Difference between casting & forging 3

[Procurement2]

My client requires gate valve with wedge 316SS (forging) but my principal is offering CF3M (casting). Can any one advise me if I can accept this. My principal says performance is the same for casting & forging. They intend to use casting because of less cost. The specs is 6" gate valve with A351 CF3M Body/Bonnet, Trim 10

 

[hsbcn]

Cast iron is definitely not malleable; it's brittle. That's why there's a special product called "ductile cast iron" but tht's a relatively modern invention. On the other hand, steel is malleable- ask a blacksmith. It's easier to hammer to shape when it's hot but it can be done cold.

The twisted bits of iron used for railings and such are "wrought iron" which is actually pretty much steel. It doesn't help that there's more iron in steel than in cast iron. The nomenclature was dreamed up over the years before they really knew what they were doing.

Also, just about all the springs I have ever seen are steel, twisted into shape. Anyway, the question has been answerd cast metals are poured into shape; forged ones are pounded to shape.

My focus: Alloy Valves Duplex Valves Monel Valves Inconel Valves [link titanium-valves.com]Titanium Valves[/url] Hastelloy Valves

 

[hsbcn]

As for the CF3M vs. forged stainless steel, you should ask your customer whether they can accept the cast wedge. It's their choice, though there shouldn't be an issue for them to accept.

My focus: Alloy Valves Duplex Valves Monel Valves Inconel Valves [link titanium-valves.com]Titanium Valves[/url] Hastelloy Valves

 

[MikeHalloran]

The reason why one's principal might not accept a cast part is that a cast part may very well contain one or more internal flaws that could cause failure in service.

Internal flaws are likely to be discovered during the forging process, where the plastic flow induced by the forging hammer will probably open any flaw and make it visually detectable.



Mike Halloran
Pembroke Pines, FL, USA

 

[gerhardl]

The pressure, actual service and the 'branch experience' for valvetype and material selection would very much influence the choice. The requirement for forged material obviously has a (historical?) background. The experience with cast materials could be negative, perhaps for a particular brand? The requirement could also have been set a bit high, but anyway all consequences must be considered by a revision of a material/quality revision. The cost for failure is always higher than a smaller amount 'saved' for an altered single component.

 

[donf]

I would hope that your client has a better understanding of the particular application than your valve supplier...... but maybe not.

Perhaps your supplier could provide performance history for his product on the same, exact application.

As info - Within a given "family" of materials, depending on method of manufacture, there can be subtle differences in metallurgy, but significant difference in corrosion resistance. I have first hand experience with a particular application, where wrought 316L (ASTM A312 WP316L) or forged 316L (A182 F316L) will fail, whereas cast 316L (A351 CF3M) performs satisfactorily.

donf

 

[Procurement2]

I think if casting is asked for in the specs, then we can use forging. But if forging is asked for, then we cannot use casting. Am I correct.

 

[SJones]

Presumably, the purchaser is demanding an ISO 9001 certification of the supplier. In which case, the supplier is required to review the purchaser's requirements and resolve any discrepancies with the purchaser before committing to supply. The purchaser asked for a forging and expects to receive a forging, unless acceptance of a casting has been documented.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[PAN]

You should discuss with your customer about the CSL (Casting Specification Level). I understand that you can refer to API Spec 20A.

However, If I am your customer, I may stick with forging to minimize the risk.