Contrary to popular opinion, all workers can prevent themselves from getting hurt. The easy way to avoid pain is to observe how others have taken risks and been injured, rather than learning the hard way–from your own injury. That’s common sense! By avoiding unsafe acts and practicing common sense, your work will go smoother, with less chance for accidents.
The experts say at least 80% of industrial accidents are caused by unsafe acts on the part of employees–and not by unsafe conditions. Although employers are required by law to provide a safe and healthful workplace, it is up to you to be aware of your work environment and follow safe work practices. Statistically, most accidents are caused by unsafe acts, including:
Being In A Hurry – Sometimes there is more concern for completing a job quickly instead of safely. Take time to do a good job and a safe job.
Taking Chances – Daring behavior or blatant disregard for safe work practices can put the whole work team at risk. Follow all company safety rules and watch out for your fellow employees. Horseplay is never appropriate on the job and can lead to disciplinary action.
Being Preoccupied – Daydreaming, drifting off at work, thinking about the weekend, and not paying attention to your work can get you seriously hurt or even killed. Focus on the work you are paid to do. If your mind is troubled or distracted, you’re at risk for an accident.
Having A Negative Attitude – Being angry or in a bad mood can lead to severe accidents because anger nearly always rules over caution. Flying off the handle on an outage is potentially dangerous. Keep your bad moods in check, or more than one person may be hurt. Remember to stay cool and in charge of your emotions.
Failing To Look For Hidden Hazards – At many jobsites, work conditions are constantly changing. Sometimes new, unexpected hazards develop. Always be alert for changes in the environment. Hidden hazards include spilled liquids that could cause slips and falls; out-of-place objects that can be tripped over; unmarked floor openings one could step into; low overhead pipes that could mean a head injury; and other workers who don’t see you enter their hazardous work area.
Remember to stay alert for hazards, so you won’t become one more accident statistic: You can do a quality job without rushing. Maintain a positive attitude and keep your mind on your work. This is just common sense–something smart workers use!
Common Sense Safety
/in Safety Tips /by Mike.LakeThe experts say at least 80% of industrial accidents are caused by unsafe acts on the part of employees–and not by unsafe conditions. Although employers are required by law to provide a safe and healthful workplace, it is up to you to be aware of your work environment and follow safe work practices. Statistically, most accidents are caused by unsafe acts, including:
Being In A Hurry – Sometimes there is more concern for completing a job quickly instead of safely. Take time to do a good job and a safe job.
Taking Chances – Daring behavior or blatant disregard for safe work practices can put the whole work team at risk. Follow all company safety rules and watch out for your fellow employees. Horseplay is never appropriate on the job and can lead to disciplinary action.
Being Preoccupied – Daydreaming, drifting off at work, thinking about the weekend, and not paying attention to your work can get you seriously hurt or even killed. Focus on the work you are paid to do. If your mind is troubled or distracted, you’re at risk for an accident.
Having A Negative Attitude – Being angry or in a bad mood can lead to severe accidents because anger nearly always rules over caution. Flying off the handle on an outage is potentially dangerous. Keep your bad moods in check, or more than one person may be hurt. Remember to stay cool and in charge of your emotions.
Failing To Look For Hidden Hazards – At many jobsites, work conditions are constantly changing. Sometimes new, unexpected hazards develop. Always be alert for changes in the environment. Hidden hazards include spilled liquids that could cause slips and falls; out-of-place objects that can be tripped over; unmarked floor openings one could step into; low overhead pipes that could mean a head injury; and other workers who don’t see you enter their hazardous work area.
Remember to stay alert for hazards, so you won’t become one more accident statistic: You can do a quality job without rushing. Maintain a positive attitude and keep your mind on your work. This is just common sense–something smart workers use!
Copper Resistance Testing
/in Generator Tips /by Mike.LakeTest Setup & Execution. The main and neutral lead connections should be broken and open. The lead ends should be free and clean of surface contamination so that the test probes make good contact. Copper resistance testing is performed with a Digital Low Resistance Ohm Meter (DLRO) test set. The DLRO instrument is extremely sensitive. Poor contact and circuit set-up can either produce erroneous readings or no readings at all.
One probe of the DLRO is connected to one lead of an individual phase, and the other probe connected to the other lead of the same phase. A reading (generally to the fourth decimal place) in ohms resistance is measured and recorded. This same process is repeated on the second and third phase. The ambient air temperature and humidity should be recorded as well.
Interpretation of Results. Temperature significantly influences the resistance of a dielectric as well as a conductor. For this reason, the copper resistance measurement should be corrected to standard (typically 40°C).
The original equipment manufacturer normally records and documents the as-built phase-by-phase copper resistance measurements. These are used as the baseline by which all future readings can be compared.
An increase in in copper resistance indicates the presence of some form of high resistance issue (i.e. broken conductors, cold braze joints, turn-to-turn shorting, incorrect connection, incorrect number of turns or stranding, open circuit). Additional testing will be required to determine the specific cause of the variant reading.
Standard. IEEE Standard 11 8TM-1 978, IEEE Standard Test Code for Resistance Measurement.
Test Equipment. A Megger, Model DLRO-10 or comparable is recommended. Kelvin and Wheatstone bridges are also used to measure resistance.
Slips, Trips, and Falls
/in Safety Tips /by Mike.LakeMost common locations for falls:
Falls can be prevented – Ladder Safety
Casing Repair – Part 3: Distortion & Erosion
/in Steam Turbine Tips /by Mike.LakeCasing Distortion
Casing Distortion becomes a strong likelihood when the units accumulate operating cycles. The most common causes of distortion are steady state and transient thermal stresses which can occur within all turbine sections (HP, IP, LP). Inner casings distort more easily than outer casings due to their thinner cross-section and higher temperature differentials across the casing walls. Distortion typically causes problems during disassembly and reassembly. Some examples of this are bolting interferences, gaps at the horizontal joint, galling of the fits and misalignment of the steam path seals. These problems can lead to steam leakage and rubbing. Internal leakage due to distortion reduces efficiency and power output, while leakage to atmosphere and internal rubbing can both cause a forced outage.
Water induction can cause extreme distortion of the inner cylinders. This can damage internal steam path components and lead to forced outages. Inner casings as well as valve bonnet covers can become severely warped and may require extreme measures to remove and replace.
Casing distortion can be corrected by welding, machining, localized heating and rounding discs inserted during stress relief. See previous Tips in the series for considerations in employing these methods.
Erosion
Damage from erosion affects different designs at different locations, but both rotating and stationary components are vulnerable. Erosion typically takes place in the LP section where steam enthalpy drops below the saturation point. Crossover pipes and inlet areas to the LP section could increase in roughness as the surfaces wear unevenly. Support struts may thin or be cut through. Moisture erosion can also take place in the exhaust ends of HP and IP sections if the turbine operates for long periods at low load or goes through frequent start-ups. Horizontal joints may erode and leak between stages and stationary blade support rings may erode as well as crack.
Casings, diagrams, hoods and crossovers are usually made of carbon steel or cast iron. These materials erode approximately 20 times faster than blading material made out of 400 stainless steel.
Erosion can contributes to major damage. Repairs must be aimed at improving the erosion resistance of the steam path and support surfaces. Methods also must be examined for reducing steam moisture content and the size of droplets.
Eroded areas can be rebuilt. Stainless steel or other erosion resistant weld metal can be applied to eroded seal surfaces such as horizontal joints, flow guides and diaphragm inner and outer rings and joints. Fabricated stainless steel liners can be welded inside of crossovers, seal areas and inlet flow areas of casings. They may also be applied over support struts to protect the existing cast iron, steel or low alloy castings. No stress relief is required in most welding applications. Epoxy or ceramic coatings may be suitable for surfaces that are not suitable for weld overlay.
For more information on your particular application, please contact Mr. Turbine®.
Casing Repair – Part 2: Welding Considerations
/in Steam Turbine Tips /by Mike.LakeNon-stress relieved welds have the advantage of lower cost and shorter outage time. The disadvantage is that the weld can be short lived. The procedure follows this outline: A preheat of about 500 degree F or greater is used. A shielded metal arc weld is performed with a non-matching high nickel content filler. This use of dissimilar metals as filler can lead to low cycle metal fatigue. No post-weld stress relief is performed but the preheat conditions are maintained throughout the process.
Stress relieved welding offers the best potential for a long repair life, but is complicated and time consuming. The procedure follows this outline: A lower preheat of about 300 degree F is used. A shielded metal arc or metal inert gas weld is performed with a matching metal content filler. The casing is then placed in a furnace and raised to a temperature of over 1,000 degrees F. The exact temperature depends on the alloy, the procedure and the application. Much higher temperatures may be required. There are no problems with differential expansion during turbine operation since the weld uses matching filler metal.
The pre-weld residual stress levels in the casing must be carefully assessed to increase the probability of a successful weld. The high levels of residual stresses in the casing can combine with the added stresses of welding to cause uncontrolled distortion and hot cracking during the stress relief phase. Residual stresses generated by the weld passes can be reduced through techniques such as grinding, peening between passes, and peening and grinding. Therefore, the welding procedure must be performed by a skilled contractor.
The best way to control distortion during stress relief is to bolt the casing halves together and place the assembly in the furnace. This would be most applicable to an inner casing that can be easily removed from its outer casing. If only the upper half of the casing is going to be repaired, a thick plate can be bolted onto the horizontal joint as a substitute for the lower case. Distortion can be further controlled by inserting custom fabricated rounding rings or disks into the assembly before thoroughly bolting it together.
If the facility has ample room, a portable furnace can be built on-site. Otherwise, the assembly must be sent out for this process. If the assembly is too large for the furnace, stress relief can be done on a local area of the case, allowing suitable temperature gradients away from the weld areas. Whatever the location, the temperature of the furnace and the assembly must be stringently monitored during the entire stress relief process. Multiple heat cycles and possible re tightening of the joint bolting between cycles may be necessary. This is a process which has been refined over the years and continues to get better. Again, it is always a good practice to perform an assessment prior to performing any of the above procedures.
The next Turbine Generator Tip in the series discusses casing distortion and erosion problems. For more information on your particular application, please contact Mr. Turbine®.
Knife Safety
/in Safety Tips /by Mike.LakeAll cuts should receive first aid. Even the smallest cut can become infected, so treat all cuts properly. Always use a knife only for what it is intended. Never use it as a screwdriver or pry bar. Never use a knife that is defective. Keep knives sharp and in good condition. A dull knife can cause you to put too much pressure on the object you are trying to cut. The blade could slip and slice you or someone nearby.
The principal hazard when using a knife, whether on or off the job, is that the user’s hand may slip from the handle onto the blade, causing a painful and serious injury. A handle guard will reduce this hazard. Another cause of injury is the knife striking the free hand or the user’s body.
Industrial knife safety principles remind us to always make a cutting stroke away from the body when possible. Adequate protection should be worn to protect the body and provisions made to hold the material steady. Steel-mesh gloves are available in select industries, such as meatpacking, where materials must be held in close proximity to the knife. TGM carries these steel mesh gloves in every tool set we own. We are in the process of getting Kevlar gloves as well.
When on the job, carry a knife in a sheath or holder over the right or left hip, pointing backwards. Otherwise, a fall could cause a serious leg injury. Storage of knives is also an important safety factor. Cutting edges should be covered and not exposed. Knives should be kept in their proper place and not left on benches or on the floor.
If you are using the right knife for the job, it should cut without great difficulty. When you have to resort to force to make a knife cut, then you are headed for trouble–it could result in an injury to you, damage to the knife, or damage to the material that you are attempting to cut. Remember this, “our patience will achieve more than our force.” That is a good point to remember when using a knife.
Forklift Safety
/in Safety Tips /by Mike.LakeAccording to OSHA, forklift overturns are the leading cause of fatalities related to the use of forklifts and result in 25% of all forklift deaths. Other incidents that are associated with using forklifts include falling from a forklift, loads falling on workers, not using a seat-belt and being ejected or not following the proper procedures while traveling on grades or ramps.
With the proper training forklift operators will gain the knowledge and skill required to create a safe environment. When operators do not have the proper training problems arise and often lead to accidents and deaths.
Ask yourself the following questions:
1. Have you received training to operate a forklift?
2. Do you know how to properly report damage or problems during your shift?
3. Are you aware of any mechanical issues before operating a forklift?
4. Do you know how to properly operate a forklift on grades and ramps?
5. Do you know what to do if your forklift is overturning?
6. Do you know how to determine load capacity?
7. Are you using seat-belts properly while operating?
8. Have you received training on proper fueling?
9. Do you know how to properly mount and dismount a forklift?
10. Do you have the necessary information needed to comply with OSHA regulations?
(Courtesy of Crane Tech)
Casing Repairs (Part 1: Cracking)
/in Steam Turbine Tips /by Mike.LakeCracking is the most common problem on utility units built before 1970. Cracking typically occurs at the steam inlet areas on the HP and IP sections, where transient thermal stresses can exceed the yield point of the casing material. Cracking may be found on the interior surfaces of steam chests, valve bodies, nozzle chambers, seal casings, diaphragm fits and bolt holes. In the low pressure section (LP) cracking can also occur at the inlet sections, inner casings, support struts, bolt holes and diaphragm fits. Computer modeling and advanced alloys have reduced the likelihood of cracking in more modern units, but cracks can develop in any unit, especially those experiencing more stop/start cycles.
Every crack must be fully analyzed before attempting repairs. NDE inspection must be performed at a minimum. Radiograph inspections may provide greater assurance by revealing the extent of the crack in relation to its location and the thickness of the surrounding area. Some OEM’s have a detailed customer letter on known areas of potential cracking, their particular process to map out these cracks, and the proposed corrective action and potential life expectancy.
Although grinding is a common repair method, it can increase the potential for new cracks if improperly applied. Cracks in steam chests can potentially expand, making repairs more costly. Grinding on cracks in older machines may open up hidden voids in the casing, making the condition much worse. Another problem is that even when an NDE shows that cracks have been removed by grinding, very small undetectable cracks may still be present and may lead to future larger cracks.
Welding of cracks is another common repair method. There are two distinct procedures for welding: stress relieved and non-stress relieved. Non-stress relieved weld repair has the advantage of shorter outage duration but can fail much sooner than a stress relieved weld. This complicated topic will be discussed in our next Turbine Generator Tip in the series.
Mechanical Repairs can be applied to cracks, but must be properly designed to redistribute tensile loading away from the crack area. One method is to apply stitches. Metal inserts are placed across or along the crack and drilled and pinned to the case (see picture). Another method is to place bars or dog bone shapes across previously ground out areas. A more effective version of this method uses precision machining and the application of a lobe-lock designed through finite element analysis. The material used must provide adequate load properties and must be ductile at all temperatures to prevent cracking of the lobe-lock.
Mechanical repairs have several advantages. The repairs can be performed in place, with no possibility of casing distortion because there is no heating or welding. Machining durations are shorter and easier to quantify. These repairs can also extend life to the area (vs. welding). Disadvantages are that the mechanical repair is conducted on a low cycle fatigue crack and concentrated in an area surrounded by non-cracked material.
The next Turbine Generator Tip in the series discusses stress relieved vs. non-stress relieved welding. For more information on your particular application, please contact Mr. Turbine®.
Crane Safety Revisited
/in Safety Tips /by Mike.LakeJust when you think you have all the bases covered, the “impossible” happens. During a lift on one of our recent outages, the idler pulley and mounting bracket for the drive on the overhead crane fell approximately 25 feet. Fortunately no one was injured. We have discussed the need for pre-outage crane inspections in previous Safety Tips, identifying the need for an OSHA-compliant inspection before the outage. The customer had conscientiously performed the inspection, and we had examined the report. In a post-incident report, the company’s preferred crane inspection vendor discovered the root cause was an alignment issue with the driven sprocket for the trolley. The company implemented two corrective actions: the crane vendor installed a safety cable to prevent the bracket from falling in the event of a failure, and an alignment protocol was added to the inspection checklist. Discussions are continuing on additional preventive measures.
For TGM’s part, we recognize that we have a responsibility to not only request the inspection report, but to read and analyze it. We have discovered that this crane vendor includes an Inspection Report Key along with the report which gives a Priority Code and a Condition code for each finding. These codes help identify the importance of the finding and the need for corrective action. These codes are specific to this particular vendor. Others may use a different key or not have one. We will now be asking for an Inspection Report Key in addition to the report so we can double check that all deficiencies have been corrected. We will also be asking for the report with enough lead time such that any corrections can be made before the outage.
AC & DC High Potential Testing Fact & Fiction
/in Generator Tips /by Mike.LakeWhich is better: AC or DC Testing? Will these tests hurt my generator? Here are the facts:
In conclusion, AC high potential testing is better suited for acceptance proof testing of new equipment (i.e. coils, bars, and stator windings). DC testing is better suited for in-process proof testing, maintenance proof testing, and controlled over-voltage testing of new and/or used equipment. AC or DC high potential testing should not be used as the sole source of diagnostic or acceptance data. An experienced and qualified generator testing specialist will recommend a testing protocol specifically suited to your machine’s life cycle and operating history.
* A one minute AC or DC high potential test equates to approximately 11 hours of useful life expended. Assuming that a stator winding has a nominal 30-year life expectancy (263K hours), this would equate to only a 0.0004% reduction in service life per test.