Safety Isolations Overview - Intergraph Smart Completions - 5.3.6 - Help - Hexagon PPM

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5.3.6

A Safety Isolation Procedure (also called Lockout/Tagout) is a critical safety document required for the control of hazardous energy and substances while servicing and/or accessing machinery and equipment. This manual is intended to provide a guideline on how the de-energization of a system is approached and will also help identify proper isolation points. In addition, this manual discusses how the pre‐defined isolation points are entered into Industrial Business Solutions Safety Isolation Manager (SIM) software and how the SIM manages a variety of aspects to ensure only accurate and up-to-date Safety Isolation Procedures are accessed for use.

CATEGORIES OF ENERGY

There are three broad categories of energy that pertain to the safe isolation of equipment or systems; active energy, stored energy and process energy. Further breakdowns of these categories are listed below:

Active Energy Sources:

  • Electrical

  • Mechanical

  • Pneumatic

  • Thermal

  • Hydraulic

Stored Energy Sources:

  • Capacitors

  • Springs

  • Compressed gas, air, steam, water etc.

  • Elevated machine members (potential energy)

  • Rotating flywheels

  • Hydraulic systems

Process Energy Sources:

  • Chemical drains

  • Oxygen, nitrogen, hydrogen

  • Hydrocarbons or other flammable substances

  • Caustics, acids or other corrosives

  • Toxic vapors, fumes, liquids, gases or dust

  • Radiation sources

ANALYSIS OF SYSTEM DE-ENERGIZATION

The example task will be a maintenance inspection of agitator blade 100-AG-010 that is used in tank 100-TK-010. There are 5 fundamental steps for proper de-energization of a system:

  • Understand the system

  • Stop the system

  • Remove or isolate hazardous substances

  • De‐energize the system

  • Verify "zero energy state"

System Description

The system presented below is a mixing circuit with a recirculation line back from the feed pump. Process make‐up containing suspended solids is added to the tank based on desired level. The level in the tank is measured using a level element LE‐202, which transmits the signal to the control system where it is compared with a set‐point controller LIC‐202. Depending on the process variable with the set point, the flow control valve FV-202 is manipulated to meet the desired set point. It is normal practice to have manual isolation valves (HV‐501 and HV‐502) around a flow control valve to allow for repair or replacement. The tank features a motorized agitator 100‐AG‐010 used to keep the solution well mixed. The solution is pumped from the tank using a centrifugal pump 100‐PP‐202 at a constant rate. The solution is sent to the downstream process based on requirements entered into the flow controller FIC‐001. This flow controller subsequently manipulates a flow control valve FV‐001. Excess solution is re‐circulated back to the tank. There are two drain valves on this system. A manual drain valve HV‐401 that is normally closed to allow draining of the tank. There is also a manual drain valve on the discharge line of the centrifugal pump HV‐402. This is to allow drainage of any standing solution in the line.

Stop the System

The system would be typically stopped from the control room. The system could also be stopped locally in the field if designed as such. Given the system described in Section 3.2.1, the following items must be shut down to bring the system to a full stop:

  • The makeup level controller LIC‐202 would be put into manual mode and the output set to zero to completely close the valve

  • The process pump PP‐202 would be stopped

  • The process flow controller FIC‐001 would be put into manual mode and the output set to zero to completely close the control valve.

  • The agitator 100‐AG‐010 would be stopped

Remove or Isolate Hazardous Substances

The task required is to inspect and perform maintenance on the agitator. Therefore, access inside the tank is necessary and the tank must be drained. Furthermore, there is a recirculation line that should be drained as well because any positive pressure placed in the line could force any remaining solution into the tank. This valve should also remain open in the event that backflow were to occur.

Drain the tank using HV‐401

Drain the recirculation line using HV‐402 and lock the valve open

De-Energize the System

There are two energy sources that must be de‐energized in this system. Mechanical energy from the agitator and process energy from the make‐up line, potential back flow from the process line and from the process pump:

  • The breaker must be opened for agitator 100‐AG‐010 in the motor control center (MCC) breaking the electrical connection. A lock and tag must be placed on the breaker.

  • The breaker must be opened for process pump 100‐PP‐202 in the motor control center (MCC) breaking the electrical connection. A lock and tag must be placed on the breaker.

  • Manual valve HV‐501 on the make‐up line, must be closed, locked and tagged. A tag must also be placed on the valve indicating that it has been isolated.

  • Manual valve HV‐504 on the process line, must be closed, locked and tagged. A tag must also be placed on the valve indicating that it has been isolated.

Verification

The last but most important step in safety isolations is to verify that the equipment or system is not operable. Verification should be performed from the local control panel as well as the central control room. The equipment selector switch is put into "Local" mode and a start initiated from the field to verify that the equipment will not start. The equipment is then switched to "Remote" mode and a start is attempted from the control room. Field verification that the equipment will not start is required. The selector switch is then set back to "Local" while the equipment is being accessed.

The steps outlined above relate only to de‐energizing the system. There may be other safety issues that require attention prior to accessing the system such as confined space entry permitting, removing hazardous process materials or scaffolding procedures. These items must be identified and incorporated into the isolation procedure. However, discussion of these other issues is beyond the scope of this document.