Summary for stainless steel pickling Discussion
Pickling of stainless steels like SS304, 316, and 310 is discussed as a process that should follow established guidance rather than a single universal recipe. Hemant B. Kamat asked what solution to prepare for investment-cast 310, 304, and 316 stainless so the surface would show a pleasing color. Lee Kremer advised checking ASTM A380 for pickling practices and ASTM A967 if passivation is needed to maximize corrosion resistance by enriching the chromium at the surface. Umashankar Gupta added that several acid combinations are used in practice, including triple-acid and double-acid methods such as HCl+HF+HNO3, HCl+HNO3, or HF+HNO3. A later question from Bruno Pinto about stain marks after pickling and passivation of 304L was answered with two likely causes: etching from over- or underexposure to the pickling/passivation treatments, or true water marks from hard-water rinsing.
2002
Gentlemen,
Can you advise me on what solution to be prepared for pickling of stainless steel Gr.310, 304 and 316. These grades are investment cast by us. The pickling should bring out the pleasing colour of stainless steels.
Thanking you in advance,
Hemant B. Kamat
– Belgaum, Karnataka State, India
A. Hemant:
You should look at ASTM A380
for recommended practices for pickling. If you need to passivate to prevent corrosion, you need to see ASTM A967. These grades are quite corrosion resistant, but need to be passivated to obtain the highest chromium content on the surface for optimum resistance.
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
2002
A. There are so many different method for pickling of stainless steel.
Triple acid, double acid are use to pickle above grade. You can use HCl+HF+HNO3 acid or HCl+HNO3 or HF+HNO3 acid.
Umashankar Gupta
– Nagpur, India
December 10, 2008
Staining during pickling and passivation of 304L
Q. Good day to all, I am in desperate need of some assistance. We are currently building 304L stainless steel primary settling tanks & bridges. We have noticed that after we pickle and finally passivate there are stain marks that resemble water marks. What are these due to and can they be removed?
Bruno Pinto
Quality Manager – South Africa
February 9, 2017
A. Bruno,
Two possibilities I can think of:
Etching due to over- or underexposure from your pickling and/or nitric acid passivation treatments.
Actual water marks due to rinsing with hard water.
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
February 20, 2017