Tank Depot.com offers you a selection of materials that are by far the best suited
for molded tanks and containers for use with aggressive corrosive chemicals as well
as food products. The following is a brief description of these materials:
Polyethylene
A high quality thermoplastic that has outstanding resistance
to both physical and chemical attack. The overall general toughness and excellent
chemical resistance to a wide array of wet and dry industrial chemicals and food
products make polyethylene ideally suited for storage tanks and containers.
Polyethylene is translucent and its natural color ranges
from slightly off white to creamy yellow, depending on wall thickness and type.
Ultraviolet light stabilizers are added for use in outdoor applications. Colors
are available on request for a nominal up charge.
- Linear Polyethylene
Linear Polyethylene is available as low, medium and high
density. Most products offered in this catalog are molded of linear medium density
polyethylene (LMDPE) and linear high density polyethylene (LHDPE). They have superior
mechanical properties, high stiffness, excellent low temperature impact strength
and excellent environmental stress crack resistance. The linear polyethylene used
meets specifications contained in FDA regulation 21CFR177.1520 (c) 3.1 and 3.2 and
so may be used as an article or a component of articles intended for use in contact
with food, subject to any limitations in the regulations. Maximum operating temperature
for linear polyethylene is 140° F.
- Crosslinkable Polyethylene
Crosslinkable polyethylene is a high density polyethylene
that contains a crosslinking agent which reacts with the polyethylene during molding,
forming a crosslinked molecule similar to a thermoses plastic. This reaction improves
toughness and environmental stress crack resistance. Crosslinked Polyethylene (XLPE)
is not weldable and does not meet FDA requirement 21CFR177.1520. Maximum operating
temperature of crosslinked polyethylene is 1 50° F.
Polypropylene
Polypropylene is a rigid plastic that has a higher operating
temperature limit than polyethylene: 212° F. It offers good chemical resistance,
has a high resistance to stress crack, and is autoclavable. Polypropylene (PP) is
not recommended for applications in sub-freezing temperature or where high impact
strength is needed. A rough, irregular interior surface is common characteristic
of molded polypropylene.
Consideration of Material Selection
Elevated Temperatures
Continued or prolonged service with contents at elevated
temperatures can shorten the life of a tank. The effects of the temperature will
depend on the chemical content and its specific gravity, tank size and configuration,
material of construction, wall thickness and if there are any external supports
on the tank.
Exposure to Ultraviolet Light
Unprotected thermoplastics exposed to sunlight for an extended
period of time, absorb ultraviolet (UV) light, which can cause discolorations, embrittlement
and eventual cracking. Fluorescent lighting has a similar effect. Elevated temperatures
can accelerate the embrittling process. Tank Depot products are molded from materials
utilizing the latest technology for UV stabilizers which greatly reduce the harmful
effects of UV light. For greater protection, keep tanks out of direct sunlight or
order dark colored tanks which will further retard the effect of UV light.
Environmental Stress Cracking
Certain surface active materials, although they have no
chemical effect on polyethylene, can accelerate its cracking when under stress,
such as liquid detergents and ultra pure water- (see our chemical compatibility
Chad on pages 46 -49.) Elevated temperatures tend to accelerate the cracking. Although
all polyethylenes are subject to stress cracking, some are more resistant to it
than others. The degree of stress on the plastic has a direct bearing on its resistance,
therefore a tank and system should be designed to minimize stress. Tankdepot.com
tanks are molded visually stress free, employing materials that are highly resistant
to environmental stress cracking, and hence are less prone to cracking than fabricated
tanks. Stress cracking agents are surface active materials. Proper care should be
taken to reduce stress at fillings, bands, tie down lugs, etc.
Characteristics and Physical Properties
General Characteristics
|
Linear
|
XLPE
|
PP
|
Maximum Service Temp
|
140 F (60 C)
|
150 F (65 C)
|
212 F (100 C)
|
Chemical Resistance
|
Very Good
|
Very Good
|
Very Good
|
Stress Crack Resistance
|
Excellent
|
Excellent
|
Excellent
|
General Toughness
|
Very Good
|
Very Good
|
Fair
|
Impact Resistance
|
Excellent
|
Excellent
|
Poor
|
Abrasion Resistance
|
Good
|
Good
|
Good
|
Rigidity
|
Good
|
Good
|
Good
|
Color
|
WH Translucent
|
Off WH Trans
|
Off WH Opaque
|
FDA Compliance
|
Yes
|
No
|
Yes
|
Outdoor Use
|
Yes
|
No
|
Yes
|
Weildable
|
Yes
|
No
|
Yes
|
Recyclable
|
Yes
|
No
|
Yes
|
|
Physical Properties
(Nominal Values)
|
Linear
|
XLPE
|
PP
|
Density (gm/cc) ASTM:D1505
|
0.937-0.942
|
0.937-0.942
|
0.901-0.905
|
Environmental Stress
Cracking (F-50hrs)
ASTIM:D1693
|
>1,000
|
>1,000
|
>1,000
|
Tensile Strength ASTIM:D638
Ultimate 2"/Min (PSI) Type IV
|
2,600
|
2,600
|
3,000
|
Elongation at Break ASTIM:D638
2"/Min(%) Type IV
|
450
|
450
|
5
|
Flexural Modulus (PSI) ASTIM:D790
|
100,000-110,000
|
100,000-110,000
|
90,000-100,000
|
Brittleness Temp ASTIM:D746
|
<-94F (-70 C)
|
-180 F (-118 C)
|
32 F (0 C)
|
|