Until When Is It Safe To Continue Operating GRP Tanks Without Replacing Them?
Tanks and pipelines made of glass-fibre reinforced plastic (GRP) are extremely popular in plant construction. The reason for this is the material’s high resistance to a variety of aggressive media. Components made of GRP are therefore particularly suitable for use in the chemical industry.
Over the years, however, various influences can impair its serviceability. This is because the components are constantly subjected to chemical, thermal and mechanical stress – which naturally leaves corresponding traces in the long run. 200,000 operating hours – about 23 years – is the calculated service life of GRP tanks.
GRP is only one fifth as dense as steel, but it can withstand high mechanical loads. It consists of a multi-layer, very strong laminate with low weight. Another advantage is that more flexible geometries are possible during production than with components made of other materials. Plant operators benefit not only from the particularly long service life but also from the material’s nominal mechanical values, which enable high load inputs and the absorption of large agitator loads. With these and other properties, constructions made of steel perform noticeably worse.
Condition Assessment Of Durable GRP Tanks And Pipes
For an effective condition assessment of a GRP tank, both an external and an internal visual inspection are necessary. This can reveal various damage patterns, such as cracks or deformations – but also the so-called osmotic blistering. These changes are caused by the penetration of the medium into the laminate, where it exposes the glass fibres and can also attack the substance through acids or alkalis that form. If the process progresses, the glass fibres can even dissolve completely, resulting in the destabilisation of containers. It is important that operators of industrial plants receive a reliable basis for decision-making with such detailed tests.
If even clearer, more detailed statements on the condition of the glass fibres in the material are required, the use of a scanning electron microscope coupled with an energy dispersive X-ray analyser (SEM-EDX) makes sense. This requires very little sample material so that a diameter of 20 to 30 mm is sufficient for the core hole. It is also advantageous that the very small holes created by sampling can be closed again with little effort. It is certain that with proper inspection, GRP components can be operated even after their expected service life. Service providers can make recommendations on further operation, replacement or refurbishment by means of laboratory analysis.
This text is based on a longer article in the trade journal “CHEMIE TECHNIK” from March 2021.
