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

Condition Based Maintenance – Monitoring Tools

Hi,

I keep getting updates on new products used in the maintenance field through various online subscriptions.

Here is a link that shows the us of Ultrasound devices in the condition based maintenance strategy. I am not trying to sell the product, but am just trying to propagate the techniques involved. Please connect to the link given below and learn more.

http://www.uesystems.com/new/applications/

KayCee

Look, Listen and Feel – in Condition Based Maintenance

Hi all,

With due respect to all the gadget geeks and proponents of high-tech equipment to carry out condition based maintenance; the age-old classic forms of observations as indicated below are still valid in the field of condition based maintenance; probably as the first information report function.

Look ………. Listen ………. Feel!

The basics of good maintenance start from the careful, systematic, periodic inspection of equipment and system elements – the first step. Recording of observations is the second step. Analysis of the observations by a maintenance team leader would be the third step.

Essential Safety Precautions for the Look / Listen / Feel Work

Wear all essential personal protection equipment prescribed for each installation. Examples – for high noise areas, ear defenders are a must; eye protection is essential where high dust, fumes, vapours, flying sparks etc conditions exist. Safety shoes are required to be worn in all conditions. Rubber soled shoes with fibre re-inforced toes are to be worn while working on electrical panels and equipment.

Individuals must be deployed for such jobs only after successfully being certified in safety aspects and equipment skills.

Visual inspectionLook

Before starting an equipment or systems: Good maintenance practices exhort users and maintainers to do a full visual inspection of equipment and systems before they are put into use, each time and every time. Such a visual inspection could reveal tell-tale oil or lubricant leaks, discolouration of protective paint due to overheating, corrosion spots, damaged parts, missing elements such as belt / chain guards, dust and debris collection, physical obstruction etc. Clearing all the abnormalities before putting the equipment or systems to use will increase their reliability.

Identifying “Lock Out Tag Out (LOTO)” Conditions: Visual inspection of control (mechanical / electrical) elements will help in identifying the LOTO conditions. In case the equipment is tagged out or locked out; operations are not possible till that condition is cleared by the person who locked it or tagged it.

Running equipment or systems: Periodic visual inspection of equipment or systems while in operation is also essential.

  • This could be done manually by visiting each equipment, looking at the equipment as a whole, checking the relevant critical parameters from their respective meters, checking for abnormal visual vibrations, checking for visible leaks, checking for overheating, checking for spray or flow quality / quantity (example – cooling tower water nozzles),
  • Alternatively, for large installations with high automation and central controls, the visual inspection could be through CCTV cameras, monitoring of parameters through data loggers, online vibration measurement, etc.

ListenListen

This is mostly applicable to equipment with rotating elements (motor driven pumps, fans, compressors etc).

Loose components or sub elements on the equipment may cause audible rattling noise. If left unattended, these could lead to consequential damages.

This technique needs some skill and long involvement of the operator or maintainer with the equipment under his or her charge. The operator / maintainer need to develop a skill on “what to listen to” and on how to identify “wrong noise”. This comes from experience.

On the long run, an operator will be able to make out the change in noise at a motor bearing or a fan air cutting noise due to blade damage. At this point it may be subjective, but a requisition for more precision measurements could be initiated before a major damage occurs.

A long stem screw driver or a simple mechanical stethoscope made out of thin, rigid, long copper tube with a small brass ear cup (a simple washer would do) attached to it could be used as an effective listening aid.

Please be wary that very noisy equipment should not be listened to with unprotected ears and the listening aids mentioned above. Prolonged exposure to loud noise could lead to permanent hearing loss progressively.

FeelFeel

The “Feel” factor is an equally important tool in condition monitoring. One needs to be a bit cautious on this aspect since many of the running equipment could have hot surfaces and may not be directly touchable, without causing harm. On the same lines, there could be system elements that run very cold and touching them with unprotected hands could cause cold burns or skin peeling. The Maintenance managers need to decide on what can be touched to feel.

Safety is very important here since the “Feel” actions are generally done on running equipment. Care should be taken to avoid putting the palm very close to moving parts

The “Feel” gives you some idea on the difference in temperature, non-visual vibration level changes, flow quality (turbulent or otherwise), presence or absence of flow, presence or absence of a liquid in a container or pipe, heaviness or lightness of an item, rigidity or flexibility of an item, speed / velocity changes etc. “Feel” is  through the skin and the palm is the best suited body part for the purpose.

Combination of Look, Listen and Feel

Practised together, the above combination provides a very thorough basic condition monitoring technique. experience on the field and safe working habits bring in a slew of benefits in OEE and reliability.

One thing good about this is that it is a value addition to the service rather than eating into a lean and mean budget allocation.

The observations from the above technique could lead to more precise measurements of temperature gradient using a thermal imaging camera, vibration monitoring using hand-held equipment etc.

Visual Factory

Appropriate signage placed at strategic locations could make the Look, Listen and Feel inspection systematic.

Place pictures of eyes where visual inspection needs to be done. Pictures of ears and palm would indicate the listen and feel activities.

Added to these, station markings arrows could be marked on the ground indicating which positions the operator or maintainer should take and direction to face the equipment to make an observation.

Further arrow markings to indicate the direction to be taken while making observations could be done to optimise effort and time taken for observations.

Tail Piece

Smell The human nose can discriminate difference in smells. For example, the smell of overheated or burning oil in a diesel engine has a very recognizable odour.

Heated or burning electric insulation also has a very distinct odour.

The smell of a burning flourescent lamp choke is very discernible.

Smell of a dead rodent in a ventilation duct can be very disturbing.

So, the nose also can be a very reliable sensory organ in equipment / system condition monitoring.

Comments are solicited on my thoughts expressed in this post.

KayCee

Hydraulic Systems Hygiene

Hi all,

A well tuned hydraulic system gives trouble-free operations. A few regular problems that crop up are leaks in the system leading to starvation of oil and air bubbles in the system due to ingress of air. 

Hydraulic oil and systems are very sensitive to contaminants. These systems need to be maintained in very hygienic conditions. Filtration is one of the modes of keeping the hydraulic fluid clean.

The linked article covers the modes of filtration with their benefits and drawbacks.  

Clean up hydraulic circuits
Phillip Johnson, PlantServices.com
Selecting the proper filter leads directly to greater uptime, lower maintenance expense and longer machine life.

Kaycee