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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Reliability | Hillbilly RCM |

I have seen people getting jittery when confronted with the term Reliability Centred Maintenance or RCM. The management jargon related to RCM makes it virtually difficult for the layman to understand the concept to its practical applications.

While operating gas turbine propelled ships in the Indian Navy, we had a few simple methods to listen to running machinery through rudimentary mechanical stethoscope – a long thin rigid copper tube with a brass disc attached. This was in addition to the more sophisticated on-line vibration measurement equipment, recording the vibration signature continuously. This data used to be periodically analysed to get the vibration signature. At that time, the recording was being done on board, but the data analysis was done by specialists sitting in their labs and we used to get reports on the health of the equipment on a monthly basis.

In one of my earlier posts, I had mentioned a “Look, Listen, Feel” strategy which could be the basic condition monitoring technique. I strongly feel that If Looking, Listening and Feeling are made integral parts of regular visits to the equipment, it forms a practical method in improving reliability of equipment and systems.

Another management jargon that has caught on is “Autonomous Management”. This talks of the equipment and system operators joining hands with the maintenance personnel and getting cross trained with each other’s functions. The operators will be made responsible for the first line maintenance of the equipment or systems that they are in charge of and the maintainers will be trained in basic operations of the same equipment or system. This has the following advantages:

  • Improved feeling of ownership among both groups – operators and maintainers
  • Both the groups understand the equipment or system operations and the nuances of reliable operations
  • Flexibility in operations and maintenance – Who to do what, when, where?
  • Better operator – maintainer relationships. Lesser “We – They” conflict
  • Resulting increase in reliability and Overall Equipment Effectiveness (OEE)

I came through an article in an old issue of Plant Services, covering a practical simple method to analyse reliability and achieve RCM. The link is given below:

Reliability | Hillbilly RCM | Plant Services.

Please read through to help you on the RCM path. No big statistical analysis, probability theory, mathematical modelling etc are involved.

Regards

Kaycee

CMMS/EAM Software Review: 9 trends spurring CMMS/EAM evolution

Hi,

Plants Services is one magazine that I subscribe to. It comes up with highly readable material, written by knowledgeable people.

The latest issue had an article on CMMS / EAM evolution. Please click on the link below to access and read the same.

CMMS/EAM Software Review: 9 trends spurring CMMS/EAM evolution.

Regards

KayCee

Reliability: How to develop an effective root cause failure analysis process

Hi all,

We all wish that the equipment and systems that we operate would work for ever, efficiently, effectively and productively. Though the reliability factor gets embedded at the design stage itself, there are “Ifs and buts” that get into the operation. With the current corporates culture tends to move towards “No defects”, reliability in operations becomes important.

All the maintenance effort is focused to this end, but in real life, failures do occur and do recur too. This is where the reliability study will help. Root cause analysis is a tool to understand the most likely cause for a specific failure and implement processes and procedures to avoid recurrence.

We all would have done this process mechanically, informally many times. Making such a study formal helps in making systemic corrections.

Here is a link to a very well written article on the topic.

Reliability: How to develop an effective root cause failure analysis process.

Read and be more well-informed.

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

Pipe Connections – Care in alignment

Hi,

This one is from experience on board ships.

While serving on one of the ships, we had a recurring problem of bolts shearing on a fire main header connection to the ring main.

Root Cause Analysis

A large number of pipes in this section of the fire main were replaced with new ones during the last ship refit since inspection revealed extensive internal corrosion and wall thinning by way of bends. What all had happened till then?

The system is a little complicated since it crosses a few decks and watertight bulkheads through watertight glands. There were a few bends and joints in the way. Where, How, Why?

 

The new pipes were made using the existing ones as template or sample. A few of the older pipes found serviceable were also used. What, Where?

While fitting out the pipes onboard, with the combination of old and new elements, the pipe alignment had gone haywire (the magnitude could be in millimeters per instance though). The pipes were fitted as it is and the cumulative misalignment at the last flange to be connected must have been high.What, Where, How, Why, Who?

The last two flanges were brought together face to face using force and buttoned up, with gaskets and gasket eliminator paste. No leaks were reported during the ensuing trials.How, Who, Why, Where?

Conclusion.

The bolt shearing problem started the moment the ship started sailing. This could have been due to the induced vibration on the system pipe line aggravating the strain on the bolts (already stressed due to the forced connection).

Immediate Remedial Measure.

The last section of pipe was removed. A template was made to remake a new pipe to exact dimensions. The system was buttoned up using the newly made pipe. No more bolt shearing…….wow.

How to avoid recurrence?

The above mentioned scenario is applicable to any piping connection. In pipe laying, it is essential that all pipes are made as per a layout diagram. The last pipe connecting to more rigid members such as a pump or gland or fixed flange need to be made as per a template with accurate measurements.

In some cases with Copper and Aluminium pipe systems, age hardening occurs. Both Copper and Aluminium pipes are amenable to damage while in use or in storage. Alignment check before closing the last element of pipe is essential to avoid flange stress. The larger the pipe diameter, the more pronounced the problem.

Kaycee