A variety of instrument problems
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1. The criteria for determining explosion-proof zone classification seem rather vague. For a new project, in the absence of design work by a design institute, on what basis can the internal instrumentation staff determine whether flammable gases will be present in that area on a long-term basis? How many hours per year are combustible gases present? Which district should it belong to? 2. If a workshop is classified as Zone 1 and explosion protection ratings of ExdIICT3 are selected for temperature, pressure, etc., then without installing partitions in the cable trays or using safety barriers or intrinsically safe cables, cannot other instruments such as valve positioners use intrinsically safe versions? Do we have to choose other instrument brands with an explosion-proof rating? If intrinsically safe instruments are also used for instruments such as those for temperature and pressure, but only flameproof flowmeters are available, can they still be used? 3. If a workshop is classified as Zone 0 and the production material is hydrogen, can explosion-proof flexible hoses be used? (After online research, it is found that explosion-proof flexible hoses are suitable for Zones 1 and 2, as well as for explosive gas environments of categories IIA and IIB.) If they cannot be used, what should be chosen instead? If it is Zone 1, in the presence of hydrogen, explosion-proof flexible hoses are only suitable for Class IIA and IIB explosive gas environments – can they be used in such cases? One of our factory’s production workshops uses explosion-proof flexible pipe connections designed by the design institute in the presence of hydrogen – is this appropriate? 4. Is the cost of intrinsically safe instruments combined with intrinsically safe cables and safety barriers significantly different from the cost of flameproof instruments combined with ordinary cables? 5. When installing online monitoring instruments such as pH and ORP in explosion-proof areas, if a Mettler Toledo pH meter is chosen, how should it be installed to comply with the installation specifications? Should an explosion-proof box be used? 6. During production, the steam pressure and temperature experience significant fluctuations; the pressure varies between 0.4–0.5 Mpa, while the temperature ranges from 170–180 degrees Celsius. If a orifice plate flow meter is to be ordered for measuring steam flow, how should the temperature and pressure parameters be specified? 7. For measuring the flow rate of hydrogen gas, when using an orifice plate flow meter versus a thermal mass flow meter, is there a significant difference in their accuracies? Does a orifice plate flow meter necessarily need to go through a flow integrator before it can be connected to the DCS? And since a thermal mass flow meter has built-in temperature and pressure compensation, can it be connected directly to the DCS without a flow integrator? Is there a large price difference between two flowmeters of the same caliber?
So many problems: lol, for reference only. 1. To determine whether a particular area is prone to the presence of flammable gases over the long term, it is possible to analyze this by examining the process flow and the Safety Data Sheets (SDS) of the chemical substances involved. It is necessary to evaluate the equipment and operational processes that may release flammable gases. 2. If the workshop is classified as Zone 1 and sensors with an ExdIICT3 explosion protection rating are used, then instrumentation equipment with the same explosion protection rating as the temperature and pressure sensors should be used. It is also acceptable if only the flow meter is of the flameproof type; however, the explosion-proof rating of the entire system must remain consistent. 3. Explosion-proof flexible hoses cannot be used in a hydrogen environment in Zone 0. In such an environment, pipes made of materials and designed for Zone 0 and suitable for hydrogen safety should be selected. In cases where Zone 1 contains hydrogen, it is not recommended to use Type IIA or IIB explosion-proof flexible conduits; instead, products suitable for this specific environment should be selected. 4. The cost of intrinsically safe instruments combined with intrinsically safe cables and safety barriers differs from the cost of flameproof instruments combined with ordinary cables; the specific difference depends on the specifications and brand of the equipment chosen. Typically, the initial investment for intrinsic safety systems is high, but the maintenance costs are low. 5. When installing PH or ORP online monitoring instruments, appropriate explosion-proof measures must be selected in accordance with the on-site explosion-proof requirements. When using a METTLER TOLEDO pH meter, it is advisable to use an explosion-proof box or a housing that meets the corresponding explosion-proof rating. 6. When ordering orifice plate flow meters, the average temperature and pressure range should be specified, namely a temperature of 170–180 degrees Celsius and a pressure of 0.4–0.5 Mpa. These parameters are applied to the design and calibration of flowmeters. 7. In the measurement of hydrogen gas flow rate, thermal mass flow meters are generally more accurate than orifice plate flow meters, as they directly measure mass flow and come equipped with temperature and pressure compensation. The orifice plate flow meter outputs a differential pressure signal, which needs to be converted into a flow signal using a flow integrator before it can be fed into the DCS. There will be a price difference between the two, depending on the technology and manufacturer chosen.
There’s not even a design yet, and you’re still thinking about such detailed things – that’s tough for you :)
May I ask which standard states that explosion-proof wire glands cannot be used in Zone 0? I also have a question: if intrinsically safe instruments together with safety barriers are used to form a safe circuit, then why cannot explosion-proof wire glands be used?
Thank you for your detailed explanation! I have another question regarding the second point: if I use explosion-proof instruments with an ExdIICT3 rating for both temperature and pressure measurement, then can’t I use the Yamawa AVP100-H for my valve positioner? (The manual states that only intrinsically safe models are available; this type of positioner is used in other workshops at our factory, and I have quite confidence in it.)
A fool, with a thousand attempts, will surely find success once! :Lol, I have nothing to do, so I’m just guessing around! :handshake