Frequently Asked Questions
Under normal conditions, electrodes can last anywhere from several months to several
years depending on the type of operation, rate of production, strength of product,
and quality of the raw materials used in the process. Because each application is
different, there is no average life expectancy. Indication that the electrodes may
need to be replaced are:
- leaking at the electrode
- erratic ORP control
- a significant change in set point to achieve the same excess alkalinity level
- more than 20mv difference in reading between two different sets of electrodes
Sometimes the electrodes will only need cleaning and not replacement.
Contact Powell's Field Engineering and Service department and request Powell Technical Bulletin 101 for more information.
On a continuous system,
some fluctuating above and below the set point is normal and should not be a concern
unless it is tripping the high and low ORP alarms or the desired excess alkalinity
level cannot be maintained. There are so many factors that can cause ORP fluctuation.
A Technical Service Representative can help troubleshoot the problem.
Here are a few of the most common causes:
- worn or dirty electrodes
- partially plugged chlorine line and pressure variations
- unsteady water or caustic flow
- partially plugged reactor
- vapor chlorine or air coming in with the liquid chlorine
- faulty control valve transducer
- a defective control valve
- sticky spool valve positioner
Recommended maintenance procedures and intervals are different depending on the
type of Powell product you own. Consult your Powell operating manual for recommended
maintenance procedures specific to your Powell system. If your operating manual
is not accessible or if you require further assistance,
contact Powell's Field Engineering and Service department.
Powell has a clean, modern repair facility and can repair and calibrate most of
the parts associated with our equipment, such as:
- pressure transmitters
- temperature transmitters
- signal transmitters
- pressure transducers
- pressure gauges
- pressure switches
- flow meters
- air motors
- and more.
Call us at 989.681.2158 or email us
for a return material authorization number (RMA) today.
Powell ORP electrodes can be rebuilt over and over again with the exception of when
the plastic body is broken or the threads are damaged. Electrode repair kits are
available from Powell or you may opt to have a Powell Service Technician rebuild
your electrodes for a small fee. Contact Powell's Field Engineering and Service department
by emailing email@example.com
or by calling 989.681.2158.
The following are the most common reasons not enough chlorine will come into the bleach
- partially plugged chlorine line
- hand or automatic valve somewhere in the pipeline is either closed or not fully
- a stuck check valve
- a defective control valve
- low line pressure or a seated excess flow valve on the rail car
- faulty dip tube in the rail car
The most common cause for dark colored bleach is due to a high iron content in either
the process water or concentrated caustic supply. Occasionally, iron contamination
can also be caused from either an incorrect piping component or a failed liner of
a plastic lined metal piping system for bleach. If you are experiencing a problem,
iron content tests should be done on the water and caustic. A total iron content
in the finished bleach of around 1 PPM or above may start discoloration of the bleach.
A common misconception is that iron will decompose the bleach. Iron will not cause
decomposition, only discoloration. Decomposition is caused by heavy metal contamination
such as nickel or copper. For more information on decomposition, see
Sodium Hypochlorite General Information for the Consumer. A Powell
filter system can remove virtually all discoloration and heavy metals,
making it more stable and giving it a much cleaner appearance. See
Effectiveness of Filtering Liquid Bleach for more information.
Occasionally, the ORP set point will need to be changed due to worn or dirty electrodes.
Necessary adjustments can be determined by performing regular bleach tests. Other
things that may cause a necessary change in the ORP set point include:
- soft versus hard water
- different grade of caustic
- different caustic supplier
- additives in the water or caustic
- air or vapor in the liquid chlorine supply
Powell can help upgrade most bleach systems to run faster than originally designed.
Powell can engineer an upgrade of the current system and offer a complete upgrade
package. Many times most or all of the work can be performed by regular plant maintenance
personnel, reducing labor charges by Powell. Since each installation is different,
consult Powell for discussion of what your system would need.
The most common reason that chlorine valves and hoses on a chlorine unloading system
do not last long is moisture. The moisture could be from padding the car with wet
air or from not capping the hoses and pipelines after disconnecting. This will attract
moisture from the ambient air, attacking the piping components.
Calibration intervals for chlorine detection equipment varies according to plant
procedures and manufacturer recommendations. As a general rule, calibrate all equipment
at least every six months. Since most warning systems and automated shutoff systems
rely on the chlorine detection equipment, it is imperative that it be kept in good
working order and tested at least monthly. Powell offers a chlorine generator that
can be used in calibrating and testing your chlorine equipment. Reference
Troubleshooting Tools for more information.
tanks are recommended at each location where liquid chlorine can be trapped
between two valves, even if the valves are normally left open. One area that is
often overlooked is protection of the flexible transfer lines at the railcar. As
the temperature of the trapped liquid chlorine increases in the pipeline, the pressure
also increases. The expansion tank is designed with a rupture disc to blow at approximately
300 PSI to allow the expanding chlorine someplace to go (and to relieve the line
pressure) instead of blowing a gasket or something else in the pipeline and releasing
chlorine to the atmosphere. Pressure on the expansion tank gauge indicates a blown
rupture disc. When this occurs, the rupture disc needs to be replaced as soon as
downtime allows. The expansion tank should be sized for approximately 20% of the
volume of the area being protected. For more information on sizing see
Chlorine Expansion Tanks