History of Glass Lining
The use of glass lining in the wastewater and sewage treatment industry began somewhat by accident. In the early 1960's, engineers with the firm Cornell, Howland, Hayes and Merryfield (later named CH2M Hill) observed that sight glass sections of piping used for monitoring the system flow were totally clear of any interior build-up, while the standard piping on both sides of these glass sections had significant build-up. This build-up and eventual clogging caused significant downtime to remove either by "rodding" or "steam cleaning", excessive wear to pumps and related equipment, and increased energy costs. As a result of this observation, they began to seek out a company that was capable of applying a "glass lining" to the interior surfaces of pipe and fittings.
The first company found was Ferro Enameling in the San Francisco area. At the time, cast iron pipe was still being produced and the lengths were shorter. Ferro Enameling was capable of processing 10 foot lengths. Later, as ductile iron pipe began to replace cast iron and the lengths began to increase, changes in the glass lining process were made to accommodate these longer lengths. At the same time, some concern developed over whether or not the heating process associated with the glass lining process would have any negative effect to the ductility of the iron. ACIPRA did extensive testing and determined that the process, if carefully controlled, actually improved the ductile properties of the iron. However, the temperature had to be controlled closely at approximately 1400 degrees F. That is the main reason why all of the larger glass lining producers have historically utilized electric furnaces. They provide much closer temperature range tolerances.
Glass lining has provided continuous beneficial service for nearly 40 years. The original glass lined systems were installed at wastewater treatment plants in Eugene, Oregon and Seattle, Washington (West Point Project) . Parts of these original systems continue to function satisfactorily today, except where expansions and design changes have prompted replacement. There is no other lining material that comes close to providing the kind of proven effectiveness and longevity as that of glass lined pipe.
What is Glass Lined Pipe
Glass lining is a form of porcelain enamel, much like the material that has been applied to tubs and sinks for many years. It is a combination of glass, water and clay applied to the base metal substrate at high temperature, typically in excess of 1350 degrees F. The glass is a combination of different types of borosilicate glass which is ground in a ball mill to a fine powder, approximately the consistency of flour or powdered sugar, which is sifted through 200 mesh screen. It is then mixed with water and a small amount of clay which acts as a binder. Very small amounts of other inorganic materials are added to control the viscosity and flow characteristics of the glass formulation. The water is simply a vehicle used to transport the glass material onto the surface of the pipe or fittings which have been properly prepared by blasting. The glass mixture is sprayed onto the interior surface of the pipe or fittings with special spray lances. Then the pipe or fittings are placed in drying ovens at a temperature of approximately 120-130 degrees F. where the moisture is removed. Once dry, the pipe and fittings are placed into specially designed furnaces and "fired" at approximately 1400 degrees F. The firing time will vary slightly, depending on the size and thickness of the iron and whether the base coat or cover coat is being applied. Firing times are typically in the vicinity of 1.25 to 1.50 hours for each of the coatings.
Vitco®'s 2 coat process is unique to the industry and is the key element responsible for the high level of quality associated with the Vitco® product. The base coat forms the initial bond with the base metal; the second coat or "cover coat" provides the non-stick and performance characteristics.
Significant Project Information
Over the years, various situations have occurred that provide significant evidence of the effectiveness of the glass lining in combating the build-up problems associated with the sludge and scum systems of the waste water and sewage treatment plants.
First, remember that the key target areas for usage of glass are areas where solids content of the media being transported are in the range of 3% or more. These are typically the areas where scum and sludges are collected and then transported through piping to the various stages of treatment. Also, areas where some abrasion is possible either within the sludge materials or after grit removal.
In 1994, we had conversation with individuals from a Denver Metro facility that had utilized glass lined pipe and fittings, but was still experiencing some build-up within the sludge systems in the digester areas. Investigation showed that the build-up was not in the glass lined areas, but instead in the various equipment in the system that was not glass lined, such as valves and supernatant tubes. We had done work on a very limited basis prior to this time with several valve manufacturers to develop a procedure for glass lining of plug valves, but had not pursued it to any great degree. Because of this inefficiency of the glass lined system, Denver agreed to allow us to attempt to successfully line a valve and install it as a test.
We worked closely with the Victaulic Company and were able to successfully develop the proper procedure for lining of the valve. We installed the first of the test valves in 1994 along with a new epoxy lined valve, which was what had previously been utilized in these systems. After approximately 1 year, the systems were opened to examine the valves. The epoxy lined valve had significant build-up and was basically inoperable. The glass lined valve was free from any interior build-up. As a result, Denver Metro replaced a large number of plug valves with new glass lined ones.
This application was significant because it showed the eventual lack of effectiveness of "organic" linings, versus the long term positive effects of the glass lining.
Other significant project data…. The information in the "40 years Experience" folder in the brochure relative to the Pigs Eye Plant in Minneapolis; Approximately 2 years ago, I visited the plant to discuss an upcoming addition to the plant. A comment was made by a relatively new operations foreman that "our system runs really well. Why do we need to go to the expense of providing glass lined material?" My comment to that individual was that he should check to see what the color of the inside of the piping was; that I was sure he would find it to be green. He did so, found out it was green glass, and the expansion will include a large quantity of glass lined pipe and fittings.
Deer Island in Boston, the infamous "Boston Harbor Project", is beginning to have some problems with build-up occurring in their sludge and scum systems, all of which were glass lined, EXCEPT the valves. We are currently having discussions with them and will be providing sample glass lined valves to install to provide proof of how a more complete glass lined system can eliminate their problem. Again, the significant information here is the limited effectiveness of the organic lined material versus that of glass lined.
Further proof of the problem on Deer Island is the fact that they have also found a few fittings to be clogged. Investigation has shown that these isolated fittings were not glass lined, but were instead lined with green epoxy, probably epoxy repair material furnished by us for touch-up of field fabricated pieces, and the epoxy has become totally ineffective at deterring the build-up.
Bottom line is this. Glass lining is slightly more expensive than organic lining materials; normally within a 15-20% premium. But, the performance benefits, and more importantly, the longevity associated with its use, easily justifies the added cost.