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sulfuric Acid corrosion to stainless steel

Current question and answers:

Q. I am considering injecting 93% sulfuric acid at 0.1 gpm into a 2" water line at 25 gpm. The line is 316L stainless and injection quill is CPVC. I am aware that 316L has good resistance to high concentrations (>80%) as well as low concentrations (<10%) sulfuric acid. The acid will be diluted from 93% to less than 1% at the injection point. Once fully diluted the corrosion will be insignificant. My only concern is the potential for corrosion around the injection site. Heat evolved should be very little, at most water temperature will rise from about 80 to 82 °F. The acid will only be injected for 2-3 days. If successful in controlling process pH, permanent lined piping may be installed for long term use at the injection site. I want to avoid the installation of lined pipe for this short term test if possible. Is lined pipe necessary for this trial or will 316L hold for such a short term application? I have looked on iso-corrosion curves and between 30-70% the corrosion increases greatly, so much so that the curves drop off the chart. I also understand that iso-corrosion curves are created from simple coupon tests and not actual operating conditions. Any insight would be very much appreciated.

Mike Smith
- Greenville, North Carolina, US
October 15, 2013

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⇩ Closely related postings, oldest first ⇩

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I am trying to find the best corrosion resistant pipeline to use as a drain for 98% sulfuric acid which has been flushed out with water. 316L is currently in use but is eating away rapidly.

Gavin P [last name deleted for privacy by Editor]
- Mt Isa, Queensland, Australia
2002

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2002

Hi Gavin,

sulfuric behaves differently at different concentrations. Stainless should be OK at low concentrations and even mild steel should be A.OK at very high concentrations.

Hence your given 98% concentration is something I'm looking at with a jaundiced eye! You might well have 98% or more in a line BUT, BUT, BUT just allow some air to get in there and the sulfuric will suck up all the moisture and REDUCE its concentration to deadly limits for many metals.

I believe that the German TROVIDUR PVC is OK at r.t. for 98% but ordinary PVC pressure pipe should last till the cows come home for 93%... at least it did for me and even welded PVC tanks for 93% will last a coons age, 16 years for sure.

There are other but more expensive plastics you could use. Perhaps CPVC. Certainly PVDF. Then there are the weldable fluorocarbons. I hope that this will help you somewhat.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

Can you use polypropylene?

Mark C [last name deleted for privacy by Editor]
- Malta
2002

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Gavin,

Polyethylene or polypropylene lined stainless steel pipes. If not available, have them built to your specs. Fittings must be sprayed and baked to make them impervious and junctions packed and bolted (no threads). Bye.

Guillermo Marrufo
Monterrey, NL, Mexico
2002

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2002

Temperature is probably the problem. Attack on 316L at 60 F is negligible. At 70 F it is slow, but at 80 F, it is significant.

I would use plastic pipe, PVC or PE or possibly PP. There is a Teflon lined pipe available, but it is expensive. There is a carpenter and a columbium pipe that are quite resistant, but they are also quite expensive, especially when you get into valves and fittings.

Personally, I would run a schedule 80 PVC in a Unistrut trough as the simplest and cheapest possible way, assuming that you stay below 115 F.

James Watts
- Navarre, Florida

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2002

Gavin,

My first response was 'going by memory' ... but seeing that you have been given different suggestions, I will now go as to 'Hoyle' and dig out corrosion charts.

Further, your statement is somewhat nebulous, to say the least. You talk about 98% sulfuric and then say 'flushed out with water'. However,in all fairness to you I have encountered chief chemists who did not have a full handle on their chemistry in their plant which is why I played safe.

For 98% sulfuric the Trovidur type NL PVC is OK to 60 deg. C and their (less expensive) type EN is OK to 40 C. HOWEVER, Polypropylene and Polyethylene are most definitely, emphatically NOT recommended at those concentrations. Ditto for high impact PVC (i.e., sewer pipe), ABS, Fiberglas, etc.

Polyethylene seems to have a slight edge over PP at 90% concentration. Both are OK at 80% but at room temperature. However, you could well encounter stress cracking if the temperature increases even if welded by experts.

I'd opt for ordinary, off-the-shelf Sch. 80 PVC just as James Watt suggested. For the cemented joints, presuming high sulfuric concentrations, you MUST backweld (a day or so later!) Then you can count upon it lasting till you retire!

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

Freeman,

Will try to make it slightly clearer, the acid pumped is 98% then disconnected from the pump cycle allowing sulfuric acid residue to drip in the open air and be washed down a drain with cold water.

Thanks for your ideas am following up on them.

Gavin P [last name deleted for privacy by Editor]
- Mt Isa, Queensland, Australia
2002

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Some more theory. When a school boy engineer evaluates the corrosion properties of a metal in a corrosive he does it by first weighing a panel, then placing the panel in a pyrex beaker [beakers on eBay or Amazon] for a period of time, then removing the panel and weighing it and calculating the weight loss. Then he inserts into a table of corrosion properties his interpretation of the tests.

In the real world when you cut threads in a piece of stainless steel or when you merely bend it, then you have created a galvanic cell and introduced galvanic corrosion.

Theoretically stainless steel stands up against sulfuric acid, however in the real world all sorts of galvanic voltages arise and corrode away the stainless.

As the masters said above - use plastic !

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2002

In this case the conc. is falling due to humidity/water. Actually CSRL (Carbon Steel Rubber Line) will be the cheapest and best for the application.

Gor K [last name deleted for privacy by Editor]
- Moura, QLD
2002

Why flush with water. At low velocity (<1m/s) 98% should be OK on stainless. It will build a stable layer which is not eroded at these low velocities.

However, if you flush with water, you will in effect dilute the existing acid down to strengths which will renew attack on the steel. Do you have to flush/leave it open to atmosphere?

I am only recently looking at a similar problem.

Frank h [last name deleted for privacy by Editor]
- England, UK
2003

As far as I know, pipeline for 98% sulfuric acid are made of carbon steel. In such concentrations sulfuric acid is a reductive one, that's why SS must not be used.

Pascal G [last name deleted for privacy by Editor]
- France
2004

Kindly we need to know the supplier of NL PVC. Please give me the address of supplier because our customer need NL PVC Piping for H2SO4 98%.

Thanks and regards,

Adisorn S [last name deleted for privacy by Editor]
- Bangkok, Thailand
2004

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2006

I have to pass through a small pipe (80 cm) sulfuric acid with maximum concentration 8 % at 70 °C temperature and pressure of 10 bars.
Is 316 SS ok for that ?
If not, any other suggestion ?

Thanks,

Mike S [last name deleted for privacy by Editor]
Engineering - Athens, Greece

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I require the same information as the previous question, will 316 stainless hold up to 8% sulfuric acid wash at 70 - 75 degrees in a 80 mm pipe.

David McDonald
- Phosphate Hill, Queensland, Australia
2007

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2007

Similar to inquiries of Mike S and David M, I'm interested in the temperature dependence of corrosion rate of 316 stainless in 15% sulfuric. Presumably corrosion accelerates rapidly as temperatures rise towards boiling. I'm interested in corrosion rates in the range 90-100 °C (well below boiling for 15% sulfuric but still pretty warm!). This temperature creates some issues for many of the usual "plastic" solutions; plus I have a readily accessible low-cost solution for a suitable vessel in 316. The vessel "only" needs to last 3-6 months. Hence the motivation to explore corrosion rates.

I assume that in fact the corrosion rates will be excessive even for this relatively short life, but thought it worth briefly exploring the possibility ... before I embark on a detailed costing of purpose-built GFRP vessel using special heat- and acid-resistant resins.

Jeff G [last name deleted for privacy by Editor]
- Brisbane, Qld, Australia

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April 2, 2008

I have worked in H2SO4 plant for 2 yrs.

conventional sulfuric acid plant producing 98% acid use cast iron pipe to handle hot temperature ~90 °C. For critical service such as acid cooler or "needs of flushing with water", hastelloy C is used.

US have invention of better alloy known as ZeCor, I never use it and I belief import cost to Asia is high, please consult www.mecsglobal.com for this ZeCor, they design H2SO4 equipments.

for cold 98% H2SO4 small quantity user, use carbon steel and PVC/HDPE/PP is acceptable.
in 98% H2SO4 plant, carbon steel only use for storage tank. carbon steel upon contact with 98% H2SO4, will precipitate passive sulphate sludge that block further acid corrosion. DO NOT scoop out this layer unless it became too thick.

for dilute acid up to 70% H2SO4 <50 °C, use PVC/HDPE/PP lining.
PVC generally do not takes hot acid (>50 °C), this is first time I heard of NL PVC that resist hot acid.

in general never try flush water to acid, high heat and carcinogenic acid mist will form (didn't your chemist teacher told you never pour water into acid, and always perform add acid into water?)
Just drain the acid then use N2 purge.

also never belief SS316 okay for diluted 30-70% H2SO4, it will fail with acid immediately turns to green.
in the past people use lead pipe for this, but now seldom people using it because of lead carcinogenic problem

Ng Yean Min
- Kuantan, Malaysia

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February 11, 2009

Dilute sulfuric acid at temperature? I have corrosion in a vaporiser (115-120 C) containing mostly organic medium, < 0.5% water under high vacuum and therefore high velocities.
Is there any linings/coating that can be utilised under these conditions?
John

John Smith
R&D - Sasolburg, South Africa

According to my experience neither PVC, PE or PP will last. Even PVDF will fail since SO3 will be present in 98% H2SO4 environment. My suggestion is a plastic material called ECTFE (ethylene chloro trifluoroethylene). It's not cheap, but it lasts long even elevated temperatures + pressure; it's even weldable by heating element butt welding.

Peter Gruber
- Austria
December 2, 2009

I'm working in a sulfuric acid plant. I need a pump to circulate dilute sulfuric acid (5-8%)at 80° C. Currently, I'm using rubber lined Carbon steel but having a lot of problems. What material should I use for this pump?

Nitin Jain
Refinery - Jamnagar, Gujarat, India
October 29, 2010

what is the best material for handling of 70-98% sulfuric acid used for chlorine drying in chlor-alkali plants?

Amir Davary
chlorine producer - Esfahan, Iran
May 7, 2011