- Aviso to STPS not filed within sixty days of the dictamen, leaving Category III equipment without a número de control
- Chronological summary of pressure tests and non-destructive examinations missing from the equipment file
- A dictamen relied on beyond its validity — five years for used equipment, not the ten that applies to new
Related: the NOM-020-STPS overview, outsourced ASNT Level III cover, written practice development, NDT procedure development, a programme gap assessment, interim Level III cover.