Elastomer/Plastic degradation

Prevention or Remedial Action

Failures of plastic and elastomeric materials generally occur as a result of:

1. mechanical stress
2. effects of chemical moisture degradation
3. effects of temperature.

The latter two effects generally result in either a loss of mechanical strength (i.e. softening) loss of ductility (i.e. embrittlement), swelling or explosive decompression (i.e. failure from internal expansion of gas upon pressure decompression).

Standard Test Methods

• proper selection of resin for resistance to environment, temperature and pressure cycles.
• use of reinforcements to improve mechanical performance and limit chemical attack
• use of multi-ply construction with barrier layer of chemically resistant material.
• design of seals to minimize extrusion and limit contact with enviroment
• replace with corrosion resistant metallic components

1. Elastomers

• NACE TM0187 (sour gas)
• ASTM D-3632 (accelerated aging)
• ASTM-2934 (compatibility with service fluids)
• ASTM C-1083 (water absorption)

2. Plastics

• ASTM D-1870 (heat aging)
• ASTM D-4363 (accelerated weathering)
• ASTM D-4350 (corrosivity index for plastics and fillers)
• ASTM D-543 (chemical resistance)
• ASTM D-570 (water absorption)
• ASTM D-5045 (fracture toughness)

3. Composites

• ASTM D-4762 (selection for automotive/industrial applications)
• ASTM D-4102 (oxidative resistance)

Standard mechanical test on elastomer, plastics and composites.

Evaluation of Plastics Elastomers

In general, plastics and elastomers are used because they provide specific mechanical, physical or anti-corrosive properties. Therefore, an evaluation of performance of these materials usually involves determining their chemical compatibility and thermal stability in the service environment. Tests on plastics and elastomers usually involve the use of post exposure physical and mechanical property measurements and visual examination of physical changes (e.g. blistering, fissuring, swelling) to rate their resistance to the corrosive environment. Another important aspect of the evaluation of these polymeric materials is the use of service life testing methodologies. In their simplest form, these take the form of evaluations of performance after multiple exposure period instead of the commonly used single point testing. This allows for the tends in performance properties to be obtained as a function of exposure time. Additionally, the use of theoretical and empirical models can be used to evaluate test data. For example, short term failures obtained at multiple test temperatures can be used to predict longer term serviceability in various service environments at temperatures below the test temperature.