Valve's trim in H2SO4 service 4

[afarboudi]

Hi
In H2SO4 services (98% - 85c) the contractor want to use PTFE as body seat ring and trim but we think it is not proper. also we have another choice, carbon steel. but seems high corrosion will be happened in aforementioned temperature.
could you please help me to select the best choice.

 

[metengr]

What type of valve and valve body material?

 

[afarboudi]

Globe valve, Body material is A105

 

[moltenmetal]

Carbon steel is ONLY resistant because it forms a layer of ferrous sulphate on the surface. Even MODEST velocities will destroy that surface layer and the parent material will be destroyed rapidly. A carbon steel plug in a globe valve would be eaten like candy.

Alloy 20 has a hope, but I'm not near my references. You'd need to review the NACE sheets and see what it says for pipe- then increase the alloy selection in the direction of additional resistance because you're dealing with material exposed to high velocity and potential erosion-corrosion.

 

[metengr]

Alloy 20 would be the choice under the stated conditions. You can also use the attached as a guide;

http://globalsupplyline.com.au/wp-content/uploads/2014/10/Valve_chemical_resistance.pdf

 

[EdStainless]

And I hope that you are looking at a high Si Stainless for the piping.
Even though 98% acid isn't all that corrosion resistant the combination of high temp and flow make this a delicate application.
You need to own a copy of MS-1 on Sulfuric acid and Oleum printed by MTI.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

That A105 body will be toast in no time. Not only the trim need to be A20- the body does too.

 

[MJCronin]

Please bear in mind that Alloy 20 was developed specifically for sulfuric acid service. If carbon steel could sustain this service, Alloy 20 would probably not exist.

http://www.rolledalloys.com/alloys/nickel-alloys/alloy-20/en/

Since this seems to be your first acid system, and since Alloy 20 is expensive in a huge globe valve, perhaps this large, expensive type of valve is not your best choice...???

Consider the use of butterfly valves for flow control and plug valves for on-off control.

XOMOX Series 9000, or the cheap Chinese knock-off, may be a good choice .....

http://www.sulphuric-acid.com/techmanual/strong acid/sa_valves.htm

Like most of these posts, we never get enough information without asking several times ...

What is the strength of the H2SO4 ????

MJCronin
Sr. Process Engineer

 

[afarboudi]

Tanx guys, thank you so much

 

[moltenmetal]

The size hasn't been mentioned, but if it's "huge", the all-lined Xomox or Durco plug valves are a good option. We've fitted them with gear operators and find them adequate for coarse control. They will be corrosion immune, which in this service beats mere corrosion resistance hands down.