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SpringSeal® Improves Pipe Gasket Performance
CASE STUDY:
SpringSeal® pipe gasket
OBJECTIVE:
To produce a pipe gasket with a higher level of performance while using less material
DESIGNER:
SpringSeal® Inc.
MATERIALS USED:
Santoprene™ brand TPVs
COLOR:
Black
MANUFACTURING PROCESS:
Multi-layer extrusion
PROBLEM
For many years, gaskets and seals for the polyethylene and PVC pipe industries were traditionally manufactured using thermoset rubber. In the mid-1990s, Mark Knapp, founder and president of SpringSeal® Inc., had the idea to develop dual hardness gaskets in order to improve sealing performance. While dual durometer technology was available in the rubber industry, it was deemed very specialized and expensive. If a dual durometer gasket were to be successful, the design and material selection would be crucial.
SOLUTION
Having developed a design for a dual durometer gasket, SpringSeal of Streesboro, Ohio initially selected an SEBS-based thermoplastic elastomer (TPE) for product trials. However, due to problems with the heat and UV resistance of the material, the gasket failed in field applications.
As an alternative, a local manufacturer recommended using a thermoplastic vulcanizate (TPV), a higher performance TPE based on EPDM rubber and polypropylene. This material had not been widely considered for pipe gaskets primarily because it was not regarded as being price competitive compared to thermoset rubber.
Using a TPV was to prove critical as it allowed a gasket design that simply was not possible with thermoset rubber. Importantly, the design of the new dual durometer gasket used significantly less material, overcoming the differential in cost between the TPV and thermoset rubber. After pressure testing the pipe to compare a thermoset rubber gasket with a TPV gasket, SpringSeal discovered that dual durometer TPV gaskets improved the sealing performance by increasing the hoop strength of the pipe.
SpringSeal was so encouraged by the success of the early tests that it proceeded to further develop these initial design concepts. A new approach in gasket design and manufacturing had begun.
“We needed to find a company that could provide the right level of support – a company we could rely on to help us successfully develop these new gaskets, enabling us to break into the large diameter pipe seal market. Obviously, the company would also need to provide TPV materials that would meet specific performance criteria,” said Knapp. “We selected ExxonMobil Chemical’s team for Santoprene™ TPVs because of its unparalleled expertise and experience in the elastomer industry.”
ExxonMobil was very involved in advising SpringSeal during the successful development and launch of its new products, from material recommendations to sales support involving meetings with major pipe OEMs.
The minimum performance of SpringSeal’s products is dictated by standards set by ASTM, CSA and other similar organizations. The company needed a material that could not only meet these standards but surpass the performance of products manufactured using thermoset rubber. Santoprene TPV met the requirements and ExxonMobil provided data from test studies taken over a 14-year period which demonstrated that the specialty elastomer would last longer and outperform the current thermoset rubber materials.
Material recommendations were in fact critical to the application with three different grades of Santoprene TPV being used to perform specific functions. One grade was for the sealing portion, another for the low-coefficient-of-friction (COF) film layer and the final grade for the high modulus reinforcement portion. To assist in SpringSeal’s product design, ExxonMobil utilized sophisticated 3-D finite element analysis (FEA) modelling to simulate stretching the gasket on the pipe, assembling the pipe joint (thus compressing the gasket), and finally fully pressurizing and stress testing the joint. In each case, a high density polyethylene (HDPE) pipe was modelled as a flexible material to accurately predict the sealing characteristics of the system. FEA determined the pipe insertion forces, seal contact pressure and appropriate material locations for a variety of seal designs. Using this data, the seals were then manufactured to specification using tri-extrusion processing.
ExxonMobil undertook in-house prototyping of tools for the complex tri-extrusion designs. Standard and proprietary tests, such as assembly force and joint tightness were also performed in-house, as well as at third party test laboratories. This “proof of concept” testing validated what the FEA model predicted – that the pipe joint could be assembled completely dry with no added external lubricant. Furthermore, the seal remained in its designed location on the pipe, eliminating the possibility of gasket roll-off, a common problem with thermoset rubber gaskets.
Application support was provided to help SpringSeal understand the various regional specifications and standards required for product selection and compliance. ExxonMobil provided processing support to optimize the critical extrusion variables associated with gasket performance and assisted with the recommendations for extruding and downstream equipment.
Finally, a cooperative development agreement was put in place at the beginning of the project. This has led to several patents between the two companies in various world areas.
Manufacturing today takes place at the company’s main plant in Garrettsville, Ohio and at a processor based in St. Louis, Missouri, using methods unavailable with traditional thermoset rubber. The thermoplastic gaskets are manufactured using high speed co- and tri-extrusion technologies and are fused together using a proprietary welding system. The gaskets are processed as a plastic at a lower temperature than the thermoset gaskets they replace. This more energy efficient process, along with the ability to recycle Santoprene TPV, is becoming an increasingly important benefit as it reduces costs and waste.
“It has been a great experience. ExxonMobil has assisted SpringSeal in all aspects of developing these new gaskets. It has taken many years to fine tune the products and bring them to market. Having ExxonMobil’s support in so many different areas has been vital to our success,” said Knapp.
SpringSeal quickly established a reputation for manufacturing highly engineered, price competitive products which offer many performance advantages compared with conventional pipe gaskets. The company is producing systems using multi-durometer Santoprene TPVs to provide a higher level of performance than conventional gaskets.
It claims to be the only company that offers dry assembly gasket systems that do not require manual application of lubricants for effective assembly. Not only does this reduce joint failures caused by improperly lubricated gaskets, but it also speeds installation time and saves money for pipe installers.
RESULTS
Prinsco Inc. of Prinsburg, Minnesota, an industry leader in the development and manufacture of corrugated polyethylene drainage products, has benefited from SpringSeal’s gaskets for a number of years. It has been using the high performance, multi-durometer gaskets in its established Goldlfo WT® product range. Comprised of an HDPE pipe with an integral bell and spigot joint, Goldflo WT® products meet the requirements of ASTM D 3212 which requires a joint integrity internal pressure rating of 10.8psi for HDPE sewer pipe.
“Previous gaskets were big, bulky and heavy because of the sealing area needed to meet these ASTM pressure rating requirements,” said Joe Hawkins, director of quality, Prinsco Inc. “The major improvements of SpringSeal’s dual durometer gaskets are an effective, smaller sealing point due to the design of the top layer of the gasket, less resistance in joint assembly because of the slick nature of the sealing material and the relatively stiffer hollow bottom layer which anchors the gasket in place.”
The biggest advantage, in addition to sealing performance, is the reliability of the gasket in the field, which is particularly important in the growing ‘water-tight’ market.
“Conventional gaskets require a large amount of lubricant due to their size and the material used,” said Hawkins. “This can cause occasional gasket roll-off. Even without lubrication, SpringSeal gaskets are designed to remain in the gasket seat and perform as expected. However, as some of the joints are extremely tight, lubrication is still recommended for the best performance. It all comes down to quality installation which is essential to our success.”
