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solvents should be avoided.
III RULES FOR USE
III.1 Maintenance
The flexible tubes should always be handled with a minimum of
precautions. For example, they should not be dragged on sharp or
abrasive surfaces, subject to shocks, cutting, deformation, or run over by
vehicles.
Suitable transport should be provided for the heavy flexible tubes supplied
in straight lengths, especially when lifted.
III.2 Sealing Test
After the metal fittings have been assembled, a hydraulic test under
pressure is recommended to ensure that they are in satisfactory condition
(no leaks or slippage of the fittings with the tube). If it has not been
established by the regulatory test or standards, the value for the pressure
test is usually indicated by the tube manufacturer.
III.3 Elimination of static electricity
When the requirements for electric continuity must be taken into account,
the recommendations for assembly furnished by the manufacturer should
be followed closely. Moreover, after installation of the fittings, a test should
be performed. If the tube has very low resistance, this test should be
performed by simplified equipment (for example, a “quick test”). In other
cases, an insulation controller is required.
III.4 Fixed installations
When possible, the flexible tubes used in fixed installations should be
joined by the appropriate securing device. This device should not interfere
with the normal variations in flexible tubes subject to pressure such as
length, diameter, and/or torsion. If the tubes must be used under special
conditions in terms of mechanical behavior, pressure, vacuum, or
geometry, consult the manufacturer.
III.5 Moving parts
When the flexible tubes are installed on moveable parts,ensure that the tube
is not subject to shocks, blocking, or friction due to movement, and that it is
not forced to undergo abnormal curvature, folding, traction, or torsion.
III.6 References
If not only marking, but also a reference is required on the flexible tube,
adhesive tape rings should preferably be used. If this is not possible, avoid
the use of paint. Consult the manufacturer of the flexible tube, since the
tube sheathing is not compatible with the solvents used in the painting
industry.
III.7 Maintenance
Although there are some fields of use in which there are specific
regulations,controls should be performed on all flexible tubes on a regular
basis to ensure their fitness for continuing operation. It is especially
necessary to consider the condition of the fittings and the appearance of
certain anomalies that indicate the tube has deteriorated, either due to
normal aging or aggressions related to improper conditions of use or
accidents during maintenance.
Therefore, special care should be taken to watch out for the appearance of:
- Fissures, scratches, cleavage, or ruptures in the sheathing that lead to
exposure of its framework;
- Deformation, blisters, or localized swelling when they are subject to
pressure;
- Leaks.
If these anomalies are detected, the flexible tube should be replaced.
Moreover, in certain fields of use, an expiration date has been established
for safety reasons. This date is indicated on the marking of the flexible
tube, and it should be respected even if the tube does not show apparent
signs of expiration.
III.8 Repairs
In general, repair of the tubes is not recommended. Nevertheless, in
specific cases when possible repair is considered, this must be limited
strictly to the manufacturer’s recommendations for the tubes. Moreover,
following repair, a pressure test should be performed. If there is
deterioration due to a cut on one end, and the length of the tube that is
still in food condition is sufficient, the tube can be repaired by cutting off
the defective part.
PART B: SUPPLEMENTARY RECOMMENDATIONS FOR
SPECIFIC APPLICATIONS
I STEAM
In addition to the general recommendations furnished in PartA, there are
some specific points that must be described in detail.
The tubes included in the manufacturer’s catalogs are generally planned
for transport of wet steam. In this case, there is a direct relationship
between temperature and pressure. When overheated steam or water
are conveyed, consult the manufacturer of these tubes as in such cases
there is no direct relationship between temperature and pressure, and the
tube must withstand different conditions. Moreover, if operation is not
continuous or there are cooling phases in the operation cycle, the tube is
subject to thermal shocks that can lead to a phenomenon known as
“popcorning”.
POPCORNING:
It must be taken into account that the steam is diffused through the walls
of the tube. This explains why the steam tubes are usually constructed
with a sheathing that has been marked off to facilitate diffusion and thus
prevent the development of ruptures in the sheathing.
- Development of phenomenon:
If circulation of the steam is interrupted or the temperature or
condensation decreases during the cooling phase, then the pressure inside
the tube decreases.
If the temperature rises, the water evaporates again, leading to increased
pressure. Due to the ongoing effect of these thermal shocks, swelling and
localized explosions may develop in the tube. Since they resemble the
bursting of grains of corn, this phenomenon is often referred to as
“popcorning”.
I.2 Installation
Depending on the operating temperature, suitable measures and technical
precautions should be implemented in order to protect the personnel
and prevent the consequences of an accidental explosion of the flexible
tube.
II FOOD AND FOOD PRODUCTS
In this field of use, the flexible tubes are generally subject to the regulatory
requirements based on the type of components and the chemical inertia
that occurs depending on the products to be conveyed. Therefore, it is
necessary to ensure that the flexible tubes comply with these
requirements. Moreover, the regulations often require standards for
cleaning and sterilization of flexible tubes. The user is fully responsible for
the type of cleaning products as well as the frequency of cleaning.
III ABRASIVE PRODUCTS
For optimum duration, the flexible tubes should be maintained as straight
as possibly and unnecessary curves should be avoided. Therefore, larger
bending radiuses must be used since, if the radius is too small, it will cause
undesirable turbulence inside the tube. Moreover, it is necessary to
control the electrical conductivity that, in this kind of tube, is ensured by
an effective disposal of the loads of static electricity generated by the
friction of the particles conveyed against the wall of the tube.
As for the fittings, the outer ones should not be subject to abrasion.
Moreover, the joints in the tubes prevent the formation of turbulence
which, as mentioned previously, leads to high consumption in unsuitable
conditions.
IV CORROSIVE OR AGGRESSIVE PRODUCTS
These include acids, bases, solvents, agricultural, and pharmaceutical
products as well as other chemical products. Whenever the products are
not included in the list of compatible products furnished with the technical
documentation, or the temperature and concentration limits are not
within the acceptable parameters, the tube manufacturer should be
consulted. Stagnation of fluids inside the flexible tubes, particularly
solutions or emulsions, should be prevented, since the resulting
decantation leads to concentrations that may surpass the permissible
limits. In order to prevent this, the tubes should be cleaned and rinsed
after each use,as described in paragraph 3.4 or Part A. It is particularly
important to take all necessary technical precautions in order to prevent
leaks caused by accidental explosion of the flexible tubes.
V INFLAMMABLE PRODUCTS
Such products include liquid hydrocarbons (essences, petroleum,
kerosene) or gaseous hydrocarbons (GPL). In most countries, there are
regulations for storage and transport of these products. In the field of
flexible tubes, the regulatory requirements regarding electrical resistance
should be complied with. Moreover, it is important to consider the type
and frequency of controls required to ensure their fitness for use with the
passing of time. For the hydrocarbons, it should also be ensured that the
percentage of aromatic hydrocarbons (benzene, toluene, xylene) is within
the limits established by the manufacturer of flexible tubes.