Fire exit. Credit: Colourbox

Improved coatings for fire protection

Tuesday 18 Aug 20
|
by Morten Andersen

Contact

Søren Kiil
Professor
DTU Chemical Engineering
+45 45 25 28 27

Contact

Claus Erik Weinell
Senior Executive Officer
DTU Chemical Engineering
+45 93 51 15 32

Contact

Huichao (Teresa) Bi
Assistant Professor
DTU Chemical Engineering
+45 45 25 29 54

New Test Center

Recently, a new facility has been added to the experimental portfolio of CoaST. At Hundested, the CoaST researchers are able to operate rafts which can be subjected to real-life fouling and corrosion.

“It is quite unusual for a university to operate a real-life test facility like this,” says Assistant Professor Huichao Bi. As a corrosion expert in CoaST, she will use advanced microscopy to spot early signs of degradation in coating-protected steel surfaces.

“We are among the very few people in the world who have applied this technique—Scanning Acoustic Microscopy (SAM)—for the coatings study. Importantly, based on this, we are developing methods which are non-destructive for the coatings performance evaluation, meaning we will be able to study the same samples repeatedly and follow the propagation of failures over time,” says Huichao Bi.

Improving the sustainability of coatings able to dampen the destructive consequences of a fire is an example of the highly interdisciplinary coatings research at DTU Chemical Engineering.

Coatings for passive fire protection are like airbags in a car. They remain idle for years, but when the accident suddenly takes place, they absolutely need to work. Making these so-called intumescent coatings more sustainable is an example of the complex challenges faced by the researchers at CoaST (The Hempel Foundation Coatings Science and Technology Centre) at DTU Chemical Engineering.

“The main driver here is health concerns. All the many benefits of passive fire protection aside, we have to recognize that the current products do contain substances which have been shown to be carcinogenic or other-wise problematic to human health,” says Associate Professor Søren Kiil.

Intumescent coatings are mainly used for steel structures. At elevated temperatures, an intumescent coating will swell by as much as 40 times into a foam which will quickly stiffen and become char. The layer of chars thermally insulating, meaning that the inevitable heating of the steel takes place at a significantly reduced pace. Without this protection, the steel could quickly loose strength leading to collapse of the structure.

Passive fire protection may save lives

Intumescent coatings exist in two classes, one for normal buildings and one for more critical infrastructure like oil rigs. The presence of hydrocarbons triggers more violent fire development. Therefore, coatings for this purpose need to respond faster.

The first intumescent coatings were invented around 100 years ago. Since then, these coatings have been improved in various ways, but the interest in developing more sustainable formulations is relatively new.

An example of a problematic substance found in intumescent coatings is zinc borate. The researchers in CoaST have ideas for less hazardous alternatives. However, the question is whether the technical properties will still live up to specifications. At an oil rig, for instance, lives may well depend on intumescent coatings. The coating will not put out the fire, but it will dampen the effects and give personnel time to evacuate.

“We want to develop more environmentally benign coatings, but we cannot compromise safety. We need to be sure that our sustain-able alternatives will still function after say 15 or 20 years,” says Claus E. Weinell. As Senior Executive Officer he is responsible for experimental facilities in CoaST.

A recent initiative is specially developed table-size electro-ovens for the experiments.

“Traditionally, coatings are tested in big industry-type ovens. We realized that smaller electric ovens would be better for our research. They can be heated up and cooled down much faster than larger ovens. Furthermore, we can obtain better control of the conditions and thus more accurate results. And finally, we simply save energy consumption and costs by doing the experiments in smaller ovens,” Claus E. Weinell states.

Accelerated testing is imperative

Obviously, the researchers cannot wait for 15 years to see if the properties are still according to specifications. Therefore, accelerated tests are a key part of their setup. An example is cyclic weathering, where the temperature is raised and lowered repeatedly.

“In this way, we increase the driving forces which create degradation of the coating under real-life circumstances,” explains Claus E. Weinell, continuing:

“However, we need to constantly be alert to possible differences between what goes on in the accelerated tests relative to the real situation. We need to understand both the physics and the chemistry involved. This can only be achieved through a constant interplay between experiments, mathematical analysis, modelling and simulations.”

Even so, there is still a limit to how much testing can be accelerated:

“If we overdo the accelerated weathering, we will induce phenomena which are different from what is seen in real applications. There-fore, we still need relatively long time spans, typically some months, for the experiments.”