The chemical industry is responsible for transforming raw materials into valuable products and is widely regarded as one of the most important sectors of the economy. The aggressive and hazardous nature of the chemicals involved in these processes requires robust and reliable engineering solutions. Sealing solutions are one of the most important components in ensuring that chemical plants are safe, efficient and environmentally friendly.

The chemical industry is a complex combination of processes and operations that utilize chemistry to manufacture a variety of products. These processes use a wide variety of raw materials to produce a wide range of primary, secondary and tertiary products. Primary products are the furthest removed from the key users, and demand is often obscure, as each product passes from one process to the next before appearing on the market.
In general, the chemical industry is divided into the following areas:

• Basic Chemicals
  Fine Chemicals
  Specialty Chemicals
  Inorganic chemicals
  Organic Chemicals

Each area of the production process requires unique assets and applications to withstand the aggressive nature of the raw materials as they are transferred from one state to another (see Figure 1), thus requiring the specialized development of sealing solutions.

PTFE gaskets are often a reliable choice for sealing in chemical processes.

The Importance of Sealing

Seals play a pivotal role in chemical processing. By preventing the leakage of liquids, gases and other materials, seals ensure that no harmful substances can seep into the production process or have a negative impact on the surrounding environment.

In addition to safety, seals are critical to safeguarding process efficiency. They help regulate key parameters such as pressure, temperature and flow rate, which directly affect the consistency and quality of the production process. Seals ensure optimal operating conditions, increasing productivity and reducing operating costs. In addition, as a protective barrier, sealing solutions significantly extend equipment life, minimize wear and tear, and reduce the need for frequent maintenance or replacement, ultimately leading to long-term cost savings and increased operational reliability.

Seal type and material selection

Therefore, the chemical compatibility of the seal with the system fluid is critical to achieving reliable and durable sealing performance. Because the polymers and other raw materials used in seals vary widely in the way they react with chemicals in the fluid, the selection process can be extremely challenging, especially when relying solely on chemical compatibility charts.
For example, when a particular chemical interacts with certain materials, the chemical can “attack” the polymer bonds, thereby reducing the performance of the polymer. In some cases, the chemical precipitates components from the polymer, thereby weakening the polymer or stripping it of its essential mechanical properties. Other chemicals may penetrate the polymer, causing it to swell. Depending on the application, this swelling may be beneficial or detrimental. In some cases, the media may not affect the polymer at all. Rather, it may have a negative effect on one of the other raw materials used in the sealing material, leading to reduced mechanical properties and potential failure.
The wide variety of processes and chemical media used in the chemical industry means that there is no “one size fits all” option when it comes to sealing. Most chemical plants utilize a variety of sealing solutions. These include.

• elastomer ：Made from a variety of different polymers such as Nitrile Rubber (NBR), Ethylene-Propylene-Dimethylene Rubber (EPDM), Silicone, Neoprene, Fluorocarbon Rubber (FKM), etc.; these seals can be used in a variety of applications in the form of gaskets, O-rings and specialty molded seals.
• Compression Fiber：These materials consist of combinations of elastic binders, synthetic, organic and/or inorganic fibers, and other ingredients, and are commonly used in a variety of general-purpose services.
• Flexible graphite ：Graphite seals are chemically expanded into rolls or sheets that offer excellent chemical resistance while withstanding higher temperatures than rubber seals. Many graphite seals also feature a metal reinforcement, making them even stronger and able to withstand higher working pressures.
• PTFE：PTFE is probably the most commonly used material for chemical process sealing solutions, providing excellent chemical resistance even in the most aggressive media.
• metals ：Metal-based sealing solutions are more common in applications with extremely high temperatures and pressures, but still have their place in chemical processing plants. These seals are made entirely of metal, or a combination of a metal carrier element and a softer sealing element such as graphite or PTFE, and are used to some extent in virtually all industrial manufacturing plants around the world.

Pros and Cons

There are many options for sealing solutions, and choosing the one best suited for a particular application can be challenging. Safety is critical as many of the raw materials used in chemical processing facilities are aggressive and have low tolerance. The ideal solution should provide safe and reliable sealing performance throughout the process until the next scheduled maintenance. Working closely with an experienced manufacturer or supplier of sealing products can be a valuable asset to any chemical plant.

In general, it is important to remember that each sealing solution has its own advantages and disadvantages. For example, elastomeric seals can form a seal at lower loads than most other seals. They are also relatively inexpensive. That's great, right? Well, don't jump to conclusions either. They can be crushed at lower loads than other seals, degrade faster over time (especially at elevated temperatures), and exhibit a high degree of relaxation, which means they don't hold loads as well. Depending on the polymer, their compatibility with various media varies greatly.

On the other hand, PTFE-based seals can withstand some of the most aggressive chemicals on the planet. They are often considered to be flexible materials that adapt well to flange imperfections and have an indefinite shelf life. These are great qualities and characteristics. The main disadvantages of PTFE seals are their higher cost and the fact that in its raw form PTFE is highly susceptible to creep relaxation.
Choosing the right sealing solution for an application requires careful consideration of many of these variables. Sometimes, rubber seals are the right choice. Sometimes a graphite plate, compressed fiber plate or PTFE plate may be the right choice.

作者：TEADIT泰迪集團 Angelica Pajkovic 與 Chris Morris

原文鏈接：

https://teadit.com/us/article/the-crucial-role-of-sealing-solutions-in-preventing-chemical-leaks/