PED - Impact Test Requirements 1

[Graybags]

Hi,

Is there a need to impact test Nickel Aluminium bronze material to satisfy the PED?

Annex 1 sestion 7.5 states that a steel is sufficiently ductile if its bending rupture energy measured on an ISO V test-piece is no less than 27J at a temperature not greater than 20 deg C but not higher than the lowest scheduled operating temperature.

Guideline 7/17 reads as follows:-

Q) Shall a steel grade selected for a pressurized part always have specified impact properties?

A) Yes, the only exception is ductile materials which are not subject to ductile/brittle transition at the foreseeable conditions the equipment will be exposed to.

The component i'm designing is a pressurized valve body with a minimum working temperature of -20 deg f.

Is nickel aluminium bronze sufficiently ductile? Will these materials exhibit ductile/brittle transition at this temperature?

I'm really scratching my head with this one. I asked the same question to my notified body months ago and cannot get an answer from them.

Any advice would be very appreciated.

Regards,

Graham

 

[bcd]

Graham,

The PED is mainly intended for carbon steels that can exhibit a rapid transformation from a ductile material to a brittle material. No, nickel aluminum bronze does not exhibit brittle behavior in most applications. It is commonly used down to -190 C (liquid nitrogen). No need to perform an impact test for PED. But for PED, you will need a PMA that confirms it remains sufficiently ductile down to the temperature rating you allow your product to be used. How you do this is between you and the notified body. Impact testing every casting lot or heat is not necessary if your valve temperature rating is well above the material transition temperature.

bcd

 

[BVMan]

BCD do you (or anyone else) have any thoughts on F316 or CF8M. Some of our Suppliers say that they cannot supply valves in these materials below -29 deg C without carrying out Charpy Impact Testing.

Yet I have seen another manufacturer who makes the statement that their valves CF8M / F316 Valves are suitable down to -196 Deg C but do not offer any Charpy Results on their Material Certs.

They even allow Valve Modification Houses to etch out "-29" on their Nameplates, fit a Cryo Extension and Re-Mark as "-196".

 

[bcd]

BVMan,

The ductility of austenetic stainless steel remins relatively constant down to cryogenic temperatures. It does not exhibit the radical transition in ductility that carbon steel can exhibit. In practical terms, there is no reason to pay for the cost of impact testing because it should pass without any problems. Carbon steel will also easily meet PED impact requirements provided the chemistry and heat treatment are correct. It is a waste of $ to impact test F316 / CF8M.

BCD