Stresses in Piping systems

Hi all,

This is one of my favourite topics, since I had a large number of systems piping failures related to stress, mostly external.

One of the flange connections of the fire main systems on board a ship, couple of bolts used to break at the head frequently; more often if the ship had done some high-speed manoeuvres.  Initially, we used to change the bolt and live with it, but a nagging doubt came into our minds and we did a root cause analysis. What we finally found was that, the last pipe that fitted into the system was a little oversized and had been forced into its slot using a chain pulley, thus leading to a stressed piping section. Whenever high vibrations occurred, the stress used to increase, thus resulting in the flange securing bolts at one end shearing.

I came across a nice article on the topic. Please read and be enlightened on the topic.

Is-your-piping-system-prepared-for-stresses

KayCee

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Case Study on Advantages of Proper alignment of Rotating Machinery Assemblies

Hi,

Good, within tolerance, mechanical alignment between the driving motor and driven components is one of the basic health requirements.

I came across an excellent case study for which the link is given below.

Proper alignment helps one plant keep on pumping.

Please go through and be enlightened.

Kaycee

Control your repairs and spares, avoid costly downtime

Hi all,

All those who maintain capital assets by way of equipment, systems, buildings and vehicles cannot deny that they had to do some sort of repair work due to break down, reduced capacity, failures etc, some time in their day-to-day operations.

How the repairs were done, who all were involved, where was it done, What was done, when was it done and why did it become necessary are a few questions that need to be answered and recorded as part of the “Equipment / System History”.

I came across a very well written article on the importance of ensuring:

  • that the “Repair work” is assigned to the trained and skilled personnel.
  • that a well organised and clean workshop is used to do the necessary repairs, if not done on site, on location.
  • that quality spare parts and other material should be available in time, to avoid delay in work schedules.

The Link to the article is given below:

Reliability: Gain control of your repairs and spares to avoid costly downtime.

Reliability goes hand-in-hand with the quality of work done. It is essential that the repair personnel in the maintenance department are trained in their core skills and periodically tested for their skill retention. These people should be encouraged to learn new skill sets so that they also can rise in the hierarchy as deemed necessary.

The HR angle to skill retention in an organisation, getting better employee loyalty, better team development etc will flow from the way we try to motivate them.

Thanks

Kaycee

To Maintain or to Replace

Hi,

One question that plagues the mind of maintainers is the question of replacing equipment as they age, sometimes gracefully, sometimes catastrophically.

The current trend and availability of condition monitoring techniques can save the blushes for the maintainers as regards critical equipment.

Safety is the most convincing factor to seek replacement of equipment. Unsafe equipment / structures should be replaced without too much discussion since one safety incident could be more detrimental to the whole business than  the cost of replacement.

We could first categorise equipment using  a standard ABC analysis on “Cost aspects”:

  • Category A will make the bulk of low-cost items. Probably these could be replaced periodically as per some agreed parameters. Let us take the case of common battery chargers in service for charging various types of large storage batteries or traction batteries. We may replace these, whenever the items go faulty.
  • Category B items would be of medium cost, but would be lesser in numbers. This is the category that would cause some head ache in the “Maintain or Replace Conundrum”.  Let us consider the large number of motor driven pumps of 5 HP rating and above. The purchase cost is sufficiently high to call for some deliberation on the maintain or replace question, but not critical enough to take too  much of management time. If the population of such pumps are high in a facility, It may be worthwhile holding “hot spare switchgear-motor-pump assemblies” that may be used to replace a faulty assembly.
  • Category C list will contain the lowest numbers, but of high cost items. Much thought will be required in making the decision to replace in view of the capital expenditure involved. Let us consider a 1000 KVA Diesel Generator. Barring a catastrophic failure, it will have a standard life expectancy depending on the usage pattern and conditions of use. Simple condition monitoring techniques such as visual inspection, parameter variation analysis, oil spectrometry analysis and touch & feel of the equipment to understand changes in vibration levels would help in understanding the changes in conditions. Use of vibration monitoring and analysing equipment and thermal imaging will help in pinpointing problem areas and deciding on maintenance requirements. Planning for a replacement over a period of a few years is possible in this case.

Now, categorising equipment using  a standard ABC analysis on “Criticality aspects”:

  • Category A will again make the bulk of the list, made up of low criticality items such as small pumps, electrical switchboards, battery chargers, small capacity window type air conditioners, small capacity UPSs, small battery banks etc.
  • Category B will be the medium criticality items. They may not be show stoppers, but still could impact operations in a way. Multiple conveyor lines in which even if one fails, the product line does not stop.
  • Category C will be the high criticality items or a “Show stopper”. These need not necessarily be the most capital-intensive equipment in the facility. For example, a 50T EOT may not be as expensive as the sheet metal  presses and hammers in an automobile body parts stamping shop. The EOT could be a show stopper if it is not able to move the required pressing and hammering dies to and from the presses and hammers.

Combining the above two aspects, we will get a well categorised list of equipment that will help us in deciding on the maintenance and replacement policies.

Obsolescence

Electronic / Microprocessor based equipment go through obsolescence cycles periodically. Even core electrical and mechanical equipment may go through this process, but less frequently. The OEM will replace existing equipment with new designs time-to-time and declare the existing equipment not maintainable. This is another aspect to be considered in the replacement decision.

Take the case of UPS equipment. Every 5 to 8 years, such equipment may become obsolete. The batteries connected to the UPS will follow a different replacement cycle – more dependent on its own efficiency, discharging – charging  pattern and operating temperature.

Reliability

Reliability of equipment and systems is another aspect to be considered in the replacement decision.

The bath tub curve giveBath Tub Curve for Reliabilityn on the left  will provide some general guidelines to follow on the reliability aspects.

Apart from the infant mortality failure, equipment failure rates stabilise over a period and then start to increase with age.

Periodic maintenance scheduled at the right intervals will increase the stable period of operations.

With the current modular designs, changing of critical, comparatively shorter-life sub assemblies would stabilise the overall equipment / system reliability.

Mean Time Between Failures (MTBF)

This could be a part of the reliability study. For critical and capital-intensive equipment and systems, the analysis of MTBF could give indications on whether an equipment or sub-assembly is reaching the replacement threshold.

This study could be extended to those equipment with large population also. The analysis would aid in deciding on the make and model of equipment to choose as replacement for the failing ones.

Total cost of maintenance

Every maintenance activity consumes resources in the form of material, labour and overheads. Life cycle costing of equipment will provide insight into whether we need to re-think on the maintenance strategy.

  • In the case of low-cost items, it may be better to choose a work to failure strategy. Replace the item, every time it fails. Try and reduce the instances of failure by choosing a better make or model.
  • In the case of all other items preventive / predictive / Condition based maintenance strategies could be used. The conditioned based maintenance strategy will have some added monitoring costs, hence may be limited to critical equipment.

As and when the total maintenance cost gets close to the cost at purchase of the equipment / system, analyse all other aspects and decide on the replacement.

Benefits of having a good CMMS

The discussion above has indicated analysis of a variety of data while making the “Maintain or Replace” decision. A good CMMS suite will help the maintenance team to record all possible data on maintenance cost, breakdown, failure pattern, inventory cost, inventory carrying cost, equipment replacement cost, total maintenance cost etc. Analysis of the data will help in making an intelligent decision.

Thanks

KayCee

 

Five Pitfalls in Predictive Maintenance Techniques

Many organizations have cut their maintenance costs through Predictive maintenance efforts, simultaneously improving quality, safety, reliability and productivity. Unfortunately, there are a few pitfalls into which unsuspecting organisations get into while using the predictive maintenance approach. Identifying these traps will enable you to steer clear of them and set up an effective Predictive Maintenance program.

Learning to identify and avoid the recurring traps in your maintenance program will help you to be more effective in the application of both preventative and predictive maintenance techniques.

Pitfall #1: Capital Expenditure for equipment, but not for training

When maintenance budgets are submitted, and ultimately cut down, many companies fail to provide funds for adequate training to support the new Predictive maintenance related equipment. For example, some organisations invest on expensive infrared thermography equipment, but do not provide funds for proper training of personnel to exploit the full potential of the equipment. Thus the equipment would remain as an expensive toy with very little return on investment.

While OEM training on the basic operations and capabilities of the supplied equipment is essential, investment in the right kind of training is critical. OEM vendors may provide basic how-to-use training, but this may be inadequate for the users to utilise all the possible features and further more. Training by a brand-neutral or independent trainer for a particular technique using the new equipment would be beneficial on the long run. Training more than one person is also recommended to ensure year round availability of specialists. A word of caution – Do not train and allow too many people to handle expensive equipment since accountability for
equipment faults, damage etc becomes less.

Pitfall #2: Applying one predictive technique for all situations

If the only tool you have is a spanner, then every problem looks like a bolt. For instance, if you only have a vibration analyser, would you be able to identify loose connections in an electrical enclosure? Understanding the proper application of the different predictive tools is paramount to implementing and sustaining your system. Most predictive techniques are used together to improve reliability, aid in root cause analysis and improve safety. Organizations have obtained good results using a combination of predictive techniques like contact ultrasound, vibration analysis, oil analysis and thermography on gearboxes. They have been able to cut repair costs significantly by identifying a failing component instead of replacing an entire assembly.

Pitfall #3: Failing to properly re-inspect after corrective work is complete

The above scenario occurs all too often, in far too many operations. Predictive maintenance identifies problems that usually are undetectable by human senses. If the problem could only be seen with the predictive equipment, then the same reasoning should be applied when re-inspecting it. There are many instances where a repair has left the equipment in worse condition than before. For example, corrosion develops inside an electrical connection and maintenance makes the situation worse by tightening the connection. Or, in disassembling piping to repair an air leak, mistakes are made when putting the piping back together.

Without proper re-inspection, we would have no idea of the havoc we have caused in our own system. When you are using predictive techniques to identify a problem, ensure that your system schedules a re-inspection using the same technique.

Pitfall #4: Predictive Maintenance Corrective work orders get lower priority

Organisations that haven’t made the transition from reactive or breakdown maintenance to preventive maintenance will not be very effective in adding predictive maintenance to their work strategy. Maintenance supervisors will tend to prioritize more obvious problems.

All personnel involved in the maintenance process, especially those that have been working in a “reactive” maintenance mode need to understand that predictive work orders are a priority.

Predictive maintenance replaces parts before they fail—and this is a mindset that only comes with training and practice. The savings can be tremendous when parts are replaced before catastrophic failures take place to full machine assemblies.

Pitfall #5: Lack of a supporting maintenance system

While many companies will spend enormous amounts of time and money on tools, equipment, parts and materials, they will not focus on developing the foundation of a good maintenance organisation—the maintenance system. Using predictive techniques without an effective maintenance system in place only optimizes your reactive maintenance program. It will result in marginal savings and less-than-anticipated payback. Predictive maintenance is good, but you must have the other programs in place to support it.

Watch your step

In summary, recognising and avoiding the above mentioned five pitfalls of Predictive maintenance adds substantial value to any maintenance organisation.

Adapted from an article by Mark Pond of Marshall Institute – Posted by Maintenance Technology

Mechanical Maintenance Practices

Hi all,

In the maintenance field, alignment check of dynamic equipment plays a very important role. So does lubrication of moving parts. While browsing around for good articles on such maintenance topics, I came across the linked article that gives good insights on reasons for failure, remedies and other recommendations.

Tracking the causes of coupling failure
Bob Boyle, PlantServices.com
Explore coupling maintenance and the telltale signs of failure to maximize coupling life and ensure reliable system operations.

This is one area where a lot expertise is available. All viewers and readers are requested and invited to share their unique experiences on this topic.

Kaycee

Basic Steps to Arrive at Maintenance Plans – Part 1

Every industry and built environments (hospitals / office space / hotels) operate a large number of production and service equipment & systems in their day-to-day functioning. The scope of the site maintenance team encompasses preventive and predictive maintenance of a large variety of equipment, machinery and systems. The normal KRAs of the maintenance team are:

  •  Maximise availability & serviceability of site equipment.
  • Optimise usage of equipment and systems to ensure long service life and energy conservation.
  • Ensure that the logistics arrangements for carrying out maintenance activities are available in time, every time.

This guideline document covers the ten steps on deciding on “What”, “Why”, “Where”, “When”, “Who” and “How” the maintenance jobs are to be done.  All these and site-specific needs are to be identified while formulating the PM Schedules.

Aim

The aim of these guidelines is to help the Maintenance Managers and other staff to formulate effective Preventive and Predictive Maintenance Schedules for site-specific equipment, machinery and systems.

Approach

Step 1.          Identifying the equipment, machinery and systems that form a natural group is the first step. For example, Air Compressors, Dryers, Accumulators and the Air system would form a natural group – a “Compressed Air System.”

Step 2.          Breaking down the machinery, equipment and systems into manageable elements is the next step. In the above example, the Compressed Air System could be broken down into the following elements:

  • Air Compressors (If more than one type of compressor is feeding the system, these have to be listed separately). Main equipment prime mover driven pumps, mounted filters etc are considered as part of the main machinery.
  • Associated Pumps – mounted separately. This would cover items such as pumps for Pre-Lubricating oil, Standby Lubricating oil, inter-stage cooling water etc.
  • Control System.
  • Dryer with drier specific systems and equipment.
  • Accumulators.
  • Air system pipeline and other elements such as manifolds, valves, pressure relief valves, pressure gauges, sensors, down stream equipment etc.
  • Power supply system as applicable.
  • Prime mover for the compressor. If the prime mover is anything other than an electric motor, the specific systems for the prime mover are to be covered separately as the case may be. For example, a diesel engine driven air compressor, the diesel engine will have its own fuel / lubricating oil / cooling water / air intake / exhaust systems that are to be covered in the maintenance plan.

Step 3.          The next step is to assess the level of automation in the operation, age of the equipment elements and systems, operating profile, criticality and basis of operation (During shift / Continuous / Periodic / Intermittent). These parameters would help us in arriving at the level of attention that we have to give to the system as a whole.

  •  Automation in Operation.     Most of the latest commercial equipment comes with highly automated controls and data logging systems. This would mean that continuous manning of equipment is not required. A technician may need to check the system health physically once in a shift or so. For non-automated systems, a technician would have to manually record the operating parameters of the equipment periodically, whenever it is in operation.
  •  Age of Machinery Elements and Systems.            Older equipment and systems need to be assessed for their current condition to assess essential maintenance to be carried out immediately, followed by regular maintenance. The equipment and system history has to be studied by looking at the log books, spares consumption pattern, record of cost of maintenance, average running parameters, consumables consumption pattern etc.
  •  Basis of Operation.      The basis of operation could be as follows:
  • Continuous. Equipment and systems for a manufacturing process or process support may be on continuous duty. Say a compressed air system in a glass manufacturing plant. This would mean high system availability requirement, planned redundancy of equipment and system elements to enable periodic maintenance of all the items.
  • Shift Based.  The equipment or system may be operating only when the shifts are operating. An example would be the air conditioning system in an office space. The system may be operated only during the general shift timings when the office is manned. This would reduce the total system usage, increase time available for periodic maintenance, reduce need for redundant equipment etc.
  • Periodic.       There may be certain equipment or systems that are activated periodically. Chemical dosing systems that are operated as per a fixed schedule would be an example.
  • Intermittent.            There are certain machinery that are operated intermittently. A captive power plant may be kept on standby and will come into operation only when there is a power failure. Capital expense budgets will be the driving force in this case. Essential equipment would get budgeted, but after deliberations. With power shortage, power cuts and failures, extensive and regular use of captive power plants becomes imperative. Thus, maintaining the limited equipment that is essential, in good condition, will become a key area.
  • Equipment or System Operating Profile.  The operating profile of an equipment would mean the load condition at which it normally operates and the normal environmental conditions. Some of the equipment may have un-loader and loader mechanism by which the equipment adjusts its operation according to load. Generators running in parallel could be set to share the load automatically. This will avoid overloading of one generator while the other may be running at low load. Normally all equipments have a continuous rating. This is the loading condition in which it may be operated continuously. Normally the loading is restricted to just below the continuous rating so that optimum loading with least risk of damage is maintained.
  • Criticality.           For an industry handling heavy loads within the premise, a heavy-duty EOT crane may be the critical equipment that could be a show stopper if it becomes non-operational. For a “Communication Room or Data Centre”, UPS and HVAC will be critical requirements. For a hospital, uninterrupted power supply will be critical. Such criticality will drive the decision on maintenance frequencies.
  • Operating Conditions.            The operating environments also vary from site to site. Humidity, temperature, dust, corrosive chemicals, grit and slurry etc may be the limiting parameters considered. For example, the service life of centrifugal pumps handling corrosive chemicals or slurry would be lesser than pumps handling DM water.

Please do check in later for further installments on the topic.

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