Working with stainless steel in 3 M HCl solution
The austenitic, chromium-nickel based stainless steel SAE 316 approximately corresponds to the material number 1.4401 or 1.4436. Especially due to the addition of molybdenum in its composition it is more resistant to corrosion overall than the usual type 304 (1.4301). However, it is generally not intended to be used in hydrochloric acid.

Hydrochloric acid lacks the oxidizing properties that are needed to maintain the passive corrosion-resistant surface layer on stainless steel.

The typical corrosion rate in $1\ \%$ hydrochloric acid at room temperature is about $0.1\ \mathrm{mm\ a^{-1}}$, which is approximately $0.1\ \mathrm{g\ m^{-2}\ h^{-1}}$. At higher concentrations or higher temperature, the corrosion rate is strongly increased. Note that your concentration of $c=3\ \mathrm{mol\ l^{-1}}$ $\ce{HCl}$ corresponds to about $10\ \%$ hydrochloric acid.

In addition to this uniform corrosion, stainless steels in media containing chloride ions are particularly susceptible to pitting corrosion, i.e. highly localised corrosion with discrete pits.

Furthermore, stainless steel SAE 316 is prone to chloride-induced stress corrosion cracking at elevated temperatures (over about $50\ \mathrm{^\circ C}$).