Is Alloy 218 better than SS316?

Alloy 218SS316 in strength and pitting resistance, but it comes with a higher cost. Your choice depends on performance requirements, operating environment, and budget.

 

 Overview of Alloy 218 (Nitronic 50) and SS316

	Alloy 218 (Nitronic 50)	SS316
	S20910	S31600
	ASTM A182, A240, A276, A312, A479	ASTM A182, A240, A276, A312, A479

 

Alloy 218's higher chromium, nitrogen, and manganese give it superior strength and pitting resistance compared to 316.

	Alloy 218 (Nitronic 50)	SS316
C	<= 0.06%	<= 0.08%
	20.5–23.5%	16.0–18.0%
	11.5–13.5%	10.0–14.0%
	1.5–3.0%	2.0–3.0%
	4.0–6.0%	<= 2.0%
N	0.20–0.40%	<= 0.10%

 

Alloy 218 has ~80% higher yield strength than 316, meaning it can handle higher loads and stress with less deformation.

	Alloy 218 (Annealed)	SS316 (Annealed)
	~ 690 MPa	~ 515 MPa
Yield Strength (0.2% offset)	~ 380 MPa	~ 205 MPa
	~ 35%	~ 40%
	~ 217	~ 150–160

 

Is Alloy 218 magnetic?
In annealed condition, it is non-magnetic, similar to SS316.

 

In terms of corrosion resistance and pitting resistance, a clear comparison can be made using the Pitting Resistance Equivalent Number (PREN): the PREN of Alloy 218 is approximately 34–36, while that of 316 stainless steel is around 25–27. This result indicates that Alloy 218 has significantly better resistance to chloride pitting than 316 stainless steel, making it more suitable for environments prone to chloride corrosion such as seawater, brine, and chemical processing applications.

 

 

In terms of cost, Alloy 218, due to its alloying elements and lower supply, is priced at 2-3 times that of SS316; while SS316 is more economical and widely available in the global market.

 

Can Alloy 218 replace SS316 in all cases?
Not always. It's over-engineered for mild environments where SS316 suffices.