Passivation of 316L in 98% H2SO4 service at ambient temps 1

[JonD71]

Hello all

Am currently replacing a 98% H2SO4 carbon steel line running at ambient temp around 40 deg C with 316L. The line is approximately 200 meters long and 250mm diameter. As such it has multiple welded joints. The question is do I need to passivate this line internally to give me additional corrosion resistance or will the sulphuric acid internally in hte pipe passivate itself and reinstagate a passive layer around the welds etc.

Additionally the line is made from seamed pipe not seamless. Though this is acceptable under our pipe specification onsite the main reason the line has been changes is due to internal flow in duced corrosion of the initial carbon steel line and to take advantage of 316L's better flow rate in this service.

Regards

JonD71

JonD 71
Australia

 

[unclesyd]

When you have SS in a corrosive media such as your case a passivation procedure is of little value in staving off the inevitable loss of metal. SS doesn't form the protective film as does the CS. H2SO4 doesn't passivate SS.

Our experience has been very mixed in handling H2SO4 in 316/316L. One thing we did find that acid purity was factor in determining the corrosion rate of 316/316L

Someone should come back with some of the new alloys that are much better for handling H2SO4.

 

[JonD71]

Thanks again uncylesyd

Looks like we wont be boterhing to pasivate the line internally. Though have completed local passivation externally of welded joints.

Regards

JonD71

JonD 71
Australia

 

[metengr]

unclesyd/JonD71;
In situations where we had experienced high flow rates with concentrated sulfuric acid (minimum 93% at ambient temperature) we upgraded from 316SS to Carpenter 20Cb-3 SS.
Other choices include; 20Mo-3 and 20Mo-4

Here is the web site for Carpenter stainless steel alloys suitable for sulfuric acid;

http://www.cartech.com/

 

[EdStainless]

Alloy 20 is the better option for this service.

There should be no problem with welded 316 if it was annealed properly. Did you buy it to A249? If so you should specify that it must pass the S7 Weld Decay Test. This will give you low residual ferrite in the welds.
You need to make sure that you field welds have controled ferrite levels and good ID profile.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm