Don’t Kill Your Turbine on Startup

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

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

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).

When a Backup Isn’t a Backup

The International Association of Engineering Insurers found that the highest frequency of steam turbine failures worldwide is due to loss of oil pressure. Most of these failures are caused by an unreliable backup system to maintain oil pressure to the bearings should the primary AC-driven lube oil pumps fail. These AC motors are powered by either the turbine’s output or the grid, and will fail if the turbine or generator trips, or if there is an external outage.

Modern turbines have backup powered DC oil pumps mounted on the oil tank which are triggered by a pressure switch in the event of a loss in oil pressure. It is very important to conduct tests with the AC and DC oil pumps during scheduled maintenance inspections to ensure that the DC pump engages as required. Such tests can be referred to as cascade pump pressure inspections. These tests will confirm the pressures when the DC oil pump will engage after the AC oil pump is actually turned off. Backup batteries should also be verified. These tests should be performed on a regular basis when the unit is down and mandatory tests should be performed before the unit is placed in operation after an overhaul.

Older turbines can use steam-driven pumps as backup. On these designs, a pressure regulator will sense the drop in bearing oil pressure and turn on the steam supply to the blade wheel of the pump. While these pumps are usually very reliable, they still must be manually tested on a regular basis and after an overhaul. Care must be taken to not overspeed the pump or it will cause internal component damage and may even completely destroy the pump.

Some older turbines use gravity lube oil tanks.  These tanks are mounted above the unit on stands and are controlled by a check valve type of arrangement.  There are no pumps involved; gravity provides the bearings with sufficient lubrication in an emergency situation. While less complicated than DC or steam powered backups, their operation must still be routinely checked.

Bottom line, a backup is not a backup unless it is reliable. And it can only be reliable if it is tested.

Surviving Winter Weather

Winter is definitely here across the U.S. Here are some points on surviving the cold that you can tailor to the particular circumstances of your workplace:

Winter Driving

* Keep in mind that while black ice can form anywhere the temperature drops below zero, the condition is more prevalent in some parts of the country than others. Find out about the weather and road hazard patterns in the area you will be traveling.

* Prepare any of your mechanics and subcontractors driving for the possibility of being stranded in bad weather. Remind everyone to carry winter clothing, including boots, gloves, and hats in their vehicles.

* If your mechanics don’t live in the snowbelt, winter driving hazards can be a big concern. You need to emphasize to them the special driving hazards and risks associated with longer hours of darkness and weather such as rainstorms.

Winter Hazards in the Workplace

But it’s not just the road that’s slippery in winter. Loading docks, stairways, equipment yards, parking lots, and other areas of the plant or facility can also become icy.

Adapt safety meetings to the particular fall hazards that are common to your work crew. Do they have to get in and out of vehicles in icy weather? Must they walk along loading ramps to do their jobs? Steps, stairs, ramps, and ladders are all more dangerous in wet or icy weather, especially during the night shift. Remember that moist skin can stick to freezing surfaces. Check your work-site for areas that could be a particular hazard in the cold weather and discuss them in your morning toolbox meetings.

Effects of Darkness

The winter solstice around December 22 is the darkest time of the year. Outdoor workers are likely to be affected most by the increased darkness. But anyone who arrives or departs from work in the dark also needs reminding about special safety concerns, such as increased risk of slips, trips and falls, and personal security risks.

Be cautious using outdoor lighting around utility or construction jobs where flammable gas may accumulate.  It is importance to use light devices designed for decreased sparking.

The long dark winter can create or enhance symptoms of depression in employees, including lethargy, irritability, and forgetfulness. The depression can lead to increased use of alcohol and/or difficulty in relationships, which can further decrease employee productivity and awareness.

Early hours can also lead to dangerous fatigue; talk to the crew about getting enough sleep and coping safely with early shifts.

Make your safety talks address the particular risks cold weather creates on the specific tasks workers perform.

Cold Stress

Workers who are exposed to extreme cold or work in cold environments may be at risk of cold stress. Extreme cold weather is a dangerous situation that can bring on health emergencies in susceptible people, such as those without shelter, outdoor workers, and those who work in an area that is poorly insulated or without heat. What constitutes cold stress and its effects can vary across different areas of the country. In regions relatively unaccustomed to winter weather, near freezing temperatures are considered factors for “cold stress.”

Prolonged exposure to cold, even at temperatures well above freezing, can result in abnormally low body temperature (hypothermia). A body temperature that is too low affects the brain, making the victim unable to think clearly or move well. This makes hypothermia particularly dangerous because a person may not know it is happening and will not be able to do anything about it.

Cold stress is accelerated if a body part is exposed to water. Water conducts heat away from the body faster than air. Local cooling can shut down circulation in the capillaries under the skin, which can result in permanent damage such as chilblains, trench foot or frostbite. These effects can be experienced at temperatures as high as 60 degrees F.

Whenever temperatures drop decidedly below normal and as wind speed increases, heat can more rapidly leave your body. Wear appropriate clothing and protect sensitive areas such as hands, feet and face. Several layers of loose clothing will provide better insulation, especially if you alternate periods of exertion and rest. Wear a cap or rag under your hard hat. Stay in heated locations during work breaks, and limit outside exposure on extremely cold days.

Weather-related conditions may lead to serious health problems. So be prepared to cover up and stay warm.

High Bearing Loading

Past Turbine Tips have covered the main reasons for bearings to wipe: 1) Insufficient lube oil supply, 2) Low lube oil pressure, and 3) Water in the lube oil. Every once in a while a fourth cause appears: High bearing loading.

Proper bearing loading is calculated by the elevations of the bearings, component weights and shaft alignments (bending moments, lateral, torsional). The OEM calculates the elevations and coupling alignments during the design process, based on the catenary curve (or sag chart). Calculations ofbearing loadings and alignment are usually accurate based on the design engineers’ mathematical calculations and computer model for the rotor’s geometry, speed, weight, and bearing design.

The Catenary Curve

Most of the time, high bearing loading is caused by misalignment of the turbine power train from the original design. That is, some force has moved the components from their original alignments. The source of the bearing failure can be eliminated by carefully measuring and re-aligning to the original specifications. But we have seen examples where the original calculations either were not accurate orover years of operation the bearing pedestals had moved.

Recalculating bearing loading is an arduous and potentially expensive process, so all other contributing factors should be eliminated before attempting this course. If necessary, TGM can perform the recalculation and re-alignment without the participation of the OEM. On three bearing units, it is not uncommon to utilize a dynamometer to check bearing loading during alignment and their adjustments.

An Attitude of Safety

Have you ever noticed that people who are successful in life, or are just happy, tend to have a positive attitude? And so it is with safety. Look at it this way–safety rules and procedures are written to protect you from harm. They are not written to make your work life more uncomfortable or inconvenient. After all, safety equipment and training costs your employer additional upfront money.

If you cooperate in safety matters, not only is there a lesser likelihood of you getting hurt, but you will not be doing battle with the people enforcing the safety rules. In addition, you should feel more confident on the job knowing you have a better chance of making it thorough the day without injury. Less fear of injury and the thought of no one on your back has to brighten your day!

We are not perfect. Even the best of us can forget or make errors in judgment. To maximize our safety efforts, we must look out for one another. If someone tells you that you are not working in a safe manner, do not become angry or defensive. They are just looking out for your well-being. If you did not know you were doing something wrong, be thankful your errors were noted before someone got hurt. If you simply forgot or got a little careless, be grateful that someone cares enough to get you back on track. If you see someone doing something unsafe, speak up, but do so diplomatically. Treat others just as you would like to be treated in the same situation.

Remember, attitude affects behavior. If you have a positive attitude, odds are you will exhibit safe behavior. A negative attitude toward safety will only cause conflict, stress and, ultimately, an accident.

This month, TGM celebrates over two calendar years without an OSHA-recordable accident. Please join us in our goal of an accident-free year.

Prevent Bearing Failures

TGM believes that forced outages can be avoided with proper maintenance and periodic assessments performed during a short outage. Unfortunately, we see all too many examples of too few inspections and too little maintenance.

Here’s an example from one of our recent projects. The picture below is a gearbox bearing on a line shaft gearbox that had not been inspected for several years. One bearing is on one side of the bull gear and there is another just like it on the other side. As you can see, the bearing is fully wiped – it is a wonder it is still functioning. If the bearing had failed, the entire gear set would have collapsed, necessitating a compete replacement. The gear set is expensive but the real loss would be the substantial downtime for the plant as a new gear set is manufactured.

An investigation of the cause revealed very dirty oil and water in the oil but the root cause was alignment issues. We found improper spacing between the drive shaft couplings which put stress on this combination thrust and radial bearing. The increased heat from this stress led to oil degradation, made worse by the water contamination. Consequently, poor lubrication caused the bearing to wipe. Alignment issues can also be detected through vibration changes or abnormal wear patterns on the complete set of bearings. These “running assessments” are crucial to predicting problems before they cause serious damage.

It is relatively inexpensive to inspect the bearings every two years and damaged bearings can usually be replaced during the outage window. However, an incident such as overheating, abnormal vibration, or water ingress is evidence of potentially serious problems and must be addressed immediately. Any extra effort required to keep the oil clean and relatively water-free will also signal the need for an early inspection/overhaul. (See also our past Turbine Tips for maintaining the Lube Oil system and also note that re-Babbitted bearings should be UT inspected for proper bonding of the Babbitt to the shell.)

Big Problem = Hot! Hot! Hot!

The current heat wave engulfing the U.S presents big problems for all our employees. Particularly at risk are those who work in high air temperatures and/or high humidity, near radiant heat sources, and/or engage in strenuous physical activities. In other words, conditions typically found on the turbine deck.

When a person works in a hot environment, the body must get rid of excess heat to maintain a stable internal temperature. We do this mainly through circulating blood to the skin and through sweating.  Cooling the body becomes more difficult when the air temperature is close to or warmer than normal body temperature. Blood circulated to the skin cannot lose its heat and sweating becomes the main way the body cools off. But sweating is ineffective in high humidity because the sweat can’t evaporate. In extremely low humidity, sweat may instantly evaporate from the skin, disguising the need to replace that vital water.

If the body cannot get rid of excess heat, the core temperature rises and the heart rate increases. Loss of salts (electrolytes) can impair muscle and brain function. Injury can also result from sweaty palms, fogged-up safety glasses, dizziness, loss of concentration, and burns from hot surfaces or steam.

Excessive heat can cause a range of illnesses, from heat rash and heat cramps to heat exhaustion and heat stroke. Initially, the person begins to lose concentration and has difficulty focusing on a task. He may become irritable or sick, and often loses the desire to drink. The next stage is most often dizziness or even fainting. Heat stroke can result in death and requires immediate medical attention.

The best way to prevent heat-related illness is to make the work environment cooler by staying in the shade and employing fans and adequate ventilation, or even air conditioning. If it is still hot, employ safe work practices such as enforced work/rest cycles, water breaks, and providing an opportunity for workers to build up a level of tolerance to working in the heat. Be sure to include these prevention steps in worksite training and plans. Remember to refrain from alcohol intake the night prior and coffee during the shift. Alcohol, coffee and some prescription medications are diuretics which increase the rate of fluid loss. If the temperature is soaring and you are not urinating, you are not getting enough fluids.

It’s important to know and look out for the symptoms of heat-related illness in yourself and others. Plan for an emergency and know what to do – acting quickly can save lives!

Beware Exploding Sockets

Beware Exploding Sockets

Hytorc® bolting heads have long been regarded as a safer alternative to hammering on a striking wrench to remove stubborn case bolts.  But even impact sockets can shatter under extreme Hytorc® pressures, sending shrapnel rocketing across the turbine deck.  These explosive failures can cause serious injury or even death.

These failures can be reduced, but not eliminated, by using the correct socket. Impact rated sockets must be used at a minimum.    Old or worn sockets are of particular concern. Ill-fitting sockets do not fit tight on bolt heads.  This changes the stress points from the corners to the flats of the sockets and causes them to fail.  Best practice is to inspect sockets regularly and color code or otherwise identify them for this use. Another check for reliability would be to have the sockets inspected for potential indications of stress using NDE methods.  Hytorc® makes their own sockets and this may give an extra level of confidence.  However, in their safety note, Hytorc® only prohibits the use of altered, heavily used, damaged or chrome sockets.

Any socket can fail, so take steps to mitigate the result.  If possible, shroud the socket with a piece of pipe cut slightly bigger than the diameter of the socket and same height. If the socket fails, the pipe will hold everything inside. TGM is currently investigating a fiber impregnated tape designed to contain the debris. We also recommend tying off the head to prevent it dropping or flying off after a failure.

Be aware of your hydraulic forces.  Sockets are prone to failure when torqued more than twice the specified amount for assembly. Backup wrenches may not be rated for the torque applied.  Limit torque to the capacity of the weakest tool in the application.  Hytorc® publishes charts on their website which convert pump pressure to torque applied for each of their tools.

Finally, protect your personnel.  No one is to be in contact with the head or backup wrenches after initial clamping pressure is applied and until pressure is released. Determine the potential debris path and keep personnel away from the area. You can also use a piece of plywood or metal as a shield.  Face shielding is recommended as PPE for all personnel near the danger zone.

Remember that Hytorc® equipment is dangerous and must only be operated by trained individuals.  Best practice is to have the same person operate both the tool head and the pump.  When this is not possible, the pump operator must be in sight of the tool operator.  Three way communication must be used between them.

Loss of Lube Oil (Emergency Lube Oil Systems)

The International Association of Engineering Insurers found that the highest frequency of steam turbine failures worldwide is due to loss of oil. To minimize the effects of loss of oil events, all turbines have a backup or emergency oil system; however, checks of these backup systems are too often neglected. Should the backup systems be inoperable during a loss of power incident, the turbine can coast down with insufficient lubrication, causing expensive component failures. These failures can range from a loss of bearing integrity (wiped bearings) to major seal and rotating component damage, and they result in large costs to the turbine owner, not only in the repair of damage done, but in the cost of lost generation time.

Weekly maintenance checks on emergency lube oil systems should include verifying the adequacy of any battery backup system and testing the pressure switches and controllers that activate backup pumps. These tests should be performed to ensure the backup systems are fully functional should a loss of power or lube oil event occur. These simple efforts of prevention are inexpensive compared to the expenditures related to a turbine coming down without sufficient lube oil.