SS 316 for Vent line 2

[bck2ftr]

We have a 3/4" vent line from equipment of SS304 (300#) material as per P&ID. After the Isolation valve (3/4") there is a spec break shown. The next specification stands for SS316 (150#) material. I want to clarify a doubt here. Why did the process engineer chose SS316(150#) instead of SS304(150#).
NOTE: Spec break is right after the socket welded isolation valve. i.e. on a welded joint

 

[EdStainless]

It could be that the outer portion of the vent line in subject to humid air (if it is an open vent).
The moisture could make it more subject to corrosion.

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Plymouth Tube

 

[poli60]

I share EdStainless point about moisture corrosion... but I don't see a big difference between 316 and 304.
Maybe this is forced by the plant specific piping classes/specifications.

 

[poli60]

http://www.cheresources.com/invision/topic/20120-304-ss-vs-316-ss/#entry83160

 

[Ripz]

There no reason for using the 316L. Unless as Poli said, that it was forced due to Plant piping specs.

Sure 316 more corrosion resistant, but if it's venting to atmosphere, the 304 would have been more than adequate and less costly.

Sounds like your Process Engineer should have consulted a Mechanical Engineer.