Popularizing polymers

Elaine Maslin visited with Nylacast to find out more about engineering polymers and their benefits to the offshore industry.

Nylacast component being machined. Images from Nylacast.

Engineering polymers have obvious benefits for the offshore industry – they don’t corrode, they can weigh about 1/7th the weight of steel, have a very low friction coefficient and are not affected by H2S or CO2, so-called sour gases. Engineered polymers also have an enormous plastic range, which means they can absorb impact and retain their shape. But, there are also less well-known properties – Nylacast, for example, has produced antistatic as well as conductive engineered polymers.

In the past, engineering polymers have been held back due to a lack of understanding about their properties and, therefore, potential. Not only that, but when they are being considered, the tendency is to go for PEEK – a higher grade (and cost) polymer, which can price them out of the frame.

“The advantages for engineering polymers can be significant, but they have to be viewed in a different way,” says Howard Bradfield, materials engineer, engineered products, oil and offshore, at Nylacast. Just like there are different types and grades of metals, there are many types of polymers offering different properties.

Nylacast has been producing engineering polymers since it was founded in 1967, using Nylon 6. It has made breakthroughs like Nylube, a self-lubricating polymer, now used in components like sheaths and pulleys, removing the need for lubrication and reducing weight significantly. Nylube has been used to replace bronze in marine applications offshore eliminating use of lubricants in splash zone components and on subsea mechanisms, such as clump weight sheaves.

The firm has also recently developed a new high-temperature resistant polymer, CF160, which can withstand up to 160°C and is being used as spacers in pipe-in-pipe applications, including on high-pressure, high-temperature projects, as well as for connectors and calipers.

“For high-temperature applications, CF160 can replace metals as well as higher grade polymers, such as PEEK. CF150 is marginally more expensive than nylon, but considerably less expensive than PEEK,” Bradfield says. “PEEK is an order of magnitude 10 times more expensive than Nylon.” By replacing metal with plastic in one application, the weight of a structure was reduced from a quarter of a tonne, which meant using a crane to install it, to just 100 kilos, Bradfield says.

A Nylacast nylon shroud.

“The potential is enormous,” Bradfield says, but there’s still a way to go in terms of some engineers learning how to use engineering polymers. “The current understanding of polymers is better than it was,” Bradfield says. “It is improving. When you look at ROVs 10 years ago, they all had aluminum chassis. Now the majority of the chassis and external protection is made of polymer. This can be replicated elsewhere in the industry.”

Unlike other plastics and polymers, Nylacast’s product is, as the company name suggests, cast – not injection molded or extruded. This enables the material to be annealed, which creates improved mechanical, thermal and chemical resistance properties, including higher tensile, compressive and impact strength, as well as improved resistance to creep and heat aging, due to high crystallinity and higher molecular weight, explains Malcolm Fox, head of research and development at Nylacast.

Given the possibility to vary the properties of the polymer through both the manufacturing process and introducing other chemicals into the cast material, Nylacast is also continuously looking at how to take the material further, including for higher temperature applications.

“We are interested in the behavior of material at higher temperatures, particularly creep rates [i.e. deformation],” Fox says. “What we find is design engineers are asking for more detail. So we have started a program to find out more.” Nylacast has a graduate working on a program to extend the range of measurements, such as extending the temperature range and type of measurement. For example, if a seal is being pressed against a housing under different temperature regimes, what is the creep rate going to be?

The firm has also been investing in its machining capabilities. Nylacast now has more than 100 machining centers, including five axis milling machines, as well as vintage Bridgeport machines, which still prove their worth, especially under the deft hand of an 80-year-old who has been working them for decades.

Nylon 6, or polycaprolactum, was an answer to an American firm Dupont’s Nylon 6.6 by Germany’s IG Farbe. It is a semi-crystalline polyamide, formed by ring-opening polymerization of caprolactum, an oil based product. Caprolactum has six carbons, hence the same Nylon 6, and when heated to about 533 Kelvin (259 degrees C) in an inert atmosphere for about 4-5 hours, the ring breaks and undergoes polymerization, which is then cast into blocks.

By varying the conditions of polymerization, and by adding other product, the mechanical properties of cast nylon may be altered, such as self-lubricating plastics, reduced water absorption, and antistatic plastics. There is even a magnetizable nylon, made for the food industry.