← Back to Blog

What Should You Check When You Audit a Ball Valve Factory?

Why does a factory tour prove less than it appears to?

Sourcing guides repeat a reassuring line: certificates can be forged, but production capability and a test laboratory cannot be faked on the day of an audit. That is true, and it answers the wrong question.

A test bench on the floor shows that the factory can pressure test a valve. It does not show that the valves in your shipment were tested at the pressure you specified, held for the duration the standard sets, and read on a gauge that was in calibration. A spectrometer in the laboratory shows the factory can analyse a heat. It does not show that the heat your bodies were poured from was analysed, or that the certificate you received belongs to that heat.

You are buying practice. A tour shows capacity.

The two also run in opposite directions. A tour goes forwards, from raw material to packing, along a route the host chooses. A trace goes backwards from a part the auditor picks, and it stops wherever the evidence stops.

What should you ask for at each station?

The table below is the trace in order. The middle column is what a working system produces without being asked twice. The right column is what a break looks like in practice. A single break is a finding, not a verdict. A pattern of them is a verdict.

Run the trace on two valves, not one. Pick the first from packed stock whose paperwork is already filed. That tests the archive. Pick the second from today's line. That tests whether the live process writes the records as it runs, or whether they are assembled afterwards for whoever asks. A factory that can do the first and not the second has a filing system rather than a traceability system.

Station 1 decides whether the rest is possible. If the finished valve carries no mark that ties it to a lot, the trace cannot start from the part and has to start from a document the host hands you, which is the tour again. Marking is covered in what the markings on a ball valve body mean.

What does ISO 9001 oblige a factory to keep, and where does it stop?

If the factory holds ISO 9001, four clauses of the 2015 edition map directly onto the trace. Reading them tells you which records a certified factory has to keep and which it only keeps if asked.

Clause 8.5.2 is the one that surprises buyers. The traceability it covers is conditional. A factory can hold a valid ISO 9001 certificate, identify its valves by type and size only, and be entirely within the standard, as long as no requirement for traceability has been set. If you want a valve tied to its heat, the purchase order has to say so. Writing EN 10204 3.1 with the heat number traceable to the part on the order turns clause 8.5.2 on for your parts. How to read what an ISO 9001 certificate actually covers is set out in what a valve manufacturer's certification actually proves.

One timing note. ISO 9001:2026 was published on 16 September 2026. Certificates issued against the 2015 edition stay in circulation through the transition period, and the clause numbers above are the 2015 ones. Check which edition is printed on the certificate in front of you.

Why is heat treatment the station a tour walks past?

For CF8M, ASTM A351 sets a solution treatment at 1040 °C (1900 °F) minimum, followed by a water quench or rapid cooling by other means. The treatment takes carbides formed during solidification back into solution, which is what restores the corrosion resistance of the cast grade. The mechanism is covered in whether CF8M is the same as 316.

None of it is visible on the finished valve. A body that went through the furnace at temperature and a body that was pulled short look the same, measure the same and pass the same shell test. The only evidence is a record: the furnace chart or log for the load that held your heat, with time at temperature and the quench.

Two questions get to it. First, show me the record for the load that contained the heat in the valve I picked. Second, how do you know the whole load reached temperature, not just the thermocouple? Aerospace and automotive supply chains answer the second one with defined pyrometry: AMS2750 and the AIAG CQI-9 heat treat assessment both cover temperature uniformity surveys and system accuracy tests on the furnace. Both are sector requirements, and a plumbing or general industrial valve order carries them only if the buyer writes them in. The question is still fair. The answer will be the factory's own method, and you want to hear what it is.

If the anneal is subcontracted, it is an external process under clause 8.4, and the record sits at the heat treater. Ask whether the factory holds a copy for your heat or would have to request it.

What should you watch during a live pressure test?

Ask to see a test run rather than a test record. The record tells you what was written down; the run tells you how it is done.

Under API 598 the shell test is made with the valve ends closed and the ball part open, so the body cavity is pressurised along with the ends. The pressure is 1.5 × the valve's rating at 38 °C, which is 30 bar for a Class 150 valve. The high-pressure closure test then runs at 1.1 × the rating, 22 bar for Class 150, with the ball closed and the downstream side open to view. Minimum durations scale with valve size and are tabulated in what API 598 actually tests.

Things to watch:

• The gauge number on the bench, written down and checked against the calibration register afterwards.
• Whether the hold is timed or judged by eye.
• Where the operator is looking during the closure test. Seat leakage appears on the downstream side, so that is where attention has to be.
• The ball position during the shell test. A fully closed ball leaves one side of the cavity out of the test.

Which two places does a tour usually skip?

The nonconforming area

Clause 8.7 covers how nonconforming output is identified and kept from being used or delivered. Physically, that should be a place: a rack, a cage or a marked floor area holding tagged parts. A foundry pours castings that fail, and a machine shop makes parts that miss, so the area is expected to have something in it.

Ask to see it and read three tags. Each should state what was wrong, who decided, and what happens next: rework, scrap, or use-as-is with a concession. The tags tell you what fails in this factory, which is information that is not in the brochure. Then ask for the most common rejection reason over the last month and the record behind the answer.

The external provider list

A trading company and a manufacturer can host an identical showroom. The difference shows up in the external providers, which clause 8.4 obliges a certified factory to control. Ask for them as a written list before the visit, and ask which of casting, heat treatment, surface treatment and seat moulding are done on site. Anything on the list is a site you have not audited, and what changes when that site changes is covered in what has to be re-qualified when you change valve supplier.

For a buyer comparing a stainless steel ball valve OEM manufacturer against an agent, this list is the document to read first, because it states in writing which stations of the trace belong to the factory you are standing in.

How do you run the audit in one day?

1. Before the visit, send the drawing revision you will order against, and ask for the external provider list and the calibration register. How quickly both arrive is itself information.
2. On arrival, choose two valves yourself: one from packed stock, one from today's line. Do not accept valves selected for you.
3. Trace the stock valve backwards through all seven stations, writing down the document reference found at each one.
4. Watch a live shell and closure test, note the gauge number, and check it against the register.
5. Read the furnace record for the heat in the stock valve, and ask how furnace uniformity is verified.
6. Follow the second valve through the stations it has already passed today, and confirm the records exist now rather than at the end of the shift.
7. Visit the nonconforming area and read three reject tags.
8. Close by listing each break in the chain with the record that was missing, and agree a date for the factory's response.

Checks that can be done from a desk, such as confirming a certificate number on the issuing body's register, belong before the visit and are listed in sourcing ball valves from Taiwan. The audit day is for evidence that cannot be emailed.

What can one audit day not show you?

Two valves on one day are a sample of the system on that day. The audit establishes a baseline. It does not detect drift, a change of foundry six months later, or a new seat supplier. Those need a change notification clause in the supply contract covering casting source, heat treatment, seat material and machining route.

The audit does not see inside the casting. Subsurface porosity needs radiography or a sectioned sample, and whether that is specified is a purchasing decision rather than an audit finding. The options are in what casting quality does to a ball valve.

It does not audit the subcontractors. Every site on the external provider list is outside what you saw.

And it says nothing about how the seats behave after two years of thermal cycling in your system. That is a qualification test on the product, run separately.

Frequently Asked Questions

Does ISO 9001 certification mean a valve factory has heat-number traceability?

Not on its own. Clause 8.5.2 of ISO 9001:2015 applies unique identification of outputs when traceability is a requirement. A certified factory can run without valve-to-heat traceability until the purchase order, a product standard or its own system makes traceability a requirement.

How many valves should be traced during an audit?

Two, chosen by the auditor. One from packed stock whose paperwork is already filed, which tests the archive, and one from the current day's production, which tests whether the live process generates the records as it runs.

Is a handheld PMI reading enough to confirm CF8M?

It confirms the alloying elements, such as chromium, nickel and molybdenum. Portable XRF does not read carbon, so it cannot separate CF8M (0.08 per cent carbon maximum) from CF3M (0.03 per cent maximum). The carbon figure has to come from the EN 10204 3.1 certificate for the heat or from an optical emission test.

What is the difference between a factory audit and a pre-shipment inspection?

A pre-shipment inspection checks one lot against the order. A factory audit checks whether the system that produces every lot generates the evidence it claims to. An audit that passes does not remove the need to inspect lots, and a lot that passes says little about the next one.

Can a third-party inspection company run the audit?

Yes. Give the inspector the drawing revision, the grade and the test standard on the order, and ask for a backward trace on named valves rather than a generic checklist, otherwise the report will describe the facility rather than the evidence behind a part.

Published by LINS Valve Industrial Co., Ltd., Taichung, Taiwan. Last Updated: 2026-09-24