PED impact test 316L

[Anna220284]

Hello All,
I have being working on a new design for a helium vessel 316L parent material with welding filler 316LSi. We have carried out the impact Charpy V test for a PQR at 77K following the design standard EN ISO 13445. Following this design standard we strongly believe we comply with PED as it is harmonised standard.
The NOBO is reviewing the WPQR and I have been told we should do the impact test at 4.2k as the minimum operating temperature.
I am getting stressed trying to give them evidence that such low T for impact test it is not required.
13345 clearly states 77K is the required temperature for impact testing for any design operating at <-105°C.
Anyone had similar experience with Notified Body?

 

[XL83NL]

Can you provide a bit more background on the application, like design temperature, material thickness, dimensions?
In general EN 13445 (there shouldn’t be ISO in there as ISO hasn’t adopted EN 13445) is a harmonised standard. Complying with it means compliance to the ESR’s of Annex I of the PED 2014/68/EU. Review the applicable annex ZA of any of the codes sections (e.g. EN 13445-2 for materials) and it should be clear how that section relates to the ESR’s.
(Un)fortunately I can’t tell from similar experience what to do, but I’d ask the nobo to show you which section, rule, paragraph or whatever you haven’t followed and should’ve followed instead.

Huub

 

If I know my conversion factors then 77°K = -196°C, which is the boiling point of nitrogen. Code impact requirements are conveniently designed around this temperature. This is about as low as you can go with the common austenitic stainless steels, and the problem is impact toughness of the weld deposit, not the base metal.

The process you select and the characteristic filler metals associated with them has the biggest bearing on successfully meeting Charpy requirements at -196°C. GTAW generally does well, but SMAW requires a basic flux coating that is distinctly user-unfriendly to the welder. You also want very low or zero ferrite in the deposit. Even then it can be hit or miss.

I would not expect 316LSi to withstand Charpy testing, because Silicon is a ferrite promoter in austenitic SS deposits. For GTAW, the preferred process, you do not need the fluidity that added Si offers, so stick with 316L.

4.2°K seems unbelievable, but then I have never had to qualify a PQR with that requirement.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[IdanPV]

Anna220284,

You may want to have a look at the PED Guidelines G-17 regarding approach that can be used to decide if a steel grade selected for a pressurized part requires specific impact properties.

 

[XL83NL]

Idan, if the OP uses a harmonized standard, he shouldn't be concerned about the guidelines. Though the guidelines are an excellent addition to the PED, the harmonized standard in this case will be much more useful than a guideline. Hope the OP returns and provides feedback as to why the NoBo requires 4.2K impact test, and which section of EN 13445-2 requires this.

Huub

 

[DriveMeNuts]

As the vessel is operating at 4.2K, why wouldn't you impact test it at that temp? (i.e. what is the basis of the code not requiring it.)
I have worked on a helium recover vessel where we did this. It was non-EU and we were following the customer's specs.

 

[XL83NL]

The OP didn’t (specifically) mentioned that 4.2K is the vessels operating temperature.

Huub

 

[Anna220284]

Thank you all for all your replies.

At the end, we are going to proceed with a new WPQR including impact test at 4.2K as the minimum operating temperature is 4.2K and new filler specific for cryogenic application with FN =3

 

Let us know your Charpy results.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[XL83NL]

agreed with IM, let us know the results.

Huub
- You never get what you expect, you only get what you inspect.