What inspection checks should be carried out prior to and during
hydrotesting of a heat exchanger?
Following checks are to be carried out prior to hydrotesting of a heat
exchanger.
a) Check whether internal and external touchup has been cleared.
b) Check whether machining of the gasket face has been okayed by the
machine shop.
c) In case of any heat treatment, check that the same is carried out
and recording on chart is OK.
d) After heat treatment if any all remipad pads are tested and found
satisfactory.
e) Check whether expansion/welding of tubes to tubesheet has been
carried out and whether DP of tube-to-tube plate welds is cleared.
f) Check for hydrotest pressure as per latest revision drawing.
g) Check if some special requirements have been mentioned in drawing
or specification.
h) Check drawing for type of gaskets and specifications of fasteners,
especially height of nuts required.
i) In case of jacketed or multi-chambered vessels or in any
configuration where pressurizing one part or chamber is going to exert
external pressure on any other part or chamber, check whether the same
has been designed for taking external pressure. If not then special
testing procedure including precautions etc. should be asked for.
j) During hydro test ensure that work order no., stroke no., equipment
no. is clearly punched.
k) Overflow to avoid anlock is checked.
l) All joints are wirebrushed.
m) Check right fasteners have been used.
n) Check the pressure after pressurizing and mark the position of the
needle of the gauge.
o) Make a list of all the seams, bolted joints and examine them
carefully after pressurizing for any leaks.
p) After complete examination, check the gauge and the marking, for
any drop in pressure. After holding the pressure for the specified
time, the pressure should be released through the top fitting. The
fitting should be removed and the opening should be examined to ensure
that there is no air entrapment, and that the equipment is full of water.
q) Check and record shell circumference before, during and after hydro
to detect any permanent set. Check drawing/code specification for any
X-ray/DP/MP/
r) Special requirements for tube side testing of heat exchangers.
1) Before seeing tube side hydro testing, ensure that the shell side
has been drained and that at least one nozzle preferably adjacent to
the tubesheet on the shell side is open and at the bottom most point.
Any dripping of water through this nozzle should be checked.
2) In case tube side design pressure is higher than shell side design
pressure.i) In `U' tube or floating tube plate type exchangers, i.e.
in cases where the tube bundle can be removed from the shell,
hydrotest should be done with tube bundle outside the shell. The
second alternative mentioned in
(i) below can be adopted if acceptable to outside inspector. This
matter should be discussed with inspection engineer in charge prior to
doing hydrotest.
(ii) In fixed tube sheet exchangers and in other type whose tube
bundle cannot be removed from the shell a bubbling test described in
the following paragraph should be carried out after tube side hydro
test.Bubbling test: Shell side should be completely filled with water
with nozzle adjacent to the tubesheet open and at the top most point.
Tube side should be pressurized with air/N2 at a pressure equal to
design pressure.The water in the shell side nozzles should be observed
for bubbles due to leakage in the tube to tubesheet joints.
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