InTech

MAY-JUN 2019

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INTECH MAY/JUNE 2019 35 SPECIAL SECTION between the parties, with clear tasks and a sys- tem to collect and communicate the findings. The tools used for PM tasks are either instru- ment asset management systems (IAMSs), hand- held tools, an instrument built-in keypad, hand tools, or shop activities. The frequency of a PM task is based on prior knowledge from similar equipment, manufacturer or supplier data, reli- ability data, and performance prediction, and defines the task as online or shutdown activity. Strategies to optimize PM Optimizing the preventive maintenance for instrumentation is needed to eliminate unnec- essary activities and unnecessary cost. Exces- sive preventive maintenance may also cause nuisance trips or operation upset. This is an- other motive to optimize the PM tasks. Implement optimization with the following strategies: improve the design and apply tech- nologies, capitalize on instrumentation self-diag- nostics and online condition monitoring, and use the redundancy approach, once justifiable. Design and technology Nowadays, available technologies, like smart sensors, bring a new dimension of reliability and minimize maintenance requirements. Capitaliz- ing on the following technologies and design ap- proach will highly reduce the PM scope and time: ● single-rod, guided-wave radar (GWR) for level measurement ● pressure transmitters instead of process- actuated switches ● smart pressure and vibration fork switches (with display and/or diagnostics) instead of conventional blind switches ● diaphragm/remote seal pressure transmitters instead of tubing-based transmitters ● digital vibration transmitter/switch instead of mechanical switches ● smart valve positioner ● single-rod GWR and two-wire noncontact radar for inventory tanks application ● electrochemical gas detector for H 2 S gas detection ● infrared gas detec- tor for combustible gas detection ● configuring a dis- crepancy alarm between adjacent control and safety transmitters ● avoiding soft-seat- ed control valves and instead install- ing a metal-seated control valve next to a tight shutoff rotary isolation valve Diagnostics and online condition monitoring Available instruments are now smart and have in- ternal diagnostics (analytics) and digital commu- nication. These features are effectively used to im- prove the preventive maintenance program and eliminate or highly reduce traditional practices. Diagnostic data is obtained and collected using: ● smart sensors (like smart transmitters, smart positioners, and smart pressure switches) ● an analytics data platform (IAMS, which re- ceives the data from the smart instruments via a wired or wireless connection and generates a status message with a recommendation) ● digital connectivity, like Foundation fieldbus (FF) with physical layer diagnostics Redundancy Redundancy is having a permanent or temporary reference to compare the installed instrument per- formance and reading to. Below are some examples: ● having dual circuits (or more) for axial and radial vibration, bearing temperature, and fired equipment flame monitoring ● applying two-out-of-two voting, if safe and practical, to avoid nuisance trips and reduce ex- cessive maintenance ● installing control and shutdown transmitters FAST FORWARD ● Preventive maintenance for instrumentation shall be redefined as periodical, online, or shutdown tasks. ● Achieve PM optimization by enhancing the design, effectively using instruments' built- in diagnostics, and utilizing new or alterna- tive technologies. ● Digital transformation can eliminate or greatly reduce conventional preventive maintenance for instrumentation. 1: Maintenance categories Before failure After failure 2a: Preventive maintenance 2b: Corrective maintenance 3a: Condition-based maintenance 3b: Predetermined maintenance 4a: Testing and inspection 4b: Condition monitoring 4c: Periodic test 4d: Scheduled replacement 4e: Scheduled service 4f: Immediate 4g: Deferred Figure 1. Maintenance categorization Source: ISO 14224:2016

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