Between 2022 and 2025 I built a hydrostatic gas cylinder testing laboratory from an empty room, took it through ISO/IEC 17025 accreditation and then ran it for three years. This guide is the overview I wish I'd had at the start: what accreditation really requires, in what order to do things, and where labs usually lose time.
It is a practical guide, not a substitute for the standard itself or for your accreditation body's specific requirements. Always work from the current editions of the documents that apply to you.
What ISO/IEC 17025 accreditation means
ISO/IEC 17025 is the international standard for the competence of testing and calibration laboratories. Accreditation against it means an independent accreditation body has assessed your lab and confirmed three things: that you are competent to perform specific tests, that you work impartially, and that you operate consistently, so a result today means the same as a result next year.
The important word is specific. You are never accredited "in general". You are accredited for a defined scope: particular tests on particular items to particular standards. When your national accreditation body is a signatory to the international ILAC arrangement, results within that scope are more readily accepted in other countries.
For a cylinder testing lab, the stakes are concrete: a cylinder you pass goes back into service under high pressure. Accreditation is how you prove that your pass and fail decisions can be trusted.
Step 1: define your scope
Everything else depends on the scope, so decide it first and keep it realistic. Ask:
- Which cylinders? For example seamless steel, aluminium alloy, welded steel or composite. Each type has its own inspection requirements.
- Which tests? Hydrostatic pressure testing, visual inspection (internal and external), thread inspection, and other checks your standards require.
- Which standards? Periodic inspection and testing of cylinders is governed by product standards. Internationally, ISO 18119 covers periodic inspection and testing of seamless steel and seamless aluminium-alloy cylinders; many countries also have national standards. My lab's accredited scope included the Iranian national standard INSO 6792.
A narrow, well-executed scope is better than a wide one you can't support with equipment, procedures and trained staff. You can extend the scope later.
Step 2: plan the layout around the workflow
Design the lab around the path a cylinder takes, so items never cross back and tested cylinders can't be confused with untested ones. A typical flow:
- Receiving and identification: log the cylinder, its markings and its owner.
- Depressurisation and valve removal: safely, in a ventilated area suitable for the gases involved.
- External and internal visual inspection: good lighting and the right tools to see inside.
- Cleaning, where the procedure requires it.
- Hydrostatic test bay: with a protective enclosure, because you are working with high pressures.
- Drying, valve refitting and marking of cylinders that pass.
- Quarantine for rejected cylinders, clearly separated and labelled, so they cannot re-enter service by mistake.
Also plan storage for records, a controlled environment for equipment that needs it, and enough space to work safely.
Step 3: equipment and calibration
Choose equipment to match your scope and the methods in your standards. Typical items for hydrostatic testing include a high-pressure test pump, pressure gauges or transducers, the expansion measurement system, a weighing scale, thread gauges and inspection lighting. Depending on scope, ultrasonic wall-thickness measurement may also be needed.
For accreditation, the equipment itself is only half of it. Every instrument that affects a result needs:
- Calibration traceable to national or international standards, from a competent calibration provider.
- A calibration programme with intervals, and records of every calibration.
- Intermediate checks between calibrations where needed, to catch drift early.
- Clear identification, so you can always tell which instrument was used for which test.
How the hydrostatic test works
In a volumetric expansion test, the cylinder is filled with water and pressurised to its specified test pressure. The cylinder expands slightly under pressure. The total expansion is measured at test pressure; after the pressure is released, any expansion that remains is the permanent expansion.
The ratio of permanent to total expansion shows whether the cylinder wall still behaves elastically. The applicable standard sets the acceptance limit; for many steel cylinders, permanent expansion must not exceed 10% of total expansion. A cylinder that exceeds the limit, leaks, or shows unacceptable defects in visual inspection is rejected.
Every step of this, from test pressure to readings to the decision, must be recorded so the result can be traced and repeated.
Step 4: build the quality system
ISO/IEC 17025 (2017 edition) is organised into general, structural, resource, process and management system requirements. In practice, your quality system needs to cover:
| Area | What you need in place |
|---|---|
| Impartiality and confidentiality | How you identify and manage risks to impartiality, and protect client information. |
| Structure | Who is responsible for what, and who authorises results. |
| Resources | Personnel competence, facilities and environment, equipment, metrological traceability, external suppliers. |
| Process | Review of requests, selection and verification of methods, handling of test items, technical records, measurement uncertainty, ensuring validity of results, reporting, complaints, nonconforming work, control of data. |
| Management system | Document and record control, risks and opportunities, improvement, corrective action, internal audits and management review. |
The trap is writing a thick manual copied from a template. Assessors check whether your documents match what your staff actually do. Write procedures for your lab, test them on real work, and simplify them until people follow them.
Step 5: people and competence
An accredited lab is only as good as the people doing the tests. For each role, define the competence required, train people against it, assess them, and keep records showing who is authorised to do which test. Keep training records current as procedures change.
Safety training belongs here too: high pressure, gas residues, and lifting and handling heavy cylinders are real hazards.
Step 6: the accreditation process
Details vary by accreditation body, but the path usually looks like this:
- Run the system first. Operate under your quality system for a period, so you have real records to show.
- Internal audit and management review, covering the whole standard.
- Application to the accreditation body, with your documents and proposed scope.
- Document review and on-site assessment, including witnessing tests.
- Closing findings: nonconformities must be corrected with evidence.
- Accreditation decision, followed by regular surveillance assessments.
Accreditation is not the finish line. Surveillance means the system has to keep working every day, not only before an audit.
Common mistakes to avoid
- Too wide a scope at the start, which multiplies the equipment, procedures and competence you have to prove.
- Procedures nobody follows, copied from a template and disconnected from real work.
- Calibration gaps: an instrument out of calibration on the day it was used puts every result from that day in question.
- Incomplete technical records that don't let you trace a result back to the cylinder, equipment, calibration and person.
- Weak segregation of rejected cylinders.
- Treating the audit as the goal rather than the daily operation.
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