3/4" - 1" Piping system for 93% sulfuric acid system 1

[AlbertaMecchie]

I have read that installing socket welded piping in a 93% sulfuric acid system is not recommended, I am wondering why this is.

Reason I ask is I am installing a 3/4" or 1" piping system and how practical is it to buttweld piping this small ? Or can I just go with socket weld ?

Thanks,

Jon

 

[EdStainless]

This size gets welded with semi-automatic orbital equipment all of the time.
Socket welds in acid service are discouraged because of the risk of crevices. (at least that what I have been told)

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P.E. Metallurgy, consulting work welcomed

 

[Rputvin]

Socket welds will have a gap at the bottom of the socket, as well as up the sides of the inserted pipe up to the weld. I'd imagine acid would settle in these areas.

 

[MJCronin]

Well...

According to these people, both socket welded and threaded pipe fittings are discouraged.

https://info.veolianorthamerica.com...industrial/sulfuric-acid-push-information.pdf

You could construct your small bore system from straight and bent Schedule 80 CS piping and Class 150 Flanges .... Tees may be a problem

As stated above, both socket welded and threaded fitting require a liquid "dead zone" as part of their design

Under dead zone conditions , a mechanism known as hydrogen grooving will occur where movement of hydrogen bubbles on a carbon steel surface removes a protective film and locally increases the corrosion rate. This is a common problem with older carbon steel piping and essentially is an erosion-corrosion mechanism. Hydrogen grooving will also cause corrosion along the sides and top of both piping and equipment.

Oxygen and iron can increase this effect.

Fluid velocity is your enemy ... keep the flowrate slow

In my opinion, all CS sulfuric acid piping (93 - 98%) should be inspected every 3 years and replaced about every 5 - 7 years

Also, I would not run any systems smaller than 1" NPS ....

BTW, for sulfuric acid systems in Nuclear Power Plants, the following configuration and material selection is recommended:

All Fittings 2" and Smaller
Type: Seamless Butt Weld Ends
Material: ASTM B366, Alloy 20Cb-3 (UNS N08020)
Schedule: 40S
Dimension: ASME B16.9
Max Temperature: 140F

MJCronin
Sr. Process Engineer