Why Chemical Resistance Matters in Flange Spacer Selection

Flange spacers are installed directly between pipe flanges in the flow path of a system. In chemical processing, water treatment, pharmaceutical manufacturing, and other corrosive environments, these spacers are constantly exposed to aggressive media — acids, caustics, solvents, oxidizers, and more.

A spacer made from the wrong thermoplastic will degrade over time, losing dimensional integrity, sealing performance, and structural strength. The consequences range from minor leaks to catastrophic flange joint failure. Choosing a chemically compatible material from the start is the most cost-effective decision you can make.

The Three Primary Thermoplastic Materials for Corrosive Service

SG&P manufactures thermoplastic flange spacers in three primary materials, each with distinct chemical resistance profiles:

PVDF (Polyvinylidene Fluoride)

PVDF is a high-performance fluoropolymer that offers outstanding resistance to a broad range of aggressive chemicals. It combines excellent chemical resistance with high mechanical strength, making it one of the most versatile materials for demanding industrial applications.

Key properties:

• Resistant to most acids, including hydrochloric, sulfuric, nitric, and hydrofluoric acid
• Excellent resistance to halogens such as chlorine, bromine, and fluorine
• Service temperature range: -40°F to 280°F (-40°C to 138°C)
• High tensile strength and dimensional stability under load
• Good UV resistance for outdoor piping systems

PVDF is widely used in semiconductor wet processing, chemical distribution, water treatment, and pharmaceutical piping where both purity and chemical resistance are required.

PTFE (Polytetrafluoroethylene)

PTFE is the benchmark for chemical resistance in thermoplastics. It is virtually inert to all known chemicals, making it the go-to choice for the most aggressive service conditions and highest-purity applications.

Key properties:

• Near-universal chemical inertness — resistant to virtually all acids, bases, solvents, and oxidizers
• Extremely low coefficient of friction and non-stick surface
• Service temperature range: -328°F to 500°F (-200°C to 260°C)
• Excellent performance in steam and high-temperature services
• Compliant with FDA and USP Class VI standards for food and pharmaceutical applications

The tradeoff with PTFE is its relatively lower mechanical strength compared to PVDF — it has a tendency to cold-flow (creep) under sustained compressive loads. For flange spacer applications where bolt loads are high, this must be factored into the design.

Polypropylene (PP)

Polypropylene is the most economical of the three materials and offers excellent chemical resistance for a wide range of general-purpose corrosive applications. While it does not match the performance of fluoropolymers in extreme conditions, it is highly effective and cost-efficient for many standard industrial services.

Key properties:

• Excellent resistance to acids, bases, and aqueous salt solutions
• Resistant to most organic solvents at ambient temperatures
• Service temperature range: 32°F to 225°F (0°C to 107°C)
• Lightweight and easy to machine to tight tolerances
• Lowest cost option among the three materials

Polypropylene is not suitable for oxidizing acids (such as concentrated nitric or chromic acid), aromatic or chlorinated hydrocarbons, or elevated-temperature service above its rated limit.

Chemical Resistance Quick-Reference Chart

The following table provides a general guide to material compatibility. Always consult your SG&P representative or a full chemical resistance chart for your specific concentration, temperature, and pressure conditions.

Temperature and Pressure Considerations

Chemical resistance does not exist in a vacuum — temperature and pressure significantly affect how a material performs. A thermoplastic that handles a chemical well at 70°F may degrade rapidly at 180°F in the same chemical environment.

General guidance:

• As temperature increases, chemical resistance decreases — always verify ratings at your actual operating temperature
• Pressure can accelerate chemical absorption and swelling in thermoplastics
• Cycling between temperature extremes may cause dimensional changes that affect flange joint integrity
• PTFE is the most tolerant of high-temperature corrosive service; PVDF is best for high-pressure + high-chemical combined loads

Lined Pipe Systems: Special Considerations

SG&P's thermoplastic flange spacers are engineered specifically for lined pipe systems — a design where a thermoplastic liner (such as PVDF, PTFE, or PP) is bonded to the inside of a steel pipe for corrosion protection. When specifying spacers for lined pipe systems, material compatibility extends beyond just the process fluid:

• The spacer material should match or exceed the chemical resistance of the pipe liner
• Dimensional tolerances must account for the liner flange dimensions, which differ from standard carbon steel flange dimensions
• The spacer must maintain sealing integrity without being compromised by the same media the liner is protecting against

SG&P manufactures all spacers to lined pipe flange dimensions as standard, ensuring proper fit without field modification.

How to Choose the Right Material for Your Application

Use this decision framework when specifying a thermoplastic flange spacer for corrosive service:

• Step 1: Identify all chemicals the spacer will contact, including flush fluids and cleaning agents
• Step 2: Determine maximum operating temperature and pressure
• Step 3: Check compatibility against a full chemical resistance table for each candidate material
• Step 4: Consider mechanical requirements — if compressive loads are high, PVDF may be preferred over PTFE
• Step 5: Factor in budget — PP is the most economical, fluoropolymers cost more but last longer in demanding service
• Step 6: Confirm dimensional requirements for your flange standard (Class 150, 300, etc.) and pipe size

When in doubt, specify PVDF. It offers the best combination of chemical resistance, mechanical performance, and longevity for most industrial corrosive applications.