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O-ring Evolution

December 15, 2011

O-ring Evolution


If an O-ring equipped probe of an injection elbow were to break-off or otherwise fail, can we replace it with a standard probe?

[dt_divider style=”thin”]A:The absolute best choice is to replace the damaged probe with an identical probe. Novinium would be happy to provide these probes to you with only a modest markup. If the Novinium masters of reliability are in town, just give them a call as they likely will have spares on their truck. Your question is probably targeting the case when there are none of these O-ring equipped probes nearby and you desire to put the cable back in service. To answer that question it is useful to explain how the O-ring-equipped probe evolved.In the illustration nearby, I point at a fully evolved O-ring on a probe pin. In this 2011 incarnation the O-ring is seated in a composite sleeve molded into the elbow throat. The very first injection elbows were invented by my colleague, Glen Bertini and his associate at Dow Corning, Dan Meyer, about 25 years ago. The very first injection elbow, used from 1987 to 1989, was a standard elbow with a capacitive test point. Bertini and Meyer drilled and taped a hole through the capacitive test point and screwed an insulating nylon cap into the hole. The elbow worked flawlessly, but was properly considered unreliable for long term operation and hence the elbow was treated as a tool. After the injection was complete the modified elbow was swapped for an unmodified elbow of the same size. There was no O-ring in either elbow. Cablecure® 2-2614 fluid, which was (and remains) predominately phenylmethyldimethoxysilane (PMDMS) and has a flash point of about 66°C flooded the bushing on 100% of the applications. There were no adverse consequences observed.[dt_fancy_image type=”image” image=”” style=”2″ width=”600″ padding=”10″ margin_top=”0″ margin_bottom=”0″ margin_left=”0″ margin_right=”0″ align=”center” animation=”none”]The history of the O-ring spans over two decades!The next improvement in the injection elbow was the introduction of a dedicated interference fit injection port. The collaboration between Bertini and Meyer of Dow Corning and Alan Borgstrom of Elastimold yielded two U.S. patents, 4,946,393 and 5,082,449 in 1989 and 1990. This advancement meant that the injection elbow could be left in place indefinitely … only the injection cap had to be swapped. There still was no O-ring, hundreds of thousands of feet of cable were injected, and there was precisely one problem. Sometime in late 1989 a bushing failed because the CableCURE 2-2614 fluid had dissolved a plastic component within the bushing. Elastimold and Dow Corning immediately tested the fluid and bushing component compatibility and found no issues that detracted from the elbow-bushing compliance to IEEE 386™.

It turns out the single bushing that failed was an anomaly—not a large production bushing. None-the-less, Dow Corning and Elastimold decided that even though incompatible bushings would be a rarity, it would be prudent to add a seal to the system to minimize the probability of adverse fluid interactions within the bushing.  An O-ring was added to the probe in about 1991.  The rubber O-ring was not seated in a rigid collar and hence a small deflection of the probe pin would allow a leak. This problem was minor, however, because when the elbow was seated on the bushing it was held in a perfectly centered position.

Two years later in about 1993, UTILX® Corporation, after licensing Cablecure technology from Dow Corning, unveiled another Bertini innovation (U.S. Patent 5,372,841), which was called Cablecure XL fluid. While XL fluid brought significant dielectric performance gains, it suffered from a much lower flash point and it wasn’t too long before the imperfection of the O-ring seal lead to fires when a fluid-filled elbow was switched. Over the course of the next decade, the seal was changed several times to improve its robustness.

Novinium fluids are not flammable. See my November 2, 2011 post “Fluid Flammability” for more on this subject. If you are using a flammable fluid from another supplier, I would highly recommend using only O-ring probes. With Novinium fluids the risk is minimal. There is a low risk that fluid will get into the bushing after the injection has been completed, and that risk decreases as time-since-injection advances. There is an even lower risk that Novinium fluids in the bushing will create any safety or reliability issues.

In 2012 Novinium and our component manufacturing partner will be introducing an entirely new injection device suitable for both unsustained pressure rejuvenation (UPR) and sustained pressure rejuvenation (SPR).  It will be inherently leak-free. When the new injection device becomes commercially available, switch to it and your question will become moot.