Posts Tagged ‘technology’

Why it pays to pay more for safety (Part 2)

February 19, 2014

In our last blog, we looked at the real costs that can arise where safety takes a back seat and explained some of the factors behind the higher costs of specialised instrumentation and control equipment for safety applications.

In this blog, we’ll be looking at the parameters that define the overall effectiveness of a safety loop and will show why opting for higher integrity equipment can save money in the long term.

Let’s start by looking at the required Safety Integrity Level (SIL), as defined by IEC 61508. IEC 61508 is the “mother” standard that spawned corresponding “daughter” standards for the process industries (IEC 61511), nuclear facilities (IEC 61513) and machinery (IEC 62061). It is not a legal requirement for British businesses, but HSE accepts it as good practice.

Confusion can often arise when it comes to designing a safety system as it’s not as simple as just applying a blanket SIL to cover an entire process. Instead, operators must first consider the individual safety instrumented functions (SIF) within a process, these being the functions of a given device that are necessary to protect against a hazardous event. This can then be used as the basis for designing and engineering the safety system solution, consisting of the inputs, the logic solver and the final elements, including instrumentation.

As a general rule, it is almost always better to design risk out of a process before installing specialised systems to control it. This will often reduce the required SIL and therefore the cost of the safety systems needed to deliver it.

Next is the average probability of failure on demand (PFD). The acceptable PFD of a system varies depending on the required SIL as well as the required mode of operation of the safety instrumented function, which is the frequency with which a safety instrumented system will be used. For a safety function operating in a low demand mode of operation, the PFD ranges from ≥10-2 to ≥10-1 for SIL1 to ≥10-5 to ≥10-4 for SIL4.

The overall PFD is calculated by combining the PFDs of all the individual components in the loop. For example, a transmitter designed for safety will typically offer a lower PFD than a standard transmitter, bringing down the overall PFD of the system and potentially raising the SIL.

Other factors that determine whether an individual instrument is suitable for a particular SIL are the safe failure fraction (SFF) and the hardware fault tolerance (HFT).

The SFF is a function of the number of safe failures, the number of dangerous undetected failures and the number of otherwise dangerous failures that can be rendered safe by being detected, for example, by installing self-diagnostic capabilities.

The HFT indicates the number of faults that need to crop up within a device before a safety failure occurs. For instance, the failure of a standard transmitter might result in the output from a transmitter freezing on its last setting, but a transmitter designed for safety might revert to a prearranged fault setting, which could in turn trigger an alarm. Built-in redundancy can also raise the HFT from 0 to 1.

The integrity level provided by a given combination of SFF and HFT varies depending on whether the overall safety system is a well-proven Type A or less well-understood Type B, according to the IEC 61508 standard. The other key factor to be considered is the systematic capability. This relates to factors such as the methodology, techniques, measures and procedures used in the design and engineering of the element itself and the integration of elements to form the safety system.

The other thing to look out for is the quality of documentation available from the equipment supplier. Are their instruments certified by independent testing bodies? Have they got a sufficiently strong track record for the user to be confident that the equipment is “proven in use”?

Savings soon add up

Independent tests and extra paperwork may not sound like a cheap option, but there are several ways in which opting for higher integrity equipment can save money in the long term.

The first is that the safety systems do not need testing as often to check that they are still working properly. The required proof test interval can be extended significantly if equipment can demonstrate a higher HTF and a lower frequency of dangerous undetected failures. This will deliver lower operating costs for any user, but the difference is likely to be especially significant in industries such as offshore or nuclear, where gaining access to the systems can be difficult and expensive. It might, for example, mean the difference between sending inspectors out to an oilrig by helicopter every three months or once a year.

The second area where savings can be made is in insurance. In fact, some insurers now insist on complying with particular safety integrity levels before they will agree to provide cover.

However, it is the prevention of accidents that still offers the biggest potential financial savings, not just in terms of financial penalties, but also the impact that an accident or incident can have on a company’s share price and reputation. Add to this the imperative to protect personnel and be a good neighbour to the surrounding community and the case for excellence in safety systems is compelling – whatever the state of the economy.

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Is your thermowell up to standard?

November 8, 2013

By Steve Gorvett, Temperature Product Specialist, ABB Instrumentation

Did you know that recent amends to manufacturing standards may mean that some of your thermowells aren’t up to scratch?
Thermowells are often so fundamental to plant safety that any design flaws can have disastrous effects. By way of example, in 1995 a thermowell failure in the coolant loop at the Monju fast breeder reactor in Japan closed the plant for the next 15 years. It’s for this very reason that there are tight industry manufacturing standards that govern thermowell production.

Following some catastrophic failures (including the Monju disaster) the American Society of Mechanical Engineers decided to amend the ASME PTC 19.3-1974 standard to which these thermowells were designed to.

The latest revision of the ASME PTC19.3 standard makes use of significant new knowledge about the behaviour of thermowells, compared to the criteria laid out in 1974. The standard evaluates thermowell suitability with new and improved calculations for various thermowell designs and material properties. It also takes some detailed information about the process into account.

In particular, the standard looks at the incidence of vortex shedding. This is the phenomenon where vortices formed in the wake of the thermowell move from side to side; this is what causes vibrations in the thermowell. If this vortex shedding rate matches the natural frequency of the thermowell, resonance occurs, and dynamic bending stress on the thermowell increases.

The frequency ratio is the ratio between the vortex shedding rate and the installed natural frequency. In the old standard, the frequency ratio limit was set to 0.8. The new standard stipulates that in some cases, the limit should be set to 0.4. The new possibility of having a much lower frequency ratio limit of 0.4 means tighter design constraints in many cases. As the majority of existing assets will have been designed to the 1974 standard, the new 0.4 frequency ratio means a lot of thermowells will NOT pass the new standard.

Re-evaluation and re-certification services are available. Operators will need to consider the implications when an existing thermowell fails the new calculation. If process conditions change, for example increased throughput for a part of plant, this should also be evaluated.
At a brownfield modification we recently examined for new process conditions, 29 existing thermowells were evaluated under existing and new conditions. Only six passed the new standard under existing conditions!

Bearing in mind what happened at the Monju fast breeder reactor in Japan, which did conform to the 1974 standard, isn’t it about time you reviewed your thermowell installations?

New in-situ monitor from ABB opens up expanded possibilities for laboratories and pilot plants

June 6, 2013

We are pleased to announce that ABB has now launched a new, dedicated in-situ reaction monitor for research laboratories and pilot plants in the chemical, petrochemical, pharmaceutical and biopharmaceutical industries.

The all new MB-Rx reaction monitor features a rugged Hastelloy ATR probe and an intuitive software interface, offering a fast and flexible solution for setting up a wide variety of experiment templates.

Providing a powerful tool for operators looking to obtain a real-time insight into chemical reaction dynamics, the innovative MB-Rx enables key parameters such as kinetics over different phases, reagent consumption and the synthesis of products and by-products to be assessed in real time.

Compact and easy to install, the MB-Rx can also be fitted inside crowded fumehoods, providing convenient access to reactors. A major benefit of the MB-Rx is its virtually maintenance-free design. Permanently aligned optics and a light source with an average lifespan of 10 years mean that the MB-Rx requires little servicing throughout its operational life, providing extended uptime and reducing the cost of ownership.

Further savings can also be achieved through the elimination of any consumables. The MB-Rx uses no hygroscopic optics or a cryogenic detector, ruling out the need for optical purging, desiccant cartridges, liquid nitrogen or Stirling coolers.

The MB-Rx reaction monitor is just part of our wider offering of process, emissions & laboratory analyzer products and systems for real-time analysis of the chemical composition and/or physical properties of a process sample or stream.

For more information about the new MB-Rx reaction monitor, please email moreinstrumentation@gb.abb.com or call 0870 600 6122 ref. ‘MB-Rx’.

Innovative water management strategies call for technologies to match

April 15, 2013

A quick look at the edie.net web site reveals an array of new initiatives and strategies from a diverse range of organisations aimed at safeguarding both the quantity and quality of water.

One thing that is clear is that there is a growing understanding of the urgent need to tackle water supply issues today before they escalate out of hand tomorrow.
Leading the way is the European Commission’s water efficiency blueprint, which calls for member states, including the UK, to step up their efforts in key areas such as pollution control and abstraction and to strike a better balance between supply and demand.

These same sentiments are repeated at an industry level, with the food and beverage industry in particular striving for improved water efficiency performance. As a major consumer of water, food and beverage companies are increasingly signing up to schemes to measure and reduce their usage. The Federation House Commitment (FHC), for example, aims to help reduce overall water usage across the Food and Drink sector by 20% by the year 2020. Sainsbury’s, Coca-Cola Enterprises, Sunlight and Branston have also all recently been awarded the Carbon Trust’s Water Standard, the world’s first international award aimed at getting businesses to measure, manage and reduce their water usage.

The Carbon Trust’s scheme also addresses the link between water wastage and energy, both in terms of consumption and carbon dioxide emissions. Every drop lost, whether it be on an industrial site or across a water distribution network, needs to be replaced, consuming extra energy for treatment and pumping.

For this innovative thinking to have maximum impact, there needs to be an equal stride forward in technological innovation.

Where water is concerned, measurement is no longer just the responsibility of the major water operators, but any major user of water too. Whether it’s to trace leakage on site, reduce water consumption or ensure compliance with emissions legislation such as the Environmental Permitting Regulations, end users should make sure they are using the Best Available Techniques for the job.

Equipment manufacturers, ABB included, are facing a growing responsibility to not only provide technology, but also to inform the market about why it is needed. By keeping an eye both on current developments and on likely future changes, manufacturers can play a valuable role in providing the technologies needed to meet both today’s and tomorrow’s challenges.

To find out more, visit our AMPPlus portal (www.edie.net/abb).