ABB SCK - Page 140

140 Operating instruction SCK Gas Sampling System OI/SCK-EN Rev. E
If the gas sampling probe was installed in accordance with the recommenda-
tions in the Installation section and in the project planning documents, ade-
quate protection of the probe is guaranteed in operation.
The probe (probe pipe and filter) may nevertheless get damaged, above all in
the following situations:
 if material falls on the probe
 of too much material adheres to the probe pipe
 if tire parts or bullets hit the probe pipe
 if red-hot material flows over the probe
 if aggressive combustion residues corrode the probe pipe and filter mate-
rial
 if the probe pipe material is worn by high flue gas speeds (particularly
critical at flue gas speeds > 20 m/s)
The manufacturer offers no warranty for such damage.
The following problems may occur when measuring SO
2
:
 if the gas sampling hole on the tip of the probe clogs up with combustion
particles, an increasing amount of SO
2
is absorbed,
 if a layer of rust particles builds up on the filter unit, SO
2
will also be ab-
sorbed as the sample gas travels to the analyzer,
 if the sample gas condenses in the sample gas tube, part of the SO
2
dis-
solves in the condensation, which in turn decreases the SO
2
concentration
measured in the analyzer,
In the above-mentioned cases, the falsification of results will be all the more
severe, the lower the concentration of SO
2
.
Maximum reliability of SO
2
measurement is given,
 when the gas sampling hole(s) on the probe tips are completely open (i.e.
not clogged up with rust particles),
 immediately after blow-back.
Due to the propensity of rust particles to form incrustations on or inside the
gas sampling system that may result in absorption of SO
2
, the manufacturer
offers no warranty on such measurements.
If it can be assumed that safe operation is no longer possible, the sampling
system must be taken out of operation and secured against being started up
again.
It can be assumed that safe operation is no longer possible:
 if the sampling system is visibly seriously damaged,
 if the sampling system is no longer operational,
 after prolonged storage under adverse conditions,
 after severe transport stress.
Damage
SO
2
measurement
Safe operation no
longer possible