Hello Vince S,
From the photos, I could not tell for certain if the dripping pipe is from the pressure relief valve. If that's what is dripping:
First, check the system pressure when it's cold. If it is over the relief valve setting (usually 30 PSI-G), the automatic make up water pressure reducing valve needs adjusting, rebuilding or replacing.
If system pressure is OK cold:
Check the pressure of the diaphragm in the expansion tank. That tank has a rubber diaphragm separating the tank into two compartments. One's air and one is water.
If the air section loses its air charge, the pressure relief valve generally will drip when the boiler heats (and sometimes when not heating).
There is a Schrader fitting on the bottom of the tank. Check the pressure with a tire gauge. A rule-of-thumb is 12 psi-g.
You can pump it up with a bicycle pump.
If water comes out when you put the tire gauge on the fitting, the diaphragm is broken in the tank. Then then tank needs to be replaced. Be Careful- It will be very heavy because it is full of water.
(Note: When you have time, the expansion tank really should be supported by framing or a floor stand, instead of the piping.)
Next Problem: If the relief valve has been dripping for a time, it's seal might be compromised by sediment or lime. You may have to change it, too.
I Hope This Helps!
Paul.
If you want to be really accurate when calculating expansion tank pressure requirements:
Pa = H(dc / 144) + 5
Pa = Tank Air Pressure
H = Height in feet from top of tank to highest item in heating system
Dc = Density of the fluid in t he system in cubic feet. (Water at 70-F is about 62.3 pounds per cubic foot)
5 = Typical PSI-G at highest point in system. (You can change this if yours measures differently.)
144 = The constant conversion factor