Hazard identification 1 Introduction n A Hazard and
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Hazard identification 1
Introduction n A Hazard and Operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation. n n The HAZOP technique was initially developed to analyse chemical process systems, but has later been extended to other types of systems and also to complex operations and to software systems. With respect to maintenance, the HAZOP method could be applied with the following objective: 2
HAZOP objective n Analysis of the technical system in order to find weak points where a maintenance task could reduce the probability of failure, and/or the consequence of a failure n Analysis of the maintenance action (procedure HAZOP) where the objective is to identify critical tasks when executing the maintenance. 3
HAZOP procedure 1. Divide the system into sections (i. e. , reactor, storage) 2. Choose a study node 3. Describe the design intent 4. Select a process parameter 5. Apply a guide-word 6. Determine cause(s) 7. Evaluate consequences/problems 8. Recommend action: What? When? Who? 9. Record information 10. Repeat procedure (from step 2) 4
HAZOP process parameters Flow Composition p. H Pressure Addition Sequence Temperature Separation Signal Mixing Time Start/stop Stirring Phase Operate Transfer Speed Maintain Level Particle size Services Viscosity Measure Communication Reaction Control 5
Study node n A study node could be a line, a vessel, a pump, or an operating instruction 6
Guide words Guide word No (not, none) More (more of, higher) Less (less of, lower) As well as (more than) Part of Reverse Other than (other) Early / late Before / after Faster / slower Where else Meaning None of the design intent is achieved Quantitative increase in a parameter Quantitative decrease in a parameter An additional activity occurs Example No flow when production is expected Higher temperature than designed Lower pressure than normal Other valves closed at the same time Only some of the design intention Only part of the system is shut is achieved down Logical opposite of the design Back-flow when the system intention shuts down Complete substitution – another Liquids in the gas piping activity takes place The timing is different from the The valve is opened to late intention The step (or part of it) is effected The work starts before the high out of sequence voltage is disconnected The step is done/not done with Oil is removed faster than the right timing sink can swallow Applicable for flows, 7 transfer, The fluid is emptied in the wrong sources and destinations bottle
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Example of HAZOP worksheet for the process parameter flow GW Deviation Consequences Causes No No flow Too much 1. ammonia in the reactor. Discharge 2. to working area 3. Less Les flow More flow Recommend action Valve A fails in closed position Phosphoric acid depot is empty Pipe blockage, or pipe fractured Too much 1. Valve A partly closed ammonia in the 2. Pipe partly blocked, reactor. Discharge or fractured to working area. Investigate the situation! Automatic closure of valve B when no flow from phosphoric depot Too much phosphoric acid. No danger in working area 9 Automatic closure of valve B when flow is missing or is reduced from phosphoric depot Set-point determined by toxicity and flow limitations