316 SST vs 316L SST; Corrosion Resistance

[valvepuke]

We are seeing specifications requiring 316L SST for machined parts in valves, etc., to be used in some corrosive services. We have, in the past, generally utilized only 316SST. There is no welding required for such parts. My questions addresses the difference in corrosion resistance between 316 and 316L.

I would appreciate a quick lesson on these two versions of stainless steel.

 

[jbeckhou]

See link

http://en.wikipedia.org/wiki/AISI_steel_grades

Petrotrim Services

 

[MikeMet]

If the Type 316 sst part is properly and fully solution annealed, there should be no real difference in corrosion rate between the L-grade and non-L grade in most processes. There could be some difference in oxidizing acids that cause intergranular corrosion.

 

[SaeidNorouzi]

the higher Carbon content in 316 can cause intergranular corrosion. because Carbon absorb Cr near grain boundaries. But in 316L due to having lower content of C the probability of formation of Chromium carbide decreases.
For both alloys carrying out solution heat treatment increases corrosion resistant considerably.

 

[valvepuke]

Thank everyone for your replies so far. I see now that 316L is more corrosion resistant than plain 316.

The fluids we handle the most are lean amines (45%amine, 55% water), rich amines, containing H2S and CO2. I would assume that our clients are considering 316L to be better for this service. We also handle hydrocarbon gases also having H2S and CO2.

Further comments would be welcome.

 

[EdStainless]

In the fully annealed condition there is no difference in corrosion resistance. You will only see an advantage to using 316L when you weld and cannot solution anneal afterward.

That said, if you are getting metal that originates in the US, Canada, Japan, or northern Europe then virtually everything will be 316L. In order to get higher carbon you would need to order 316H.
However for metal melted elsewhere it might be a different story.
There should be no price premium for 316L.
And there is safety in using it.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[unclesyd]

316L SS had one very definite advantage if there is ever any weld repair needed. The valve body can be repaired without a solution anneal.

All our valves in Nitric/Organic service are 304L for this very reason. In the secondary processes where we have to switch to 316 SS we also use 316L for repair purposes.

 

[Guest102023]

I concur with Ed & unclesyd.
L grades are now more available and often lower cost.

 

[moltenmetal]

Better still, dual grades meeting both the strength of the straight grade and the low carbon of the L grade are now available at virtually no cost premium. Benefits of both at no cost- what's not to like?

 

[blacksmith37]

I expect the mills miss the "good old days" when < 0.035%C was premium L grade and heats > 0.04%C were premium H grade.They could hardly miss a price extra.