The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Research into over pickling (acid descaling)

Dear sir,
Can you provide the detail of acid pickling process. What the advantages & disavantages of acid descaling. Compare between Hydrochloric acid & Sulfuric acid pickling. What are the details or parameters one should take care to avoid over pickling?
If some of the wire rod has oxide scale pear off, & some portion is rusty, will that cause over pickling onto wire rod. If yes, how to overcome it?

Thank you,

Regards,

Paul Ooi
student - Malaysia
2005

---

What grade/course is this coursework in, Paul? You have asked a lot of questions but they are provided without any context that we greatly help us in trying to help you.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

---

Dear sir:
Can you provide the difference between two acid pickling process for low carbon wire rod? If the surface wire rod is not good( scale peel off, rusty, some mechanical scratches), is that the acid will attack the particular portion? Is yes, what happened on the wire rod after acid pickling? ( pitted ?)
Where can I get the information of acid pickling process? Is that provided at internet?
Thank you.

Regards,

Paul Ooi
- Malaysia
2005

---

2007

If you use unwetted HCl you may get uneven pickling. use a suitable surfactant to get best results. Normally when you have rust, that rusted portion is already a depression due to the metal being oxidised, therefore there already is pitted surface and even with a good wetting agent, you are not going to smoothen out that pitted spots. You are just seeing the pitting clearer when the ruts have been removed.

Clear as mud?

Best regards,

Paul Ooi Kong Hwee
oil and gas presently and previously metal finishing with occidental chemicals for 10 plus years - Kuala Lumpur, Malaysia

---

2007

Hydrochloric acid as compared to using sulfuric acid:

1. HCl works much faster than H2SO4
2. 13% of HCl concentration works just as effectively as using 98% of H2SO4
3. The HCl does not leave any significant attack on the steel but only works on the iron oxide on the surface
4. Less heat was required, saving 35-40% of the steam
5. Less chance of over pickling because HCl only attacks the iron oxide
6. H2SO4 being the main spent acid still requires HCl to remove the fine residuals of iron oxide on the wire itself

Wirdamazni bt Hamid
- Malaysia

What happens to the MS surface when it is overpickled by sulfuric acid? Is some sulphate or oxide formed?

Anindita Chakraborty
- Kolkata, India
December 22, 2011