Impact Tests for Stainless Steel

[curiousguy]

Hi,
We are establishing a procedure for stainless steel to EN 15614. My company hasnt worked to EN standards before so we are confused as to whether the impact testing requirements for procedure qualification as per EN 15614 apply even to Stainless steel. If it is not required, which standard exempts impact test requirements for SS?

[nnreddy]

Hi,

If you are establishing WPS & PQR as per En15614 to meet the EU Standards you must do impact testing even though SS will easily pass impact testing.

Regards
NNREDDY

[curiousguy]

What temperature should I choose for the test & where can I find the impact values that need to be satisfied?

[mariog]

Because you are a curious guy, I suggest you to take a look in 13445-2 Unfired pressure vessels - Part 2: Materials, especially B.2 Material selection and impact energy requirements

You can find out there tables that list steels taken from harmonized European material standards with specified impact properties below –10 °C.
Every harmonized European steel standard has specified impact properties, so you just have to identify the harmonized European standard covering your application.

You have to correlate your design reference temperature TR (i.e. the temperature used for determining the impact energy requirements, determined by adding the temperature adjustment TS to the minimum metal temperature TM: TR = TM + TS) with impact test temperature TKV (i.e the temperature at which the required impact energy has to be achieved).

The methods specified in B.2.2 (method 1) or B.2.3 (method 2) should be used to determine the impact energy required to avoid brittle fracture. Alternatively, B.2.4 (method 3) may be used to determine the required toughness.

I suggest you also to take a look to Guideline 7/17, answering to Question: What approach can be used to decide if a steel grade selected for a pressurized part requires specific impact properties

[link Point to another website Only the registered members can access]
Regards.

[mariog]

Remember what NNREDDY told you:
"If you are establishing WPS & PQR as per En15614 to meet the EU Standards you must do impact testing even though SS will easily pass impact testing."
The point is 316L is a very good material for low temperature. All the rest is a puzzle with formal requirements.

[curiousguy]

We are using ASTM A 316L to establish the procedure. Can I use the values specified for an equivalent material like 1.4404 or 1.4432?

[mariog]

Yes, 1.4404 it’s worldwide recognized as "equivalent" with 316L.
In fact 316L is the low carbon version of 316 and is quite immune from grain boundary carbide precipitation; for this reason it’s used extensively for weldments where its immunity to carbide precipitation due to welding assures optimum corrosion resistance.
The austenitic structure also gives to this grade excellent toughness, even down to cryogenic temperatures.

As I know, 316L is not subject of any approval by European Approval of Materials (EAM), so probably, working strictly under "PED", you need to issue a PMA- Particular material appraisal, that is the process by which the pressure equipment manufacturer ensures that each proposed material that is not in a harmonized standard or covered by a European Approval for Materials (EAM) conforms to the applicable Essential Safety Requirements (ESR) for materials.

[curiousguy]

We are not establishing this procedure for any particular job. Will this procedure still be valid for welding 316L for a job that requires WPS/PQR to be qualified as per PED? Or would it still require the PMA to be done?

[mariog]

I’ll quote the following document, hoping this one will help you...

[link Point to another website Only the registered members can access]
"As required by the Pressure Equipment Directive 97/23/EC (PED) Annex I section 4.2, the pressure equipment manufacturer is responsible for preparing documentation for materials to be used for pressure equipment in categories I to IV. For pressure equipment in categories III and IV this documentation is submitted to the Notified Body in charge of the conformity assessment for the equipment so they can perform an appraisal of the particular material with regard to the pressure equipment, the intended use and applicable design rules.
[……]
Decisions made concerning a specific material for use in a specific sets of conditions, do not need to be repeated. However, manufacturers and where applicable notified bodies must ensure the PMA is suitable for its application and that this is recorded in the technical documentation.
Pressure equipment manufacturers may utilise PMAs prepared and supplied by another manufacturer, e.g. the manufacturer of an assembly, on condition that the PMA is reviewed and adopted by the PE manufacturer and where applicable the NB in charge of the conformity assessment procedure, to ensure accuracy of the document and suitability for the application.”

I understand you are trying to perform a general document; however it will be a day when you’ll need to present to Notified Body all necessary documents, including documents for materials used (particularly a PMA, if any).
As you can see, PMA is not viewed as a "general" document until the first approval and normally, PMA is related to a specific job. After approval, PMA gets a kind of generality, as you can see above.

And quite strange, Notified Body cannot perform a PMA as a general document..
Guideline 7/21 Question: May a notified body perform a particular material appraisal at the request of a material manufacturer? Answer: No. The PMA is performed on request of a pressure equipment manufacturer.


About impact testing of 316L, it is worth to consider paragraph 2 of Guideline 7/17
The exception concerns “ductile materials which are not subject to a ductile/brittle transition at the foreseeable conditions the equipment will be exposed to”.
Examples of such materials are: austenitic stainless steels.
But once again, it’s up to Notified Body to consider or not your particular case as "exception"…

[curiousguy]

Thanks a lot mariog. I ll suggest this to my senior at work.

[mariog]

You are welcome.
The last advice I can give you is: Don’t expect Notified Bodies’ specialists have a high engineering qualification and knowledge. In some cases, you risk to be deeply disappointed… Of course there are also pleasant exceptions.

[curiousguy]

What I understand about Impact testing for stainless steel is that it is required if the design requires it to be done for the particular job. If a particular vessel is designed using SS materials without specifying impact properties it can be welded by employing a procedure that is not tested for impact values. Am I right with this one? or am I way off?