Q We recently installed a new steam pressure reducing station in an existing 6-m. 150-lb steam line. After reinsulation of the pipe with foil-jacketed, 2-in.-thick fiber glass, electrical arcing started between the new insulation foil jacket and the steel strainer [ILLUSTRATION FOR FIGURE OMITTED]. The spark jumps a gap up 1/2 in. To date, we have been unable to find a logical reason for the arcing. Is it possible that the steam flow through the pipe is generating a charge that builds up within the insulation to a point where it discharges to ground through the steel pipe? Should this be a concern to computer terminals and electronic boiler controls? - J.F.H.
A The sparking that is occurring on J.F.H.'s newly installed steam pressure reducing station (from the insulation foil jacket to the steel strainer) may be due to a strong electromagnetic field. This could be from a nearby broadcast transmitter, high-frequency induction heater, x-ray machine, electrostatic paint line, microwave process, or even a malfunctioning neon, fluorescent, or HID lamp. Whatever the original source of this arcing, it will make its presence known on adjacent sensitive devices, such as electronic boiler controls and computer terminals, via inductive coupling to any nearby communication wires. The best method to eliminate this undesirable electric effect is to bond the insulation outer jacket foil to the underlying pipe at frequent intervals as well as across any jacket breaks, such as those indicated at the bolted flange pipe joints shown in the figure. Also, J.F.H. should verify that the entire pipe is bonded to the facility's ground grid/structural steel at many points. This will eliminate the voltage buildup between the insulation's outer jacket foil and the pipe. - F.M.P.
A It is highly improbable that the 6-in. steel steam piping system in this problem is not earth-grounded. Therefore, because electricity flows from a higher potential to a lower potential (ground), the spark seen jumping from the metal jacket to the pipe is doing just that: Flowing from the pipe covering metal to the ground. The fiber glass insulating material is an electrical insulator and a heat-loss barrier.
J.F.H.'s sketch shows the metal jacketing to be electrically isolated from the other jacket installations adjacent to the strainer. This condition is forming an electrostatic accumulation system, with the isolated jacket on the strainer acting as a capacitor. This sheet of metal may well be 5 sq ft or more in area. The system does collect enough potential difference to form the spark mentioned. Fortunately, this is a high-voltage, low-amperage discharge with little possibility of personal injury. But, it will be enough to startle a beneficiary of the bolt. Obviously, this is a problem, and must be corrected by connecting the metal jacket over the insulation to the rest of the jacketing or directly to the steam pipe itself.
Steam flow in the piping is not a concern as a static generator. What may happen is that low humidity conditions contribute to static conditions, leading to accumulation of a charge on the isolated jacket, thus to discharge; or charged clouds in the atmosphere locally will create a difference in potential on the jacket with an arc to ground. There may also be static generation in the local plant processes, which are not noted in the question.
If this phenomenon were injurious to J.F.H.'s electronic boiler controls or computer terminals, it would have already happened. This is not to say that there is no potential for harm to the computer systems, but effectively grounding all portions of the metal pipe jacketing will certainly reduce the probability to a minimum. - B.B.B.
A I've worked around boilers and steam-curing processes for several years. J.F.H.'s problem is not unique. In the figure, J.F.H. indicated there were two steam leaks. The steam leaks cause static charges to build up in the area around the leaks. Once the charge is sufficient, it arcs or discharges to the nearest conductor, which happens to be the foil jacket on the fiber glass insulation. Any time there is a steam leak, J.F.H. should have it repaired as soon as possible. This not only saves a lot of energy from being wasted but also avoids the problem J.F.H. encountered. I've never seen a static problem from a steam leak damage electronic boiler controls yet. Usually, the leaks are in the steam lines and not in the boiler itself. Also, the boiler controls are usually placed in a suitable enclosure to protect them from outside interference. - J.M.H
A An arc jumping a 1/2-in. gap must be of several thousand volts, even in the presumably high humidity area near a pressure reducing station. Any static electric voltage, generated by a flow of steam, would be "grounded" by the steel pipe itself. The source of the electricity must be external to the steam system. I assume J.F.H. has already looked for possible contact with adjacent wiring. I also must assume the insulation jacket is not "broken" at the flanged joints shown in the drawing. The source of electricity must be further away from the point of the arc than J.F.H. has sought.
If the insulation jacket is broken, (sections of the jacket isolated from each other) J.F.H. should insulate all flanges, valve bodies up to the stem packing box, strainers, and all fittings. If he does that, he will save an additional 5% to 15% of his heat energy (and possibly find the electricity contact along the way).
This voltage, if allowed to continue, will undoubtably affect his computer terminals and boiler controls, which should be no higher than 120V and may not be designed to resist the higher voltage indicated by the arc.
Attaching a recording voltmeter across the gap will indicate whether the voltage builds up "slowly" or is continuous and may indicate the source of his problem. If not already purposely grounded, J.F.H. ought to bond all portions of the jacket ground. This may cause fuses or breakers to open, again indicating a source of his problem. In any event, grounding must be done immediately to protect personnel who may come in contact with the strainer when "blowing it down" (which ought to be done periodically). - L.A.B.