ENP on Brass Components: No coating build up

Hi

I wanted to add up one info..

The expired chemicals are checked at the supplier's laboratory and okayed for production.

sorry for missing the info..

thanks...

Plating with expired products is always problematic but I think that your problem is that you are plating directly on brass .If you have more than 3 turnovers probably you introduce some lead from the brass, inhibiting your bath.
I recommend to do a copper strike before the electroless

What happens when you plate a steel part?
If it is OK, it means that the electroless solution is OK.

As for plating on brass - brass, unlike steel, is not autocatalytic in EN solution. The best way to ensure good adhesion and coverage is plating a nickel strike layer prior to the EN.

Leaded brass always needs a dip in fluoboric acid (5-15%)

Apparently your bath is contaminated or over stabilized. There are other substances that slow or kill the reaction besides nitrates from the acid leach, like lead, copper, chrome, etc. A dropped part in the tank may have dissolved. The tank walls or racks could have dissolved. Depending on the severity of the problem, you may have to dump the bath and prepare a new fresh bath. In the future, if you intend to keep plating over leaded brass, maybe you should consider a proper pretreatment with fluoboric acid and perhaps a formal initial strike of electro nickel in another tank instead of the electric kick.