Chemical Storage Extrusion-Wound Polypropylene (PP) Tanks

Polypropylene (PP) Tank Technical Specifications

Polypropylene (PP) extrusion-wound tanks are engineered for high-temperature, highly aggressive chemical service where standard HDPE (120 °F) and XLPE (150 °F) fail. These tanks are specified for demanding municipal and industrial duty where long-term integrity, repairability, and corrosion resistance are non-negotiable.

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1. Material & Manufacturing Specifications

Polypropylene extrusion-wound tanks derive their performance from both the base resin and the manufacturing method. Together they deliver exceptional rigidity, chemical resistance, and long-term reliability.

Specification Area	Detail
Material	Polypropylene (PP, sometimes referred to as PolyPro) is selected specifically when the operating temperature and chemical aggressiveness exceed the practical limits of HDPE (~120 °F) and XLPE (~150 °F).
Manufacturing Process	Extrusion-wound plastic construction, creating very rigid, highly uniform tank walls. The extrusion-wound shell eliminates the bulging, “elephant foot,” and inconsistent wall thickness often seen in thin-walled rotationally molded tanks.
Design Standards	Engineered and designed to the German DVS 2205 standard and related EN 12573 guidelines, which incorporate: Long-term hoop stress calculations Wind and environmental loading Nozzle and manway reinforcement Temperature effects up to ~60 °C
Structural Integrity	Thick, engineered wall structure produces a very rigid tank that maintains dimensional stability over time and under load. The design avoids common field failures like sidewall creep and bottom “flaring.”
Wall Thickness	Typical wall thickness ranges from ½ inch to 3.5 inches, with the extrusion process capable of producing sections up to approximately 6 inches where required by design.
Repair & Modifications	Polypropylene extrusion-wound tanks are fully weldable. Nozzles, manways, and accessories can be added or modified in the field, and structural repairs can be performed by certified thermoplastic welders—a key advantage over non-weldable crosslinked PE tanks.
Color & Maintenance	Color is added directly into the resin as a permanent additive, so there is no coating to strip, sandblast, or repaint. Tanks are essentially maintenance-free from a coating standpoint.
Quality Control	Fabrication is performed by certified thermoplastic welders with documented procedures. Each tank undergoes a minimum 24-hour hydrostatic test; air testing or alternative acceptance testing is available upon request.
Expected Service Life	When specified and installed correctly for the chemical, temperature, and load, extrusion-wound PP tanks are designed to be long-life assets, often targeting 20+ years of service.

DVS 2205

Extrusion-wound

Certified welders

24-hour hydro test

2. Performance Specifications (Thermal, Chemical & Pressure)

PP tanks are chosen for applications where both temperature and corrosive exposure are beyond the safe range of most plastics and many metallic systems.

Specification Area	Detail
Chemical Resistance	Polypropylene offers broad chemical immunity across pH 0–14, handling strong acids and alkalis with very low moisture absorption and high resistance to staining or embrittlement. This includes aggressive oxidizers and reagents commonly found in municipal and industrial treatment.
High-Temperature Chemical Service	Recommended for continuous chemical service up to approximately 180 °F, including high-concentration acids such as 98% sulfuric acid when maintained below the specified temperature limits and as validated by the tank manufacturer.
High-Temperature Water Service	Suitable for continuous water service up to ~200 °F, assuming proper mechanical design and support in accordance with DVS 2205 and the manufacturer’s recommendations.
Pressure / Vacuum Rating	Tanks are designed primarily as atmospheric vessels. Typical allowable additional internal pressure is: Up to ~1 PSI induced pressure under standard design Up to ~2 PSI where additional structural reinforcement is provided Elevated temperature reduces allowable pressure and vacuum—engineering review is required for any non-atmospheric conditions.
Specific Gravity / Load	Tanks are engineered to the specific gravity of the stored liquid, with high tensile and compressive strength in the wall structure to safely manage heavy solutions and slurries.
External Environment	PP tanks incorporate UV stabilizers and are highly resistant to ambient UV, acid rain, and most outdoor atmospheric conditions. The material is dielectric and does not readily absorb or conduct heat within its operating range.

pH 0–14

Up to 180 °F (chemicals)

Up to 200 °F (water)

Atmospheric + low-PSI only

3. Design Options & Accessories

The rigidity and weldability of extrusion-wound PP tanks provide exceptional flexibility for size, geometry, and accessory integration.

Specification Area	Detail
Capacity Range	Custom-engineered tanks from approximately 50 gallons up to 50,000 gallons: Rectangular tanks available up to ~18,000 gallons Vertical cylindrical tanks up to ~50 feet tall
Shapes & Configurations	Manufactured in cylindrical (vertical) and rectangular forms. Rectangular designs can significantly reduce freight and fit tighter footprints, sometimes saving up to ~80% on freight vs. multiple round tanks.
Top Options	Open top Flat top Cone top Recessed top Selected based on process access, head space, and containment requirements.
Bottom Options	Flat bottom Slope bottom Cone bottom Used to optimize drainage, solids removal, and cleaning.
Double-Wall Containment	PP tanks can be fabricated as double-wall systems (inner tank inside an outer tank), fully welded together to provide integral secondary containment. Typical details include: Interstitial monitoring ports Drainage provisions for the outer tank Leak detection instrumentation as required
Fittings & Flanges	Tanks can accommodate as many fittings as design permits, including: 150# and 300# ANSI flanges Threaded or stub-end style connections as appropriate Nozzle reinforcement is engineered per DVS and manufacturer rules.
Mixing & Heating	The rigid wall allows mixer mounts (poly or steel) to be installed directly on the tank without external superstructures, when designed correctly. Internal immersion heaters or external heating coils can be provided to maintain process temperature.
Access & Safety	Typical options include: Fiberglass or steel OSHA-compliant ladders (with/without cages) Handrails and kick plates around tops Top and side manways for entry and cleaning Side manways are particularly useful in constrained spaces where top access is limited.
Monitoring & Instrumentation	Tanks can be outfitted with: External visual level indicators (e.g., reverse float style) Electronic level transmitters and switches Emergency pressure / vacuum relief devices Instrument nozzles are located to protect devices and maintain code compliance.

50–50,000 gal

Vertical & rectangular

Double-wall available

Mixer-ready tops

4. Installation & Site Requirements

Correct installation is critical to achieving the full design life of an extrusion-wound PP tank. Foundation, anchorage, and piping must all be engineered as part of the system—not treated as afterthoughts.

Specification Area	Detail
Foundation / Pad	Tanks must be installed on a very flat, very clean reinforced concrete pad. The pad must be fully level and free of any rocks, pebbles, or debris that could create point loads and lead to cracking or localized stress.
Footprint / Footings	The concrete footing or slab should extend at least 1.5 feet beyond the tank diameter in all directions to: Accommodate hold-down brackets and anchors Allow for thermal expansion and contraction of the tank shell
Outdoor Installations	For outdoor tanks, the design must consider: Site-specific wind loads and gust factors Seismic / earthquake requirements (where applicable) Hurricane exposure, snow, and other environmental forces Proper tie-down / anchoring systems are required, often with stamped engineering calculations. Lightning protection (rod or grounded conductor) should be considered for tall tanks.
Piping Connections	To avoid stress cracking at fittings, all connections should incorporate flexible hose or expansion joints so the tank can expand and contract independently of rigid piping. Rigidly connected straight pipe runs should be avoided at the tank shell.
Commissioning	Filling and pressurizing should follow manufacturer procedures, including staged filling where appropriate, inspection of all nozzles, and verification of leak-tightness after the 24-hour hydro test or site acceptance test.

Properly designed, installed, and maintained polypropylene extrusion-wound tanks provide a robust alternative to steel and standard poly, especially where high-temperature, high-corrosion, and long-life expectations intersect.