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Sulphuric Acid corrosion to stainless steel

Current question and answers:

October 15, 2013

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 17, 2013

A. You appear to have done your homework quite well.
If it is thick pipe, you probably would not have a problem.

The one thing that you did not mention from you curves was the affect/effect of temperature. It makes a major difference. At 75 °F and below the attack on 316 is not that bad at 30% by weight. Above that the attack increases significantly.
For your test, can you pack it with an ice bag or even direct an air conditioner flow at it.
You might wrap it with a thin wall stainless tube and flow ice water or cool water through it. You might even use polypropylene tubing.

Finally, it will depend on what else is in the water. Chlorine or chlorides would not help.

James Watts
- Navarre, Florida

Closely related historical posts, oldest first ...


I am trying to find the best corrosion resistant pipeline to use as a drain for 98% sulphuric 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

"Sulfuric Acid Manufacture"
from Abe Books

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Hi Gavin,

Sulphuric 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 sulphuric 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 portrait
Freeman Newton [dec]
(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



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


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

"Sulfuric Acid Use and Handling"
from Abe Books

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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% sulphuric 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% sulphuric 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 sulphuric concentrations, you MUST backweld (a day or so later!) Then you can count upon it lasting till you retire!

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



Will try to make it slightly clearer, the acid pumped is 98% then disconnected from the pump cycle allowing sulphuric 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

"Sulfuric Acid Use and Handling"
from Abe Books

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Your purchases make finishing.com possible


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 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 probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina


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


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


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


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


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 ?


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


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

David McDonald
- Phosphate Hill, Queensland, Australia


Similar to inquiries of Mike S and David M, I'm interested in the temperature dependence of corrosion rate of 316 stainless in 15% sulphuric. 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% sulphuric 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

April 2, 2008

I have worked in H2SO4 plant for 2 yrs.

conventional sulphuric 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

February 11, 2009

Dilute Sulphuric 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 Smith
R&D - Sasolburg, South Africa

December 2, 2009

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

October 29, 2010

I'm working in a sulphuric acid plant. I need a pump to circulate dilute sulphuric 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

May 7, 2011

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

July 18, 2013

A. Oleum (98% H2SO4) below 70 °F can be moved inside Cast Iron pipe. According to Worthington, H2SO4 25% concentrations, and below 100 °F can be made with CF8M castings. High velocity OK.
Worthite is the proprietary product for all ranges of H2SO4, as well as Alloy 20, which is the optimum for castings and wrought, all temperatures, all concentrations. Not cheap but safe.

Jerzy Moszynski
pumps - Parksville BC Canada

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