Fachbeitrag Safety to the power of three

On hearing the keyword safety, what is the first thing a person with responsibility for production thinks about in the large-scale chemical and petrochemical industry or in the oil and gas sector? The man on the street most likely assumes he would think of explosions and the subsequent fires. Or the contrary, he might assume he thinks of explosion protection - because anybody with responsibility for production is less likely to focus on the worst-case scenario but rather on its prevention. It is a fact that essential plant components operated in the industrial sectors named above are located in hazardous areas in which explosion protection is mandatory - and it is also a fact that the components and systems deployed in those areas must have the corresponding approvals. There are two further safety aspects that plant managers in those sectors should also treat with at least the same level of importance: First, the topic of functional safety; meaning the design of their plant and systems according to SIL (Safety Integrity Level) requirements. And second, the topic of lighting and surge protection. According to Arnd Schepmann, Global Industry Manager Process at Weidmüller, the industry still has a lot of ground to make up in both aspects. Mr. Schepmann is able to thank his three years experience working for Weidmüller in the USA and in particular in the oil and gas market in Texas for his knowledge of processing solutions: In the meantime he has also gained an insight into the emerging nations, where huge industrial chemical complexes and petrochemical plants have sprung up out of nowhere. „On the topic of emergency shutdown systems there are a lot of plants in those countries with an urgent need for improvement“, Mr. Schepmann reports. Functional safety was not on the agenda there for many years. However, the industry manager observes that things are now also changing in very many companies in those countries „Safeguarding human health and protecting the environment are becoming increasingly important.“ To ensure adequate protection of plant and systems in the event of an accident plant operators are required to assess the corresponding risks in a first step and then minimize them in a second. For this purpose the series of standards used in the process industry such as DIN EN 61511 define four safety levels: from SIL 1 for risks assessed as low through to SIL 4 when failure can have potentially grave consequences for the environment. The higher the risk classification the more reliable the measures must be to reduce the risk. The same also applies to operating individual devices. „With SIL 3 certified safety relays and surge protection components we offer solutions with high levels of safety functionality“, explains Mr. Schepmann. He readily acknowledges that SIL certified products are relatively new to Weidmüller‘s portfolio. This fundamentally embraces solutions for signal connections between measuring devices, actuators and controls as well as for distributed control systems. The programme includes signal converters, lighting and surge protection components for measurement and control signals as well as marshalling terminals that additionally feature integrated shield and earth connections. It is possible to deploy these in standard control circuits, in safety control circuits and also, thanks to Ex approval, in intrinsically safe measurement circuits. Thus, utilizing Weidmüller products makes it possible to achieve safety across all three dimensions: combining SIL - Ex protection - surge protection. „What is the point of determining the safety integrity level of a control circuit,“ Mr. Schepmann makes clear, „if the safety-related signals fail anyway as the result of a lightning strike?“ All three signal circuits are protected against surge voltages by products from the Varitector range: VSPC, approved for SIL 2 and SIL 3, are designed for use in standard and safety control circuits, the blue VSPC Ex version in intrinsically safe signal circuits. What‘s more, with its Varitector SSC Ex the manufacturer based in Detmold, Germany, offers lightning and surge protection products housed in a 6 mm terminal format, which is both compact and space saving by design. That means they can be simply installed in a marshalling cabinet in place of a terminal block. Mr. Schepmann announced further relay products will be introduced in time for the Achema trade fair. „Marshalling distributors and, as a consequence, SIL relays are increasingly being deployed in the area close to the process“, the industry manager explains. „There they face harsh environments, such as vapours bearing sulphuric acid.“ This is when products with an integrated PCB need to be particularly well protected. Here Weidmüller confidently relies on a so-called G3 coating, a requirement emanating from the American market. This protects the electronics against corrosion. „That means in future our relays can also be utilized in harsh environments, such as offshore platforms.“ The highlight will undoubtedly be the safety relay SCS 24 VDC SIL 3, a Safeseries module. Utilizing this module guarantees emergency shutdown of plant and plant components. In addition to a safety circuit it is also equipped with a monitoring circuit with a wide-range voltage input. Mr. Schepmann explains the background „That is often a significant aspect in safety systems in particular, because the interaction with backup systems requires an emergency power supply - and that often means a different voltage to that supplied via the mains.“ Other features of the new safety relay are two yellow LEDs, which simplify fault analysis of both circuits (relay output and monitoring). Three relays are connected in series in the output of the SIL circuit. This circuit arrangement guarantees reliable isolation. The typical break time is about 14 and the make time 7 ms. In addition, the safety circuit is immune to test pulses, which are usually used in distributed control systems (DCS) to monitor the status of the signal circuits. The relay is designed for use in temperatures ranging from -25 °C to +50 °C. Does this make Weidmüller a complete end-to-end supplier? Mr. Schepmann says not, „There are still niche products that we do not offer - for example in the field of safety for the process industry. We are an innovative provider of industrial connectivity solutions for instrumentation and control technology (PLC (DCS marshalling)) as well as field wiring in hazardous area applications. Our broad spectrum of products, including for the non-Ex field of standard signal transmissions, means we are able to fulfil the most diverse of requirements for the customer operating in the signal transmissions industry.“ Because at the end of the day the customer still needs standard equipment for SIL and Ex protection applications such as for electrical cabinets, power supplies, terminal blocks, markers and much more. Not even the absolute safety specialists offer or come close to offering anything like as complete an assortment as Weidmüller. „Moreover“, according to Mr. Schepmann, „the SIL certified product and the signal circuit fulfilling safety design requirements alone are of little use if other influencing factors interrupt the signal circuit.“ For instance, a corroded connection somewhere - after all it is not possible to certify the connection technology itself to SIL. „However, we do ensure that it is insensitive to environmental conditions.“ That applies to the wiring just as much as to the electronics; both are required to fulfil a very high standard of quality. In this respect Weidmüller simply does not compromise - beginning with the manufacturer‘s stainless steel enclosures �??Made in Germany‘. „SIL is a single component of a holistic view of safety“, Arnd Schepmann asserts. That applies in particular in the process industry: Because for that industry and its users the golden rule at all times is: no compromises.