Ideal temperature and concentration of hydrochloric acid for pickling super high tensile steel before galvanizing?

A. Sir:

HCl pickle in general, job-shop galvanizing is normally operated at 80 °F (27 °C). Higher temperatures pickle faster, but produce more fumes. A suitable inhibitor protects the base steel and greatly reduces fumes. Few inhibitors in the market-place are suitable. Some cause cancer.

Usual HCl concentration is about 17% down to 5% HCl by weight. Commercial conc. HCl is about 37%, so the conc. HCl is normally diluted one to one with water. If the "straight" conc. HCl is used directly for pickle, then terrific fumes are produced causing the destruction of the plant and surrounding area and the lungs of the workers. Pickling times of 15 minutes to 45 minutes are common.

Higher iron (+2) in the pickle speeds pickling, whereas higher zinc (+2) from stripping (re-work or racking fixtures) slows pickling.

Hydrogen embrittlement in pickling in HDG is rare because the heat of the molten zinc drives out the hydrogen. Of much greater importance is the chemistry of the steel and the chemistry of the molten zinc. Tin in particular must be kept low in the molten zinc because it causes cracking of the steel.

Regards,

A. Hi D R. Please review what Dr. Cook has said about the question and, if his answer isn't quite clear to you, try to phrase your question in terms of what he has already said: But he said higher temperatures pickle faster ...

Regards,

Okay, thanks.