Ultrasound Detection - Testing Tube and Shell Condensers
by Chuck Petersen,
Petersen Predictive
Maintenance
In order to Test these
condensers with Ultrasound we must first understand how they
work. These condensers come in all sizes and shapes. But usually
the principle is the same. The product is run through the shell
side and the water is run through the tube side. Thus the water
flowing through the tubes carries the heat away allowing the
boiling product to condense back into a liquid, or in some cases
just cool down to a desired temperature.
In
this picture the water enters the condenser through the large
pipe on the end. (Green Circle) It then travels through the
tubes and out the other end. This condenser was approximately 40
feet long.
The product enters the
condenser through the pipe that we see in the center of the
picture. (Yellow Circle) Between these two entry points there is
a thick plate that is called a tube sheet.
The water and the
product never actually contact each other but the heat is drawn
away by the flow of water through the tubes that are running
through the product.
This large plate over
the end of the condenser is called the head plate. There is one
on each end. We will need to pull these head plates so we can
get to the tube sheet. That is where we will find any leak that
there might be in this condenser.
Here we see a crew
pulling the head off of one end of the
condenser. These heads are very heavy and should be moved with a
crane or some other device designed for lifting.
The tube sheet is the
barrier between the water and the product. It is positioned
between the product and water entry and exit points on each end
of the condenser. It also holds the ends of all the tubes.
After the head has been
removed and the water box has been tested for safe entry
(Confined Space) then we will proceed to enter for testing. This
is the tube sheet.
Here
we can see the ends of the tubes that run the full length of
this condenser. This is also called the water box. The water
comes in here and runs through the tubes and out the other end
taking the heat with it. If one of these tubes springs a leak
then the product because of the higher pressure is leaked into
the water. In this case it was propane, so the vapor cloud above
the cooling tower was not all steam; it was partially leaking
propane being carried to the tower by the water.
This is where we check
for leaks. These tubes are about ½ inch in diameter. There are
approximately 2200 of them. To test each one individually from
both ends would take for ever. In this case we leave the shell
side charged or we de-pressure it and then re-pressure it with
Nitrogen. That way with the shell side at a higher pressure we
can here the leaking tube. These higher pressure usually only
needs to be approximately 25 to 30 psi.
After the water box has
been cleared by operations and all safety measures are in place
we actually get into the water box and listen for the leak with
the UE SYSTEMS ULTRAPROBE 10000.
Once inside the water
box and using the gross to fine method we
can determine where the leak is. At 25 to 30 psi differential it
is very easy to find these leaks. After we have located the
general area of the leak then I take a cheap plastic funnel and
place end of the funnel inside the tube. I then use the rubber
focusing module check inside the funnel and hear the leak. I
then check outside and all around the funnel. If I hear no leaks
outside and knowing that Ultrasound will not penetrate a solid
this indicates to me that I have located the exact tube that is
leaking.
This tube is usually
plugged and then we go to the other end and plug the other end
as well. This takes that tube completely out of operation and
the unit can be reassemble and put back on line. I have found
condensers with one tube leaking and I have found them with
several tubes that leak, be sure to check them all closely.
This entire operation
took approximately 4 hours from start to finish.