Thermoplastics: identification by burn test and welding temperatures

How to use this guide

There are more than twenty thermoplastic types, and they behave very differently when exposed to heat. This guide compiles identification, welding temperatures, and suitable methods per material so that you can select your approach before starting. The figures are indicative: the applicable DVS standard or pipe manufacturer's instructions always take precedence.

The temperatures are tool or melt temperatures, not the melting point. Heating mirror refers to the surface temperature of the mirror, hot gas refers to the air temperature exiting the nozzle, and for extrusion, melt temperature and air temperature are specified separately.

For PE and PP pipes, specific welding parameters can be found in the welding tables, pipe classes are explained in SDR, PN and pipe classes, and manufacturer-specific tables are located in butt welding parameters from pipe manufacturers.

Burn test: field identification

A burn test is the quickest way to distinguish between materials when markings are missing. Take a small shaving with pliers, hold it in the flame for a couple of seconds, and observe the flame, soot, dripping, and odour. Work outdoors or with extraction, as PVC and PTFE emit hazardous gases.

The burn test is an indication, not an analysis. In case of doubt, and always when welding pressure-bearing systems, the material must be verified from the pipe marking or via the supplier.

Welding temperatures and methods per material

The table shows the temperatures normally used and which methods produce a viable joint. A field with dashes indicates that the method is rarely used for that material, not that it is prohibited.

The three most commonly used types

PE (polyethylene) is the standard for water, gas, and wastewater. PE100 is the most common pipe grade today. PE is tough, impact-resistant, and frost-tolerant.

PP (polypropylene) withstands higher temperatures and more aggressive chemicals than PE, and is frequently used in industrial applications and drainage.

PVDF is the most chemically resistant of the common types and is used in food processing, pharmaceuticals, and corrosive industries. PVDF requires stricter cleaning and temperature control during welding.

PE and PP: the materials you encounter most often

PE 80 is typically butt welded at 200-220 °C, whereas PE 100 is welded at 220 °C with a shorter changeover time because the material is stiffer and less prone to flow. Pre-insulated pipes such as ProFuse differ at 240 °C because the protective jacket participates in the process. Read more in butt welding of pre-insulated pipes.

PP is butt welded at 210 °C with a tolerance band of +/- 10 °C. For extrusion welding, melt temperatures of around 220 °C and air temperatures of around 280 °C are used for both HDPE and PP.

In electrofusion welding, the fitting's parameters control the cycle, not the pipe material. This is explained in electrofusion fitting welding.

Materials requiring special conditions

POM: hot gas welding requires nitrogen as a shielding gas because the material releases formaldehyde when heated. Work with extraction and avoid inhaling the fumes.

PVC-U and PVC-C: welding releases hydrochloric acid, which corrodes tools and is harmful to inhale. Use local extraction at the workstation and clean tools after use. PVC also requires special attention to the temperature range, as the material degrades rapidly above approx. 200 °C.

PTFE: cannot be fusion welded like other thermoplastics. PTFE components are joined mechanically or with IR, and heating above approx. 300 °C releases toxic fluorine-containing fumes.

PA and PC: both absorb moisture, which causes voids and reduces weld strength. Dry the welding rod and components according to the manufacturer's instructions before welding. PC is also stress-sensitive: long welds and rapid cooling lead to cracking, and post-weld annealing may be necessary.

PP: the surface must be scraped and cleaned with alcohol immediately prior to welding. Without this treatment, you will obtain a joint that looks fine but lacks bond strength.

Matching material and conditions

As a rule of thumb, always weld identical materials together: PE to PE, PP to PP. Mixing materials results in a weaker joint or cracking over time.

If you want to know what can be welded together – and where a joint is only possible with limited strength – try the tool what can be welded together, where you select two materials and receive an assessment. There is also an explanation of the difference between PE 100 and PE 300.

When welding in cold conditions, the material must be thermally conditioned and dried, and welding parameters adjusted. Manufacturers' welding programs account for the material type.

Temperature and chemical resistance

PE for daily operation is typically suitable up to approximately 40 degrees Celsius continuously, PP up to approximately 80, and PVDF up to approximately 120. For corrosive media or foodstuffs: always check a chemical resistance list from the manufacturer or consult an expert.

The remaining thermoplastic types, their burn test, and welding temperatures are compiled in thermoplastics: identification by burn test and welding temperatures. Pipe data including wall thickness and weight per SDR can be found in pipe data: wall thickness and weight.

From material selection to parameters

If you need to weld two different materials together, you can check the combination in the tool what can be welded together. Once the material is known and approved, proceed to pipe diameter, SDR, and the table corresponding to the material.

For PE and PP pipes, times, pressures, and temperatures can be found in the welding tables. For pre-insulated pipes and specialty materials, we refer to the manufacturer's own table, the most important of which are compiled in butt welding parameters from pipe manufacturers.

If a component in PE, PP, PTFE, or POM cannot be fusion welded, solvent cementing or adhesive bonding is an alternative, but the materials require surface preparation. Read how in bonding of PE and PP.