Checking and grounding

When a company wishes to use Type C bags its must provide a means for grounding the bag . This can be achieved with either passive ( single pole clamp and cable ) or active means ( monitoring systems ), but given the scale of the charge that can build up on bags and the resulting energies that can be reached by static sparks , in combination with the presence of a combustible dust cloud , an active grounding system is the better choice . This is because the system can determine whether or not the bag ’ s construction complies with the recommendations of the standards highlighted above and will also ensure the bag is grounded for the duration of the filling / emptying operation . The primary benefit of

Figure 1 checking the resistance through the bag is to ensure that after many cycles of repeated use , the static dissipative threads are functioning correctly and , more importantly , to ensure that bags not of Type C construction are not permitted to be used in the hazardous area . Additional benefits with grounding systems are that they can control the movement of the powder through output contacts interlocked with valves or PLCs . Fig 1 highlights how a bag can be checked for its static dissipative capability in combination with providing active grounding of the bag . Following the connection of two quick release clamps , the Earth-Rite FIBC system will identify if the bag is operating in accordance with the relevant standard . This is achieved by sending an Intrinsically Safe ( Hazloc approved ) signal ( red line in the illustration ) through the bag . If the green ground status indicators pulse continuously , the operators know the bag is grounded . The system verifies the grounding of the bag by ensuring the signal returns via a verified true earth ground . If there is any charge on the bag it will leave the bag via the static dissipative threads to the verified ground . If the output contacts are interlocked with the process then the material cannot flow without the permission of the operator .

10 or 100 meg-ohm ?

The primary question to address when selecting a Type C FIBC grounding system is to determine which standard the bags in use are constructed to . Although bags manufactured in accordance with the 10 meg-ohm requirement are growing in number , there is a significant percentage of Type C FIBCs manufactured in accordance with the 100 meg-ohm requirement . If the company is committed to using CENELEC compliant 100 meg-ohm Type C bags then the grounding system should monitor the full range of resistance . This ensures that bags of different static dissipative consistency can be checked and monitored for the full permissive range of resistance . Any bags operating outside of this range should be rejected . Likewise , if a company is committed to using IEC / NFPA 77 compliant 10 meg-ohm bags the permissive range of resistance to which the grounding system should be monitoring should be 0 ohms up to 10 meg-ohms .

Bag specific

If a grounding system is selected that monitors a narrow range of resistance , for example , monitors from 0 ohms up to 50 meg-ohms , this creates a problem and this problem could have two outcomes ( Fig 2 ). The first is that if 10 meg-ohm bags are specified for the site , the system could pass faulty bags as it will pass any bag that shows a resistance from 10 meg-ohms up to 50 meg-ohms . A direct consequence of this feature is that it could be passing bags not manufactured in accordance with IEC-61340-4-4 and the recommendations of NFPA77 . The second outcome is if 100 meg-ohm bags are specified for the site . As the grounding system has a cut-off resistance of 50 megohms , it will fail any bag that is operating between 50 megohms and 100 meg-ohms . A direct consequence of this problem is

Figure 2

that the system could reject a bag that is perfectly adequate and result in delayed operations while the operators are replacing the bag . It is , therefore , of paramount importance to determine what types of Type C bags the site will be using . On that basis the site can select a system that will monitor the full range of 10 meg-ohm bags or a select a system that will monitor the full range of 100 meg-ohm bags .

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• Ensure Type C bags are manufactured in accordance with the electrostatic recommendations of IEC 61340-4-4 / NFPA 77 or CLC / TR : 50404 .

• Ensure that the grounding system selected can check and continuously monitor the full range of resistance through the bag .

• Ensure the grounding system not only checks the condition of the bag ’ s static dissipative threads , but also ensure that the ground circuit includes a direct and monitored connection to a verified True Earth grounding point .

• Ensure the grounding system does not monitor a limited percentage of the permitted range of resistance as they may pass faulty bags and reject acceptable bags .

Technik introduced a newly designed tank bottom valve system : a ball-valve technology-based PFA lined foot valve completed with the NKS-T lined butterfly valve and a new PFA lined 3ins BSP outlet flange . Based on Richter ’ s own technology , the tank bottom valve system reduces total cost of ownership while increasing safety and efficiency for operators of tank containers , the company says . Richter ’ s ball-valve technology eliminates the possibility of damaging the internal coating with opening and closing of the valve which eventually leads to corrosion . Furthermore , the TE / F valve is equipped with up to seven times thicker PFA coating , a material which delivers better performance on typical chemical resistance compared to current ECTFE solutions . Richter ’ s ball and butterfly valves have proven to last up to more than a decade in the most extreme conditions . Real world examples of over 900,000 opening and closing cycles of Richter ’ s PFA / PTFE lined NK series butterfly valves are not uncommon . The typical ‘ emergency closing mechanism ’ ( steel wire ) offers no option for the operators to open the ‘ last line of defence ’ outside the danger zone . With the safety of the operator in mind , Richter has replaced this ‘ remote control ’ with a robust stainless steel bar system for closing and opening at a safe distance to ensure the operator will not be in harm ’ s way with either of these two procedures . The TE / F valve features Richter ’ s Labyrinth seal and Envipack technology , which adds to the total concept of a robust design combined with great performance . The NKS-T butterfly valve which is based on the successful NKS series of butterfly valves was developed to fit perfectly with the TE / F tank bottom valve . To complete the offering a new-to-market PFA lined 3ins BSP flange with end cap was developed to assure total integrity of the system . “ The TE / F was developed out of a direct operator need across the tank container industry to reduce operating costs ,” said Keshwar Anroedh , director marketing & product management . “ We ’ re proud to supply the logistics industry with innovative solutions that will provide increased safety , along with better performance and increased lifetime ,” he continued . Richter ’ s TE / F tank bottom valve and NKS-T butterfly valve are available in DN80 ( 3ins ) and are well-suited for lined tank containers transporting corrosive or high purity media . This is just another example of Richter ’ s solution focused innovative engineering by simply listening to the end user .