ASTM A312 or A778 corrosivity

[mae1133]

Generally speaking, does ASTM A312 or A778 provide better protection against corrosion. I have no specific application, but just trying to determine the main differences between the two standards for 304L/316L SS piping as related to corrosion.

 

[EdStainless]

A778 will always be inferior to A312 because it is unannealed.
As you go to higher alloys (316L, 317L, and so on) the lack of annealing will result in more difference between the base metal and the welds.
The risk of selective weld corrosion in A778 is very real.
In stabilized alloys (321 and 347) the variation should be less.

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P.E. Metallurgy, consulting work welcomed

 

[mae1133]

So, overall, would you consider pipe manufactured to ASTM A312 to be superior to A778. I am tabulating some of the differences as follows, based on what I have found:
• A312 is commonly used higher temp and higher pressure applications such as steam boilers, pressure vessels, etc.
• A312 has higher mechanical strength than A778,
• A312 has better weldability due to lower carbon content,
• A312 contains chromium-nickel alloy vs the less expensive titanium in A778. (this one seems wrong to me. One of the issues in going by what you find on the internet),
• A312 is only produced as seamless or welded pipe while A778 is only produced as welded tubing,
• A312 requires pickling,
• A312 has post annealing where A778 does not,
• A778 generally has a wider range of diameters.
Please let me know if any of these are not accurate. Again, no particular application, but just looking at general differences and thanks for your input.

 

[EdStainless]

2, 3, and 4 are wrong, the alloys are the same so the properties will be the same.
The bulk of A312 is welded so I don't know that that matters.
Seamless sill holds a position for high temps or very heavy walls.
The pickling (or bright annealing) is part of the annealing and finishing process, and part of achieving the alloys optimal corrosion resistance.
The largest A312 that I ever made was 48", but not many mills can anneal the large sizes.
And with thin walls annealing large sizes can be the biggest PIA that there is, they won't stay round.
Offhand I don't recall the NDT requirements in A778. Look into that.

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P.E. Metallurgy, consulting work welcomed

 

[mk3223]

What's the service of the A778 SS piping in your application?
The "better" corrosion property of A312 vs A778 piping may be determined by the suitable process application with the factor of the material cost involved.