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Pickling of pipes (hydraulic pipe line)

Q. I would wish to have the detailed procedure for Pickling and Passivation of Carbon steel Pipe lines. The pipe that are pickled and passivated will be used in in a oil circulating unit

Sampathkumar Iyengar
Iyengar Engineers - Bangalore, Karnataka, India

Q. We are looking forward to pickle a glycol tower with 7 trays. Please can I have the procedures for pickling and passivation.

Abiodun Akinola
- Warri, Delta State, Nigeria

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I'm an operations engineer at a fertilizer company in Pakistan and these days I am involved in the pickling and passivation of carbon steel pipelines (will be used for steam service) ... till now we have performed degreasing of the pipelines, I would like to share the procedure which is as follows
1.Air blowing for removing foreign particles.
2.Flushing with potable water + leak test.
3.Degreasing with Sodium Metasilicate + Tri Sodium Phosphate + Soap
4.Rinsing with demineralized water.
5.Pickling with 3% Citric Acid + ABF + Rodine 31A
7.Passivation with Citric acid + Sodium Nitrite + sodium carbonate / washing soda [affil link]
8.Final rinsing with slightly alkaline demineralized. water

Hope you find it helpful
Good Luck Mate!

Salman S. Ramay
- Sadiqabad, Pakistan
July 15, 2009

To minimize searching & thrashing, multiple threads were merged; please forgive repetition, chronology errors, or disrespect of other responses (they probably weren't there) :-)

Q. Sir,

We need to pickle pipes for hydraulic line as tine particles of rust or oxide may damage our costly pump. We have a pipe which is 18 meters long and 12" in diameter and process we adopt is as follows.

First we pass the soda to remove oil etc, then water, then acid, then water, then nitrogen and at last we apply hydraulic. Even after doing that pipe is becoming rusty. There is time difference of 15-20 between each pass as we have to change the setup.

For small pipes we are simply dipping them in acid tank and then in water tank and then applying hydraulic oil. Neither cleaning is perfect nor further rusting is prevented. Some one have suggested applying rust preventing oil after pickling. I need to know if RP oil is safe to use in hydraulic line. Somebody please answer my all 3 queries.


Atul Mishra
MS pipes manufacturing - Anjar, Gujrat, India

A. Guardian Anti-Corrosives in Chennai, India, has proper de-rusting chemicals which will leave the pipes in a relatively passivated condition.

Consider using a less hygroscopic hydraulic oil containing corrosion preventatives. Don't risk compatibility problems with D-I-Y additions; contact the oil manufacturer's rep.

Ken Vlach [deceased]
- Goleta, California

contributor of the year Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

A. You need to tell us your exact process, from the information you have given no-one could make any reasonable suggestion.
What is the material of the hydraulic pipes? It may be simply that a change of material will solve your problem.
What is the exact formulation of the pickle you are using, how long are you leaving it in contact with the steel? If your process is not robust then you may be leaving the material open to corrosion.
Finally I would not even consider a rust preventative oil as this will contaminate your hydraulic oil. You should consider a hydraulic oil with corrosion inhibitors as part of the make-up of the oil.

Brian Terry
Aerospace - Yeovil, Somerset, UK

A. Atul,

Try adding Sodium Nitrite (0.5%) in your final rinse. This will passivate the metal and prevent flash rusting. You can increase the concentration if necessary but I would not go over 1.0%. Also, use demineralized water for rinsing as the chlorides in city water will only contribute to corrosion. Hope that helps.

Joseph Lockrem
- Indianapolis, Indiana

Q. Dear Sir,

thank you for your response.

Dear Mr. Joseph, please let me know the specification of Sodium Nitrite to be used, i.e., concentration, grade etc.

Dear Mr. Brian, here is the detail of process we are adopting-
1. degreasing by 5% soda for 1 hour.
2. rinsing by soft water for 15-20 min.
3. de-rusting by HCl acid for 20-30 min, 18-20% concentrate.
4. rinsing by soft water for 20-30 min, pH after rinsing 5-7
5. Again soda flushing 20-30 min followed by water rinsing.
6. hydraulic oil flushing for making a layer of oil.

There is delay of approx. 15 minutes between each step for change-over. I hope I provided all the detail. Please analyse and advise.


Atul Mishra [returning]
- Anjar, Gujrat, India

A. Atul,

Can you tell us what the material is that the pipes are made of? You do not actually passivate the steel with any of the steps described (assuming that you are using a corrosion resisting steel).
Adding a corrosion inhibitor to the hydraulic oil will help. You need to talk to your hydraulic oil supplier for help with this.

Brian Terry
Aerospace - Yeovil, Somerset, UK


Q. Sir,

Pipe is made of MS (Hot Rolled). You are correct, we do not have a stage where passivation takes place.


Atul Mishra [returning]
ERW Pipes Manufacturing - Anjar, Gujrat, India

A. Atul,

Your problem has little if anything to do with your hydraulic oil. I assume the pipe is carbon steel and I assume it is installed. If you are going to run the pickling process again, I recommend the following. Degrease with 2-5% sodium hydroxide for 60 minutes at 140 °F (or best attainable temp.), then rinse with hot soft water until effluent pH measures 7.0 or less. Then configure the system for recirculation and add enough citric acid to achieve a 10% (w/w) solution and circulate at 120-140 °F for 60 minutes. Rinse (once through, do not recirculate) with hot soft water and 1% sodium nitrite for 30 minutes. Drain the pipe and blow dry with either nitrogen or clean dry air (-40 °F dew point) until the effluent pressure dew point measures -20 °F or lower. I would install an inlet valve manifold that will allow you to switch between chemicals with no delay. It is difficult to address all the issues you may encounter when you undertake this process but that is the basic outline. You will need a very large pump to achieve the velocities necessary. I would call a firm near you that specialized in this type of work and they shouldn't have any trouble turning over a clean dry pipe to you without any hydraulic oil being used. Purge with nitrogen and cap if you aren't going to put it into service right away. Good luck.

Joseph Lockrem
- Indianapolis, Indiana

A. 1. Clean with 5% TSP, wetting agent and water solution, rinse, dry and inspect for cleanliness.
2. Pickle with hot 12-15% Sulfuric/water solution with an added inhibitor such as Rodine 31A. - 140-160 degrees
3. Rinse with hot water (Over 140 degrees)
4. Neutralize in 2-3% soda ash solution 140-150 degrees
5. Rinse with hot water (Over 140 degrees)
6. Passivate in a hot solution made with .25% Sodium Phosphate Monobasic, .25% sodium Phosphate Dibasic and .5% Sodium Nitrite and water (150-160 degrees)
7. Dry with hot air (Don't rinse after this step) and inspect
8. Coat with a rust inhibiting oil.

Bart Snow
- Ponte Vedra Beach, Florida
December 29, 2010

Q. Hi,
I am Deepak, Mechanical Engineer,

How long can an HCl pickled & oiled material remain without rust. Or what is the life of pickled material (avoiding rust)?

Deepak Parishwad
tube mfg - Pune, Maharashtra, India
August 17, 2012

In-situ pickling of underground pipe

Q. Dear sir
Please send me the exact process with chemicals name for pickling of underground 120 meter length and diameter 63 mm, ms pipe line, please send me step by step process and how to neutralise used chemicals.

Anil Jain
- Surat, Gujrat, India
October 16, 2013

A. Hi Anil. There's no harm in asking, but realistically nobody is going to write that book chapter for you and post it here. Furthermore, it's dangerous to attempt such operations without prior hands-on training. Please retain a company offering on-site pickling and passivation services (there are a lot of them).


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Q. Sir,

We need to pickle pipes for hydraulic line of carbon steel as fine particles of rust or oxide may damage our costly pump. We have a pipe which is 270 meters long and 1.5" in diameter. Please give me the process how can I pickle the pipe.

Sukesh jha
enterprise - Jamshedpur, jharkhand, India
August 11, 2015

A. Hi Sukesh. Anil received no answers in 2 years now, so I don't think your inquiry will either. Please retain a company offering on-site pickling and passivation services. Maybe you can work with them and learn how to do it yourself next time ... maybe. But it's hard to go from apprentice to master in a day.

As someone with many decades of general metal finishing experience but no experience with in-situ pickling & passivating of pipe, I wouldn't even dream of attempting it myself :-(


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Sukesh,
We need to clarify a couple of things. Are these pipes carbon steel or stainless steel?

If it's carbon steel, you can "pickle" it with a citric acid solution, which ought to strip off some material and give you a fresh surface. Since the pipe will still be carbon steel, though, it doesn't really sound like a permanent solution -- you may want to insert a filter in-line ahead of the pump instead.

If it's stainless steel, you're not really after pickling. Pickling is to improve the appearance by removing scale, etc. You want to passivate, the removal of surface iron to promote corrosion resistance. This can also be done with citric acid. Though again, if you have had a problem with your pipe developing rust particles, you are presumably subjecting it to fairly corrosive conditions and you may want to insert that filter to guard against future rust particles that may develop.

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Ray Kremer
Stellar Solutions, Inc.
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McHenry, Illinois
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