Hose Connector Failures

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Once again we are inviting comments on a recent safety concern and TGM’s efforts to remedy it.  A 1” air hose came loose from the connector fitting.  The hose whipped across the floor, narrowly missing two mechanics, before a quick thinking mechanic shut off the supply.

Our hoses were equipped with the fitting shown on the left.  After discussion with our supplier, we have chosen to replace this with the crimped sleeve connector shown on the right.  The connector is affixed with a computer operated machine.  The operator inputs the inside and outside diameters of the hose, the type of hose and the connector used.  The machine calculates and applies the correct pressure for a good crimp.

According to our supplier, most customers prefer the old double banded style connector because when a hose gets soft (usually at the ends by the connector) they can cut it and band it back together and save the cost of a new hose.

What do you think?  Are we being too cautious?  Is this a problem in your shop?  How do you handle it? Please click the link below and join the discussion.

Direct Current High Voltage (Potential) Testing

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Direct current high voltage testing can be divided into two categories: Proof testing and Controlled Over-Voltage testing.

Proof testing qualifies an insulation system to hold a specific voltage. By definition, it is a pass-or-fail evaluation – there is no diagnostic value. Acceptance proof testing is performed on new stator winding as part of in-process and final acceptance testing. Maintenance proof testing is performed on existing equipment, typically at 75% of the Acceptance test voltage. Although proof testing is pass/fail, the microampere readings for each individual phase should be measured and recorded, and gross variations should be noted and investigated further. An initial failure may be the fault of the test setup, as high resistance leakage to the atmosphere or to ground can occur. The quality of the insulation system should be questioned only if corrections to the test setup do not result in improved test results.

In Controlled Over-Voltage testing, the applied voltage is either “stepped-up” manually and incrementally, or “ramped-up” automatically and fluidly, over time. This provides a degree of diagnostic value since the measured current can be graphed, phase-by-phase, for comparative analysis. Controlled Over-Voltage testing affords the ability to salvage a winding that might otherwise fail in Proof testing. In plotting the measured current in real time, the operator may witness an exponential increase in current (indicating an impending insulation breakdown) and terminate the test.

DC stepped voltage and ramped voltage test results can be evaluated on a pass/fail basis, but important results can be obtained by a more thorough examination. The associated plotting might show evidence of a weakness. The higher the voltage level that presents the indication, the better the quality of the dielectric. Comparison phase-to-phase might show that one or more are comparatively high in resultant current.  Most importantly, routine testing and comparatives can provide insight into the degree of insulation aging, and help predict end of useful life.

All of these tests should be performed in accordance with IEEE Standard 95™-2002, IEEE Recommended Practice for Testing of AC Electric Machinery (2300 V and Above) With High Direct Current.

Exploding Sockets Revisited

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Recently, one of our sockets exploded while loosening a bolt using a HyTorc hydraulic wrench. No one was injured, but we take these incidents seriously, generating a “Near Miss” report and subsequent corrective action.

We discussed exploding sockets in a previous Safety Tip, which you can review in the May 8, 2012 post (see below). Since that post, we purchased TorcUp sockets for all our tool sets, and sprayed them yellow to make sure they were exclusively used with our HyTorc heads. One of these dedicated sockets broke under load. Please comment (below) on additional steps we can take for our corrective action.  We need your experience and expertise.

Additional information: The broken socket was less than a year old.  It was a 1” drive, 1 5/8” 12 point socket under an 8000 PSI load.  We chose TorcUP sockets as they were the middle of the road in pricing of the three vendors we reviewed (one was HyTorc).

All of us face similar safety concerns in our operations. If you would like one of your concerns discussed in this forum, please contact us via Mr. Turbine (click here) and we will start the conversation in our next newsletter. We will not share your contact info but you can also post anonymously.  Mr. Turbine will be happy to give an immediate response if you request it, but of course we must have your correct info.

Polarization Index (PI) Test

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A Polarization Index (PI) test is generally performed at the same voltage as the Insulation Resistance (IR) test.  Where the IR test is performed for a period of one minute, the PI test is performed over a period of ten minutes. This gives the absorption (polarization) current ample time to decay, and reveals a more detailed indication of the total leakage and conduction current. As such, PI is a good indication of winding contamination, moisture ingress (leakage currents), and/or bulk insulation damage (conduction currents).

Polarization Index testing is generally performed with an Insulation Resistance (IR) test set (commonly known as a Megger), immediately after performing the IR test. However, the test can also be performed utilizing a DC high potential (hipot) test set. The readings produced by the two instruments are different. A Megger commonly gives readings in ohms of resistance. A hipot registers the amount of current (typically in microamps (mA). One microamp is equal to 1 x 10-6 amps, or 0.000001 amps.

The Polarization Index is derived by the ratio between the one minute reading and the ten minute reading. Recommended minimum PI results for suitability for service (or implementation of high voltage testing) is widely accepted as 2:1 or greater. Any reading lower than this minimum value is a concern. The windings would be presumed to be wet, contaminated, and/or compromised in some fashion. Conversely, vintage windings (varnish cambric, asphalt mica, etc.) may produce an unusually high Polarization Index ratio.  The insulation may be void of binder content, thus making it dry and brittle.  According to IEEE standards, if the insulation resistance reading after the voltage has been applied for one minute is greater than 5,000 megohms the resulting polarization index may or may not be indicative of the true insulation condition and is therefore not recommended as a means of assessment.

Polarization Index testing should be performed in accordance with IEEE Standard 43-2000(R2006), IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery. A Megger brand model number BM25 (or its replacement or comparable) is recommended if a Megger is used. A High Voltage, Inc. PTS Series DC high potential test set is recommended if a hipot is used.

Proper Manual Lifting

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Back pain constitutes about 10% of occupational injuries and is the most common reason to take leave from work.  Each year about $50 billion is spent on treatment in The U.S. alone, making it the third most expensive condition after heart disease and cancer. With this in mind, an ounce of prevention is worth a pound of cure (pun intended). Before lifting an object of unknown weight, perform several trial lifts using gradually increasing effort.  Do not attempt to lift an object that you cannot confidently handle. Always identify the path you will be taking with the load and clear away all obstacles. Use proper gear for every lift. Wear shoes with good traction and solid gripping gloves which will help you to hold the object for a longer period of time.

Avoid standing too far from the load as it might not provide you the needed grip to hold the object properly. Align yourself properly over the load with your feet and shoulders wide apart. This will give you the exact balance needed to hold the load while lifting it. Never bend at the waist and lift an object with your back. Keep your upper body straight and parallel with your lower legs. Grab the item and push up with your legs, not with your back. Never rotate or twist your body while lifting. Keep your head up when handling the load. Look ahead, not down at the load once it has been held securely. Make sure you lift with a slow, steady force. This will help you avoid muscle strains from having to counter an unbalanced load. Take smooth and small strides to avoid muscle strain from overcompensating for shifting loads. For heavier loads, try lifting with your full breath, and tighten your abdominal muscles for added support. For long lifts, such as from floor to shoulder height, consider resting the load mid-way on a table or bench to change your grip on it.  Always use a lifting belt or back brace if preforming multiple lifts. Don’t lift or handle more than you can easily manage. There’s a difference between what people can lift and what they can safely lift. If at all possible, get help.  Lift with a buddy or use a mechanical lifting device such as a crane, chain fall or a jack.

Insulation Resistance (IR) Test

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The Insulation Resistance Test measures the integrity of the generator’s winding insulation, and therefore the likelihood of developing a ground.  A test voltage is applied to the generator and the current flow required to maintain that voltage is measured over a period of time (typically one minute).  In simplest terms, the less current flow, the higher the resistance value, and the better the insulation.

An IR test should be performed immediately following any type of event that is suspected of over-stressing an insulation system, prior to the generator being placed back into service. This is the first test that should be performed. The results will indicate the ability of the insulation system to withstand  any more searching and/or strenuous testing. The IR test also measures the effect of contamination from water, oil, carbon, and other such undesirables. If a separate high voltage proof test is performed, an IR test should be performed both before and after the proof test. This in order to assure that the proof test itself has not compromised the insulation.

The Insulation Resistance test must be performed by a well trained and experienced technician.  Incorrect procedures can materially affect the results. The test should be performed to IEEE Standard 43-2000 (R2006), using a late model Megger brand machine such as Model MIT1025, or comparable.  It is best practice to test at the main and neutral leads of the stator, as close to the windings as possible.  Stator slot RTD’s should be disconnected from the terminal board and grounded. Surge capacitors should be disconnected.  The water or oil should be drained and completely evacuated from liquid inner-cooled windings, typically by vacuum-processing. Stator windings should be tested one phase at a time, with the other two phases grounded. In this manner, the windings are stressed both phase-to-ground and phase-to-phase.

The results should be interpreted by an experienced technician. Your final report should reflect that environmental conditions and even the age and configuration of the machine were taken into consideration.

If you have any questions concerning the application of this test or the interpretation of the results, please contact Mr. Turbine.

Starting Over

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We’re embarrassed. We had our first recordable accident after 909 days (over
500,000 hours). Just when everything was going so right. We had the toolbax safety meeting at start of shift to discuss the day’s hazards. We had the Job Safety Analysis for the task to be performed. We had top management buy-in and a dedicated and experienced Safety Director conducting random on-site inspections. But a mechanic was not wearing gloves when he knew he should have been, and he cut his finger. He may not have a scar on his finger from the incident, but the permanent scar on his soul gives evidence of the depth of the safety culture at TGM.

And we still had an accident. Take heed from our mistake:

Hands are hurt more often than any other part of the body. Your hands are your wage-earners. As talented as your hands are, they can’t think; they are your servants, and it is up to you to think and keep them out of trouble.

Be sure you wear the right kind of gloves for the particular kind of work you are doing. When you wear gloves, you aren’t trusting to luck and you’re not taking unnecessary chances. Wear gloves when you are doing a job that needs them, but not around moving machinery. Time spent in preparing your hands for the job will not only save trouble for you but will probably save time in doing the job.  Refer to your SDS (MSDS) sheets for gloves required for use with certain chemicals.

What is a Confined Space?

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A confined space does not necessarily mean a small, enclosed space. It could be rather large, such as a ship’s hold, a fuel tank, or a pit.

One of the first defining features of a confined space is it’s large enough to allow an employee to enter and perform work. The second defining feature is it has limited means of entry or exit. Entry may be obtained through small or large openings and usually there is only one way in and out. The third defining feature is that confined spaces are not used for continuous or routine work.

All confined spaces are categorized into two main groups: non-permit and permit-required. Permit-required confined spaces must have signs posted outside stating that entry requires a permit. In general, these spaces contain serious health and safety threats including:

  • Oxygen-deficient atmospheres
  • Flammable atmospheres
  • Toxic atmospheres
  • Mechanical or physical hazards
  • Loose materials that can engulf or smother

Although a confined space is obviously dangerous, the type of danger is often hidden. For example, a confined space with sufficient oxygen might become an oxygen-deficient space once a worker begins welding or performing other tasks.

These are some of the reasons confined spaces are hazardous:

  • Lack of adequate ventilation can cause the atmosphere to become life threatening because of harmful gases.
  • The oxygen content of the air can drop below the level required for human life.
  • Sometimes a confined space is deliberately filled with nitrogen as a fire prevention technique. Nitrogen cannot sustain human life, so you must use respiratory protection.
  • Many gases are explosive and can be set off by a spark.
  • Even dust is an explosion hazard in a confined space. Finely-ground materials such as grain, fibers and plastics can explode upon ignition.
  • Confined spaces often have physical hazards, such as moving equipment and machinery.
  • Tanks and other enclosed confined spaces can suddenly be filled with materials unless the flow process for filling it is controlled.

Before entering any confined space, you must test the atmosphere to determine if any harmful gases are present. There must also be radio contact with an attendant outside the confined space and a rescue team at the ready in case of an emergency.

Don’t Kill Your Turbine on Startup

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Your lube oil temperature needs to be lower at startup and shutdown than at full
speed.

Your turbine’s rotor does not actually ride on the surfaces of its bearings. It rides on a thin film of oil between the rotor and the bearing. At high turbine speeds the rotor hydroplanes across the oil, eliminating contact with the Babbit of the bearing. The heat generated by the turbine decreases the viscosity of the oil and increases its “slipperiness”, which is important at high speeds. As the rotor slows, the oil needs to be more viscous to repel the force towards the bearing.

Failure to lower the lube oil temperature (and therefore increase viscosity) can result in light bearing wipes or smearing.  These conditions would occur during turning gear operation, unit startup and unit coast down during shutdown.  The ideal lube oil temperature at these lower speeds is 90 degrees F.  Of course, oil temperature can also be too cold on startup, similar to trying to start your car on a cold winter day. Operational personnel are ultimately responsible for maintaining this lower lube oil temperature by regulating water through the lube oil coolers.

Maintaining lube oil cooler cleanliness is also very important. The tubes must be clean for efficient transfer of heat. The bundles should be cleaned every two (2) years.  Lube oil coolers are the single most common area for contaminants to hide. These contaminants can also lead to bearing failures, as discussed in an earlier Turbine Tip.

Prevent Crushed Fingers

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Each year, workers suffer approximately 125,000 injuries that occur when body parts get caught between two objects or entangled with machinery. These hazards are referred to as “pinch points”. If you have ever slammed your finger in a door, you can appreciate the pain associated with this common type of caught/crush injury. The physical forces applied to a body part caught in a pinch point can vary and cause injuries ranging from bruises and cuts to amputated body parts and even death.

To prevent these injuries, look for possible pinch points before you start a task. Take the time to plan out your actions and decide on the necessary steps to work safely. Give your work your full attention. Don’t joke around, daydream, or try to multi-task on the job – most accidents occur when workers are distracted. Read and follow warning signs posted on equipment. If you value all that your hands can do, THINK before you put them in a hazardous spot.

Also, dress appropriately for work with pants and sleeves that are not too long or too loose. Shirts should be fitted or tucked in. Do not wear any kind of jewelry. Tie back long hair and tuck braids and ponytails behind you or into your clothing. Wear the appropriate, well-fitting gloves for your job.

Machinery can pose a hazard with moving parts, conveyors, rollers, and rotating shafts; these are only a few of the vast number of hazards. Never reach into a moving machine. Properly maintain and always use the machine and tool guards provided with your equipment. Don’t reach around, under, or through a guard and always report missing or broken barriers to your supervisor. These guards act as a barrier between the moving parts and your body. Turn equipment off and use lockout/tagout procedures before adjusting, clearing a jam, repairing, or servicing a machine.

Vehicles, powered doors, and forklifts can pose a crush hazard unless they have been blocked or tagged out. Never place your body under or between powered equipment unless it is de-energized. Doors, file drawers, and heavy crates can pinch fingers and toes. Take care where you place your fingers. Test the weight before lifting, carrying, and placing boxes; an awkward or heavy load can slip and pinch your hands or feet. Get help or use tools to move large and/or heavy items.

Take the time to learn about the caught/crush hazards in your workplace so you don’t learn about the consequences first hand (no pun intended).