The Logic Behind The Magic. “Shut Down Valve".

The isolation of sections of plant will typically be an engineering judgement based on:
1. The purpose for the isolation; either maintenance/operation or shutdown
2. The design condition of the section, particularly pressure
3. The nature of the fluid in the section, e.g. flammability, toxicity etc

Isolation of a section for shutdown purpose will always consist of a single, actuated valves on the perimeter, which will respond to a shutdown signal(s) from ESD systems. Single shutdown valves are normally sufficient for the event initiating the shutdown and associated risk

The Logic Behind The Magic. “Smoke and Heat Detectors"

There are two types of smoke detectors, each having different applications

Ionization Smoke Detectors detect the presence of smoke by means of a small ionization chamber and a source of ionizing radiation. Ionization Smoke Detectors are generally better at detecting smaller smoke particles such as that produced by rapidly burning fires, but are less sensitive to the larger smoke particles generated by smouldering fires, etc.

Photoelectric (Optical Point) Smoke Detectors detect the presence of smoke by means of a small light source and a separate photoelectric light sensitive cell housed within a sensing chamber. Photoelectric Smoke Detectors are generally more sensitive to larger smoke particles such as that generated by dense smoke or smouldering fires, but are less sensitive to small particles of smoke found in rapidly burning fires.

The Logic Behind The Magic. “Open Path Type Gas detector”

Open Path type gas detector devices measure the sum of the hydrocarbon molecules along a narrow beam, the configuration for displaying the reading from an IR beam gas detector is as follows:

Display in LEL-meters which is an integral of percentage LEL as multiplied by the length of the beam.  This is in effect a direct reading of what the device is measuring i.e. the total number of hydrocarbon molecules along the length of the beam.

Alarm levels should be set at a low level but such that spurious alarms are avoided, typically:

·         High level gas – 1 LEL.m,

·         High-High level gas – 2.53 LEL.m 

The Logic Behind The Magic. “IR Flame Detectors" The Logic Behind The Magic. “IR Flame Detector”. ”.

Fire detection is required for process equipment and heat generating utilities, specifically where liquid hydrocarbons may accumulate.  For areas where there is a significant fire risk, additional detectors employing diverse techniques may be considered.

The fire detectors should be selected to suit the conditions and to provide the earliest reliable warning. The suitability of the fire detector is dependant upon the characteristics of the fire, which are determined by the materials involved and their rate of combustion.

Triple Band IR Flame Detectors are considered best practice for flame detection.

Sample of IR Flame Detectors criteria and requirement is shown below.

The Logic Behind The Magic. “Hydrogen Sulphide detectors”

Fixed toxic gas detection is usually provided throughout the platforms due to the significant levels of H₂S in the process fluids being handled and the need to ensure the rapid detection of H₂S gas hazards to warn personnel.

Electrochemical type is widely used and installed in areas where the accumulation of H₂S is likely and at all ventilation intakes

High or High High gas detection by a single H₂S gas detector shall only initiate alarms whereas a coincident High High gas detection by two or more detectors shall initiate a confirmed gas condition with subsequent actions in accordance with F & G Cause & Effect Matrix.

The Logic Behind The Magic. “Gas detector”.

Gas detectors is installed in the platform according to the type and nature of perceived hazard. For example, IR point type gas detector only measure flammable gas concentrations at certain points and there is no way of knowing the composition of the gas cloud between the point detectors, it is therefore necessary to initiate alarms and executive actions well before the concentration at any point reaches 100% of the LFL. The settings shall be as follows:

·         High level gas (process areas) – 20%LEL,

·         High-High level gas (process areas) – 50%LEL,

These type of detector usually have 7 signals and status that are shown in the control room,

1. Faulty Status
2. Calibrate alarm
3. High gas alarm
4. High  gas exec action
5. High-high alarm
6. High-high gas exec action.
7. Inhibit signal

Pipe Reducing Factor

Holden wants to install 1" valve in 2" size pipe. But he wonder what are the reducing factor that he needs to consider. So he began to make the calculation.


Cv with piping geometric factor consideration equations are:



         
             Where Fp (R)

 

Where:

 d :           Valve inlet diameter 

D            :           Internal diameter of the pipe 

K            :           Head loss coefficient of a device, dimensionless

N2           :           constant to suit the measurement unit, 890