Key points
Considering the total life cycle of your instruments will help you decide when to maintain and when to replace. Wayne Deeks, Instrumentation Service Account Manager for ABB Measurement & Analytics Service, explains what’s involved in maintaining instrumentation through its operational life and what to do when it’s time to upgrade.
A time comes in the life of every measurement instrument when it becomes obsolete. Whilst it may be working perfectly, doing the job it is supposed to do accurately and well, the lack of any technical support or spare parts will mean it is nearing the end of its practical working life.
But what is obsolescence?
How is it defined and who says when an instrument has reached that status? What can be done to mitigate it and can it in fact be planned for?
Like many other items of equipment, instruments go through four phases in their lives. At each phase, particular levels of support are offered by the manufacturer.
These four phases are Active, Classic, Limited and Obsolete. The Active phase is the sales and manufacturing phase. At the end of this phase, volume manufacture ceases and the product moves into the Classic phase. Complete life cycle support is guaranteed throughout these two phases.
The Limited phase is where this product support is gradually ramped down, ending in the Obsolete phase when no product support is offered for the instrument. Most instrument vendors keep to the same scheme, with roughly equivalent durations for each phase.
On average, an instrument can have a lifespan of 10 -15 years as long as it continues to be supported and it is not unknown for users to still be using obsolete equipment that is 20 or more years old.
The danger of using instruments in the obsolete phase is that there is little or no possibility of replacing worn parts. This can lead to more inaccuracies in reading, resulting in a possible degradation in product quality. Inaccuracies in flow measurement of such commodities as gas or water could reduce a utility’s profits, while large offsets in critical instruments could have serious consequences for safety or result in non-compliance with regulatory requirements.
Also, a consistently inaccurate instrument could erode confidence in its ability to provide a reliable measurement, leading to staff ignoring its reading. This could prove particularly problematic in applications such as measuring the purity of water driving turbine blades, for example. Inaccurate instrumentation readings could lead to a build-up of mineral deposits on the turbine blades, causing significant pitting and other damage.
In these cases, the instruments are monitoring, not controlling, and users need to be fully aware that if an electrical fault occurs they will have to replace the instrument.
Get the details right to prolong process instrumentation life
The useful life of an instrument can be extended by ensuring routine maintenance, servicing and calibration is conducted according to the manufacturer’s recommendations. Another factor is having the right instrument that has been properly sized and specified for the application and which is able to handle operating conditions such as ambient temperature and vibration.
A user should also have contingencies for when the instrument does breakdown, including having an arrangement in place to call out the manufacturer or its agents to repair a failed instrument.
The response time can vary among manufacturers, who often offer different levels of response depending on the criticality of the unit. This can range from five days, down to three days or to 24 hours. Identifying the effects that breakdowns can have and identifying high risk instruments is essential in choosing the desired response time.
For super-critical applications that must be back on line to comply with regulations or to avoid serious losses in revenue, a 24 hour response may be vital.
An example was an ABB customer that was losing £20 to £30,000 for every 3-4 hours the instrument was down. Another is one of the UK’s main airports, which employs instrumentation to measure the run-off of cleaning chemicals used on the runway.
The airport needs a 90 percent up time for the instrument and every four hours off line counts as a full day, meaning 24 hour response is essential.
Power stations also need this type of fast response as they must adhere to strict emission levels laid down by the Environment Agency.
Tempting though it may be to specify a fast repair response from the vendor, this must be balanced against the criticality of the application, the losses incurred on failure and the increased cost of the rapid reaction.
Having access to spares and keeping a stock of consumables is also a factor. It was once common for instrumentation users to keep one unit in use and another on standby, though pressure on costs has made this practice less common than it once was. Similarly, fewer users now keep an extensive spares stock, preferring their instrumentation suppliers to hold bonded spares on their behalf.
Instigating a lifecycle plan means instrumentation users can plan upgrades and repairs effectively.
Manage the life cycle for best results
Understanding which phase your instruments are in and which course of action to take to maximise their life is the aim of a Life Cycle Assessment or LCA.
With ABB, the life cycle assessment begins with a life cycle audit. This highlights the condition of the equipment, its revision status and necessary maintenance needs for its operating environment. This helps formulate the best maintenance programme and identifies the appropriate migration points.
The life cycle audit has a number of features. The process begins with a site survey of installed instrumentation and analyser equipment, followed by an evaluation of the life cycle status of ABB and third party equipment.
The condition of the products is evaluated and their installation to ISO guidelines is confirmed. The final stage is a comprehensive inventory and life cycle report, including recommendations.
The life cycle audit offers a number of benefits. One of the main ones is that it provides knowledge of the equipment condition and revision status to aid maintenance planning and costing. It also helps set out a life cycle management plan to prolong equipment life and avoid premature failure, while also assisting with the development of life cycle planning and budgeting.
Once the exact condition of the equipment is known, the next stage is a life cycle management service to provide effective maintenance, migration and obsolescence planning as part of an integrated programme.
Essentially, the life cycle management plan implements recommendations from the life cycle audit and develops preventative maintenance schedules for installed devices based upon criticality. It also implements appropriate predictive maintenance technologies, as well putting in place any support functions needed.
Its central benefit is that it enhances the condition and reliability of instruments and extends operating life. It makes the correct resources and parts available to implement upgrades, while providing lower cost of ownership and minimal disruption.
Summary of Maintaining Process Instrumentation
Taking a rational approach to instrument servicing and replacement such as taking a whole life approach, is the only sure way to get cost-effective, extended use from valuable plant assets and in turn ensure that quality, safety, compliance, production time and revenue is maximised.
