Gaskets: meeting the acid test in sealing

Dow Corning Corp. was experiencing difficulties sealing a large hydrochloric acid column. GORE-TEX Series 600 gasket tape proved it could seal tightly for an extended period of time.

By Steve Beach, Dow Corning Corp., and Rob Haywood, W.L. Gore & Associates

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Dow Corning Corp., Midland, Mich., a leading producer of siloxane intermediates, was experiencing continuous difficulties sealing a large, glass-lined, steel hydrochloric acid column at its Carrollton, Ky., facility. The proper operation of this piece of equipment was critical to the operation of the entire plant. The entire process could not run without this column.

Dow Corning’s maintenance staff was concerned that leaks were being encountered during every shutdown – it was obvious that the PTFE envelope-style gaskets being used to seal the hydrochloric acid column were not solving the problem. Experience with the envelope gaskets showed that the process media permeated through the envelope, thereby corroding the gasket insert and compromising its ability to seal the joint and the column.

While installing Belleville washers to hold loads in the column constant in July 2000, staff discovered that the flange on the acid column was again leaking; further tightening did not stop the leakage. The gasket had to be replaced. This time, an alternative to the PTFE envelope gasket design was sought, not only because a reliable seal could not be made, but the delivery time for other gasket alternatives would be too long (a lengthy outage would have had a significant, negative impact on the plant).

After considering several alternative gasket designs, Dow Corning called upon the Sealant Technologies Group of W.L. Gore & Associates, Elkton, Md., to evaluate the possibility of applying GORE-TEX gaskets to seal the hydrochloric acid column. After analyzing the Carrollton plant’s requirements and application parameters, Gore technicians recommended the GORE-TEX Series 600 gasket tape for this service.

GORE-TEX Series 600 gasket tape is a unique, patented, form-in-place sealant with tensile strength oriented in all directions, which gives the gasket dimensional stability for better sealing reliability for a longer period of time. The key to its performance is the gasket’s ability to maintain its original width in addition to a thick profile to compensate for flange deviations. Under compression, the expanded PTFE creates a very tight seal as the gasket’s microstructure “locks” together while conforming to all flange imperfections.

The gasket tape was installed in all but one of the acid column flange connections. At the time, the bottom connection wasn’t leaking; because it was Dow Corning’s first experience using this particular gasket material, there was reluctance to change the bottom PTFE envelope gasket.

In addition to the promise of better sealing performance, gasket availability and installation speed were highly valued. Working with Dow Corning maintenance personnel, a Gore field engineer installed the gasket tape during a weekend. The onsite technician helped double-check gasket load calculations, as well as provided assistance joining the tape and determining if any shimming was needed. The ability to make long, single-piece runs when installing the tape proved to be a benefit, both in terms of shortening the installation time and in obtaining better sealing reliability. Two people were able to lay the tape in place quickly and efficiently.

Following gasket installation, the hydrochloric acid column was pressurized, and a leak-detection agent sprayed on all the flanges to ensure that a tight initial seal had been achieved. This proved to be successful.

For the same or lower initial cost, coupled with short-order lead times, Dow Corning maintenance engineers hoped to realize a higher level of sealing reliability. The criterion for success was simply to hold the seal for a long time.

Nearly two years after the hydrochloric acid column was sealed, a leak was detected -- it turned out to be the bottom PTFE envelope gasket. In May 2002, the column was shut down to stop the leak. At that time, careful inspection of the GORE-TEX gaskets showed that they were still performing well. Periodic visual inspection continues to find reliable, leak-free performance.

For Dow Corning, the GORE-TEX Series 600 gasket tape had proved its ability to seal tight – and stay tight -- for an extended period of time. The gasket tape is now used on all five connections. More than 30 months after the tape was installed on the last connection, the column flanges continue to be leak-free. As a result of this experience, Dow Corning has expanded its use of GORE-TEX gasket tapes to seal similar applications, as well as other columns.

Steve Beach is a reliability engineer for Dow Corning, Carrollton, Ky. He is responsible for maintenance and reliability of lined equipment at the Carrollton plant. Rob Haywood, BSCE, MBA, is a fluid-sealing and gasket specialist for W.L. Gore & Associates, Elkton, Md. E-mail him at rhaywood@wlgore.com.

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