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Technical Bulletin
Identification:
Bulletin no:
Date:
Issuer:
Factory:
GENERAL
PDX2000-09
19-09-2000
R.ZAGO (T.T.&S.)
Vallenoncello Cooking
POSTAL ADDRESS TELEPHONE TELEFAX
ELECTROLUX FSE Electrolux ZGI V.le Treviso 15 +39 0434 380570 +39 0434 380555
33170 PORDENONE - ITALIA
Page 1
FOOD SERVICE EQUIPMENT
English language
THE WATER AND THE APPLIANCES FOR
PROFESSIONAL COOKING
THE WATER AND THE APPLIANCES FOR PROFESSIONAL
COOKING
WHAT YOU NEED TO KNOW BEFORE SELLING AND INSTALLING AN APPLIANCE
Object
The lack of information, and the fact that there is not such a thing as a “culture of the water” among
those professionals who operate in the catering sector, is most times the source of many technical
problems which then cause the fast degradation of performance and reliability of the appliances used
for cooking foodstuff. The object of this technical bulletin is that of supplying our retailers and
engineers who carry out the installation and servicing of machines and appliances with the necessary
and sufficient elements that will allow them to evaluate first and to operate then so to avoid any
damages the water might provoke (corrosion and scaling) on the materials used for manufacturing the
machines and to choose the best water treatment possible.
Application field
Combined ovens with and without steam generators, indirect pans and all other functions of usual
modular catering .
The water, general news …
The water in the world is ever the same, it gets continually recycled in a perfect closed system. The
water in the seas, rivers and lakes evaporates continuously provoking the separation of impurities and
salt which remain in solid state.
Therefore water ascend towards the higher stratus of the atmosphere where it condenses to the solid
state dissolving (loading) the oxygen and the nitrogen and then precipitates on the earth (rain, snow,
hail) dissolving the carbon dioxide that the water contains. When the water enters in contact with the
soil and while flowing through the superficial stratum, the salt contained in the water dissolves. Then
water flows along impervious underground stratum until it gets pumped outside or it finds a natural
outlet. Now it continues flowing, it loads bacteria, it fills with vegetal and animal life until it evaporates
again so starting its natural cycle.
a) The water may contain substances such as:
b) Big suspended particles (sand, organic substances)
c) Average colloids (sulphides, metallic hydratez, detergents)
d) Molecular solutes such as gas, undissociated (sugar and silicates) and dissociated (ions)
molecules.
The main gas dissolved in water are… … Nitrogen (N2), Oxygen (02), Carbon dioxide (CO2),
Ammonia (NH3), Natural gas (CH4), Chlorine (CL2).
And the ions dissolved in water are …. Hydrogen (H+), Potassium (K+), Calcium (Ca++), Magnesium
(Mg++), Iron (Fe++), Copper (Cu++), Chloride (Cl-), Bicarbonate (HCO3-), Carbonate (CO3--),
Sulphate (SO4--), Phosphate (PO4--)
Apart from these elements the water contains also living organisms such as mildew, weeds, bacteria,
virus and chemical compounds deriving from industrial technological treatments.
Water is considered drinkable when suitable for human diet. To be drinkable water must contain every
element within a maximum limit of concentration.
Other substances must be absolutely absent such as: bacteria, virus, mildew, weeds, fungus, lead,
arsenic, chromium, cadmium, barium, cyanide, selenium.
Drinkable water might not be suitable for the correct functioning of a cooking appliance.
3
What is the corrosion…
Corrosion is the electrochemical phenomenon that provokes the progressive deterioration of all metallic
materials that enter in contact with aggressive agents (water, humidity). All professional cooking
machines are made of stainless steel (Aisi 304, 430); these materials are more resistant to corrosion
than other ones thanks to the greater presence of chromium (10,5 that distinguish stainless steel from
other iron alloys. This element is capable or reacting (passivation) when entering in contact with air
containing great quantities of oxygen (oxidant agent) by forming a special oxidized superficial film that
protects the material underneath. When stainless steel is in these conditions it is called “passive” and it
means that the metal is subjected to a very slow thermodynamic corrosion. Otherwise stainless steel is
called “active” when it reacts rapidly to the corrosion process. Naturally the passive film will get
recreated when ripped if the environment is sufficiently oxidant and if the oxygen is able to enter in
contact with the alloy. In short, it means that these materials protect themselves against the corrosion
by means of an “auto-regenerative protective skin” that slows down the electrochemical corrosion
process. According to the state it is in, passive or active, the stainless steel will oppose a valid
resistance to corrosion or will be destroyed by it. Even if the stainless steel resistance to corrosion is
greater that that of other metal it does not mean that, depending on its atomic structure, on special
environmental conditions, on the type of technological process undergone and mainly to the presence
of particular aggressive agents, after a variable incubation period the material protective film might get
ripped. In these conditions the destruction of the material underneath is very fast arriving to break or
even to get perforated. Hence there are not such a thing as a “magical” material but only materials that
can be more or less resistant to corrosion. There are various forms of corrosion, the following ones are
those more common for cooking appliances:
UNIFORM CORROSION
It is most common for fry-top and iron brat-pans. Corrosion forms a oxide film on a wide surface when
in presence of a very aggressive environment (humidity, water), it attacks mainly iron and specially
rough surfaces.
STRESS CORROSION Fig. A
Fig. A
It is very common on cooking appliances and it shows on
cells, steam generators and oven heat exchangers and in the
indirect pans cavity walls. It appears when the material present
in the corrosive environment gets mechanically stressed by
traction or cut in static or dynamic conditions. It takes the
form of branched cracks near the welding at a very high
penetration speed (up to 2 mm/hour) so that when the crack
becomes visible the material is already damaged. Stress
corrosion happens mainly caused for the following connected
facts:
• Stress by external traction due to the use of the appliance
itself or caused by the presence of material internal pressures
due to cool mechanical process (plastic deformation such as
stuffing and bending) or to thermal treatment (welding).
• Presence of an corrosive environment ( Chloride )
• Frequent thermal variations and high temperature.
Stress corrosion is a electrochemical corrosion but accelerated by the mechanical stress.
4
Intercrystalline corrosion Fig. B
Fig. B
It etches chromium stainless steel (Aisi
430-304-316-321), the material crumbles
and gets pulverized grain by grain. The
crystal lattice that unites the molecular
structure of stainless steel brakes due to
the precipitation of the chromium carbide
on the borders of grains at temperature
higher than 500°C. Imagine 2 contiguous
crystals, part of the chromium migrates
towards the border between two grain so
incrasing the concentration of chromium
on the border of every grain which
becomes much higher than the material
average. This way the concentration on
zones (fig. B1) near by the grains borders
gets depleted of chromium until
“uncovering” the zones right by the
borders that this way become vulnerable to
corrosion agents. So both grains separate. The weaker parts are the ones that have undergone thermal
treatments (welding) and mechanical processes (moulding, bending, skirting, etc…) and that operate at
temperatures between 450 and 850° such as heat exchangers).
PITTING - Fig. C
Fig. C
This is the most common one on the
cooking appliances, very much on the
pans wells and brat-pans and easily
recognizable once the process is in
course due to the formation of black
points (from 0.1 to 1 mm) that can
even perforate the whole material
thickness. It shows when the stainless
steel is left in contact with the
contaminant solution (salt or water
having a very high percentage of
chloride) locally and in stagnant way.
The point shaped corrosive attack
operates in two phases, the first one
called “incubation phase” brakes the
passive layer, the second one called
“growing phase” presents a penetrating
or cavernous self-accelerating process
in the sense that feeds itself. From the
electrochemical point of view the
phenomena is caused by the formation
of a kind of battery between the metal
(cathode) and the contaminant (anode);
the electric current between the
cathode and the anode brings in the
solution (dilutes) the metallic ions so
creating the pitting. Chlorine ions CL-
increase on the bottom of the pitting so
speeding the point penetration while
the lack of oxygen on the pitting
bottom prevents any attempt to
regenerate the passive film.
5
GENERAL RULES
Before carrying out any operation on the product or on the installation it is convenient to define
precisely some fundamental concepts that apply to all machines used for cooking foodstuff. Lets listed
here bellow:
• As already described the corrosion is a complex phenomenon that shows itself in various forms
and different causes that provoke the same effect, that is to say the destruction/breaking of the
material. The main cause of any type of corrosion is THE CONCENTRATION OF
CHLORIDE in the water. The greater the concentration of chloride the more aggressive will
become water and consequently the fastest will be the corrosion phenomenon.
• Once the stress or intercrystaline corrosion processes are in course (since the moment it is visible
to the naked eye), the phenomenon can not be stopped but only slowed down. Therefore
prevention it is most important by measuring the quality of water and installing the most suitable
water treating system while installing the appliance. As we intend to demonstrate along, pitting can
be removed if diagnosed in time.
• Temperature helps the corrosion process acceleration; having the same concentration of chloride
and material, corrosion process will be faster on that material which operates at the highest
temperature.
How to prevent corrosion… and scaling …
The measuring phase …
Water is, therefore, the most dangerous element since it might contain contaminants; remember that
drinkable water could be harmful to the appliances and so it does not represent any “security”.
Before installing an appliance you need to control that the tap water is suitable to be used by means of
the 3 parameters that influence aggressiveness against corrosion such as :
1. Concentration of chloride
2. Electrical conductivity
3. PH
A forth parameter is fundamental for the appliances to work correctly: the water total hardness; this
value determines the capacity of a particular type of water to produce scaling.
As already said, the quantity of chloride in solution is the most important characteristic that determines
the initiation and propagation of the corrosive phenomenon. It gets measured in mg/l (milligramilitre)
or ppm (parts per million) by means of a kit (fig. 1-2) which is very easy to find.
Fig. 1 Fig. 2
6
To measure the quantity of chloride in the water carry out the following operations:
1. Take 6 ml of water using the special syringe and inject it in the 2 containers (fig 3)
2. Dissolve 6 drops of reactant Cl-1A in both containers (fig.4)
3. Close one of the containers and place it on the left part of the comparator (fig.5)
4. Dissolve 6 drops of reactant Cl-2A in the other container, close it and shake it, then place it on the
other hole of the comparator (fig.6).
5. Compare the right sample colour with the supplied chromatic scale, when colours are the same
read the ppm value on the bottom right side (fig.8).
Fig. 3 Fig. 4 Fig. 5
Fig. 6 Fig. 7 Fig. 8
The conductivity is the propriety that allows the water to conduct electric power, it gets measured in
microsiemens/cm by means of a conductivitymeter (Fig.9).
Switch on the instrument and plunge it in the water, then read the value displayed by the relative
indicator (fig.10-11).
Fig. 9 Fig. 10 Fig. 11
The PH indicates the acidity or the basicity of water from 1 to 14 in which 7 represent the neutral,
under this value you have a acid solution, over this value you have a basic solution. The more acid the
water the more aggressive. The PH is easy to measure by means of indicative paper strips (fig.11)
which colour change when immerse in the solution you need to measure. Then you compare the colour
of the strip with an special chromatic scale supplied to find out a good approximate value.
Fig. 12 Fig. 13 Fig. 14
7
The total hardness express the capacity the water has to form magnesium and calcium carbonate
(CaCO3) more commonly called scaling, scaling is favoured by the increasing of temperature.
These compounds deposit on the container walls and piping forming the scaling which often breaks the
cooking machine. The total hardness is measured in French degrees or milligramlitre of calcium
carbonate with the following relation: 1°F = 10 mg/l
Sometimes the water hardness is also measured in German degrees (°d) with the following conversion
1°F=0,56 °d. Water is called “soft” when hardness value varies from 0 to 10 °F, low hard water when
hardness varies between 11-20°F and very hard > 40°F.
The hardness values advisable for installing cooking machines are those compressed between 0,5 e 5°F
.
To measure the hardness there is a kit (fig.15) easily find in the shops that has to be used as follows:
1. Take 5 ml of tap water using the syringe and fill it in a test tube (fig.16)
2. Dilute 3 drops of reactant 1 in the test tube and shake it (fig.17), the water becomes red coloured
(fig. 18).
3. Using the special pipette take reactant 2 until filling up the pipette to mark “0” and dilute the
contains of the pipette one drop at the time until water in the test tube becomes green (fig. 19-20-
21)
4. Read the hardness value on the graduated scale; in case you need to add again reactant 2, add the
values read during the second measuring on the graduated scale (fig. 22).
Fig. 15 Fig. 16 Fig. 17
Fig. 18 Fig. 19 Fig. 20
Fig. 21 Fig. 22
The choice of the water treating system …
Once you have measures the 3 parameters related to corrosion and the total hardness regarding the
scaling, control if the tap water needs to be treated and if so try and choose the most suitable system.
First of all control the water aggressiveness and then the water hardness, you will choose the system to
be installed by combining the 12 following results:
1. Choose the reference table according to the appliance you intend to install (C for FCV with steam
generator; B for ISG ; A for indirect pans ) .
8
NOTE: THE TABLES HERE BELLOW ARE TO BE USED AS A REFERENCE FOR AISI 304
APPLIANCES.
2. Multiply the conductivity value for the PH value read and mark the value on the axis of the
abscissa (fig.16).
3. Mark the chloride value read on the ordinate axis (fig.17).
4. Cross unite the 2 resultant values and check in area you are, for example in case of having as
reference table C:
Area 1 = No treatment required
Area 2 = Install a NANOFILTER
Area 3 = Install an OSMOSIS
Example : You have measured the tap water and read these values PH=6.4 ; Conductivity = 850mS/cm;
Chloride = 35 ppm and you need to install and oven and steam generator (as a reference you need to
use table C) the suggested treatment is that of installing a NANOFILTER .
Now according to the value of the total hardness measurement, you need to combine both results to
choose the most suitable treatment using as a reference table D .
Tab. D
1
Not required Not required Nanofilter Nanofilter Osmosis Osmosis
2
< 5°F > 5°F < 5°F >5°F < 5°F > 5°F
3
Not required Softener Nanofilter Nanofilter Osmosis Osmosis
Where …
1= Measuring result of tables A,B,C
2= Total hardness measuring result
3= Treating system to be installed
As you can see, both the nanofiltering and inverse osmosis resolve the problem, so it is convenient to
install a water softener, which is more convenient, only when you have not very aggressive hard water.
While installing one or more appliances pay attention also to these points:
• Make sure there is a 100 micron cross section net filter installed to eliminate suspended solid parts
(sand, metallic residuals, etc…) that could tamper the valves and cocks and are the source of many
bacterial infections. Clean the filter every 2 months more or less.
• Control the water static pressure on the appliance inlet using a pressure gauge; pressure value
must be compressed between 1,5 and 3 bar .
• If you need to install a water softener, control that there is also a sterilization system to prevent
bacterial proliferation.
• If you need to install steam generator ovens and an inverse osmosis device, water conductivity
falls almost to zero. Under these conditions the water level control system of steam generator will
not work, and therefore you will need to reset a certain minimum salinity level in the water. To do
so by-pass a certain quantity of not-treated water to obtain a conductivity in the steam generator
inlet of at least 50 microsiemens/cm.
9
Tab. A
10
Tab. B
11
Tab. C
12
THE ADVISED TREATING SYSTEMS
NANOFILTERS type ZA01 – code 922186
The nanofiltering treatment operates making water in pressure pass through a filtering membrane
which holds suspended substances (salt). The nanofilter reduces the quantity of chloride of 80% (if you
have 35ppm in the inlet, there will remain 7 in the outlet) and “purifies” around the 80% of all
substances contained; on the average you will have 30 litres of “purified” water every 100 litres.
Correct maintenance of prefilter and membrane is most important for the machines best performance
and therefore for the appliance itself. Replace the prefilter twice a year, wash the membrane twice a
year and replace it every two years when water has a hardness value up to 40°F, when hardness
value is superior to this value the filter should replaced at least 3 times a year, for replacing instructions
consult the installation and use instructions manual.
The inverse osmosis treatment is similar to the prefiltering one but for the fact that the reduction of
salinity and salt chloride in the water falls to 99%. The inverse osmosis system is a good prevention
against corrosion but for the cases in which chloride contamination happens after the water have
been treated. In this case water aggressiveness increases exponentially until becoming more dangerous
that if it was not treated. Therefore pay attention when installing inverse osmosis systems in premises
used to salt food in the cells!!.
Passiving liquids are an efficient remedy against pitting only when the phenomenon is in its initial
phase and pitting is not very deep. These liquids (nitric acid) are capable or regenerating the destroyed
protection film; it is, though, absolutely necessary to eliminate first physically all the pitted zones by
removing the damaged metal. This liquids can be used on brat-pans wells, pasta cookers and pans. The
use of these liquids do not represent any advantage when used in case of stress corrosion or
intrecrystaline corrosion. Carry out the following operations:
1. Remove the damaged zones and pitting by smoothing so to create the smoothest possible surface,
wash and dry accurately.
2. Apply a thin film of passiving liquid (passivation creates by itself when entering in contact with
the air).
Demineralizing and deionizing systems are devices that “purify” completely water that becomes
free from any substance different from the base molecule H2O. The use of deonized water
enriched with orthophosphate sodium in 0,1% solution is indicated for indirect pans. Never used
pure deionized water since it is most aggressive on stainless steel. The orthophosphate sodium is a
corrosion inhibitor that increased the passivation of stainless steel which so becomes “tougher”
on corrosion; it is supplied with pan directly in the manufacturer premises. It is not necessary to
add it during the topping up but in case the cavity wall should be completely emptied it will need
to be replaced.
WATER SOFTENER type LT8 code 921305
The function of the water softeners is that of preventing the scaling; these machines change the calcium
(scaling) contained in the water with sodium that do get encrusted. The water softener is composed by
container for special porous resins which contain sodium deriving from the division of cooking salt.
Resins hold the magnesium and calcium carbonate and release sodium carbonate. When the sodium
contained in the resin is finished, the resin needs to be refill with sodium which must also be diffused
by means of a “regenerative” phase. Regeneration phase may be manual or automatic and is carried out
generally by adding common cooking salt in the special container. If resin regeneration is not carried
out regularly, the water upstream and downstream the water softener will be the same, as if were not
treated. It is convenient to install automatic water softeners so be sure that resins will be regenerated
automatically without depending on the operator.
The capacity of a water softener is expressed in litres of resin , the resin lasting time is more or less of
2000 regenerating cycles after which it should be changed; a litre of resin softens a variable quantity of
water according to hardness:
13
Consumption
H2O (Lt/H)
Hardness in °F H2O softened x
litre of resin
H2O softened
with 5,6 litres of
resin (Litres)
Regeneration
frequency (hours)
10 10 215 1200 120
20 10 215 1200 60
30 10 215 1200 40
10 20 200 1100 110
20 20 200 1100 55
30 20 200 1100 37
10 30 180 1000 100
20 30 180 1000 50
30 30 180 1000 33
10 40 160 900 90
20 40 160 900 45
30 40 160 900 30
10 50 140 800 80
20 50 140 800 40
30 50 140 800 26
10 60 125 700 70
20 60 125 700 35
30 60 125 700 23
When installing a water softener you need to install also a “Sterilization” system, that is to say an
electronic device that clean away bacteria and virus in the resins that deposit during the treatment. The
water softener LT8 code 921305 is supplied with its own sterilization system code 921306 .
All type of water softeners and specially ion exchange water softeners are often used incorrectly for
contrasting corrosion. In this point we need to be definitive: water softeners do not modify the water
aggressiveness. Therefore do not absolutely install water softeners if you have corrosion problems
since this systems function is only that of preventing scaling.
Which are the systems you will avoid installing
Electric/electronic and magnetic systems …
This type of systems are very common and there function is that of interacting with water molecules so
that scaling unites in more round forms which are easier to remove. They are absolutely not reliable if
the water temperature is over 60°C .
Chemical additives …
They are very common, there are also many types available; here by we indicated some of them :
• PH correctors
• Filming aliphatic polyamide for protecting piping against rust
• Polyphosphate descaling
All these products are toxic, produce foam that damage the oven’s electronic level regulators and in
any case are not reliable when water temperature is 60°C .
/
