DEVELOPMENT OF STATIONARY METAL BELLOWS SEAL

In addition to elastomer bellows seal, non contacting mechanical seal and pump seal, stationary metal bellows seal are also common seals in industry. The following content introduces the development process of stationary metal bellows seal.

Invention Process of Stationary Metal Bellows

The stationary metal bellows seal we know today was developed by Exxon Mobil in the 1970s. Exxon Mobil was not satisfied with the reliability and performance of the seals in the hot oil services because the oil decomposed and locked the rotating flexible sealing elements. Since January 1976, Exxon Mobil has designed, manufactured and assembled a prototype of a stationary metal bellows seal using parts from different seal manufacturers.

In the 1970s, Exxon Mobil refineries still used gland packing to seal the pumps in their plants, especially those with higher temperatures. In order to improve the reliability, the staff replaced the gland packing with mechanical seal. Hot pumps were a definite challenge and required a metal bellows to attain the necessary temperature rating. For the most part, the refinery was using Chempro (now Sealol) Type 605 rotating metal bellows seals in hot services. These sealing elements are custom-made to suit the particular pumps and they are often welded directly to the sleeve bellows. Even so, unless a cold external flush (plan 32) is injected into the seal chamber, the average maintenance interval is only 3 to 6 months. However, the installation and operation cost of plan 32 is high, which is not desirable.

In Exxon Mobil, there is a team called pump team, whose job is to carry out detailed fault analysis of all pumps repaired in the repair shop. Although almost all seals at that time were rotary spring seals, they began to notice that stationary seals tended to be more reliable.

One day, they were examining a high temperature Borg-Warner (now Flowserve) Type H seal that, according to their records, had served for several years in a high temperature service. Although the Type H is a push rod seal, it is fixed and installed with asbestos U-shaped gasket. They could not get parts for the Type H so it was replaced with a Chempro (became Sealol) Type 606 which was a new product developed by Chempro to be more adaptable. However, the Type 606 was a rotating bellows seal. When they examined the Type 606, they found that it became very inflexible.

After that, they asked several seal OEMs about stationary high temperature seals, but the manufacturers were not interested and no one provided anything. As a result, they decided to build their own prototype of a stationary metal bellows seal.

The very first prototype high temperature metal bellows seal was designed and assembled by John Eeds. It used a Chempro Type 606 as the stationary bellows and a Chempro “floating seat” as a rotating mating ring. 

The pump team tested 19 different prototypes before deciding to hand over the design and results to the seal manufacturer. Some researchers want to patent the technology, but others think that seal OEMs will better develop the concept commercially.

At the time, Exxon Baton was doing very little business with Borg-Warner Seal Division and Borg-Warner took this opportunity to gain new business. They expressed an interest in making stationary bellows seals and requested a meeting to discuss the Exxon needs.  A meeting was arranged with the pump team. 

After some discussion and negotiation, Borg-Warner Seal Division placed an order for several sizes of the stationary metal bellows seal. Of course, this purchase quickly gained the attention of other seal manufacturers. In this way, the stationary metal bellows seal has been widely used.