Pressure Safety Valve (PSV) Material Selection

Specify the Pressure Safety Valve (PSV) material could be simple and might be difficult for some situation. It becomes simple because the API 526 only state the requirement of the body, bonnet, and spring material. Nevertheless, the API 526 standard leave the internal part material to the manufacturer’s standards. If the project requirement or Company standard require the material of the PSV shall follow the API 526, then the material selection of the PSV is simple. Just specify the body/bonnet material of the PSV in accordance with the related PIPING globe valves and leave the other parts to manufacturer’s standard. It means, we need to know the piping class of our PSV, see the globe valve code number for the specified piping class, and then open the manual valve datasheet of the globe valve. We will then just simply state the disc, guide, nozzle, etc, to become manufacturer’s standards.

Valves Material Comparison

During vendor bids evaluation of the valve package, usually we will face the problem of material review from the Vendor offer. Let’s say we require a valve with A182 F53 Duplex stainless steel trim material, but the Vendor offer different material such as A182 F51 Duplex stainless steel. To accept or not this Vendor offer will be a problematic issue for an instrument engineer. In this case, just contact the material engineer and ask them whether vendor offer is acceptable or not.

However, as a general guideline, the following table could be used just to compare the superiority of one material to other material. Use the table with below notes as a general guideline.

Fire & Gas Detection Philosophy Part 1: Fire Detection

Fire Detection

In general, the fire detection system shall have the following objectives:

-          To detect fire in very early stage of it’s form.

-          To alert operator at control room and give them the location.

-          To alert any personnel at location of the fire event so that they are aware and could take any necessary action.

-          To activate the fire fighting equipment.

Sheath Material of Instrument Cables

Sheath of the instrument cables are used to protect the cables from damage. The material of the instrument cable sheath (inner and outer) shall be selected as per operating temperature of the cable.

The material shall be one of those listed in IEC 60092-359. The sheath material are divided in to two category, thermoplastic and elastomeric or thermosetting material. Each of them has halogen free option i.e. thermoplastic halogen free or thermosetting halogen free.

Recommended Instrumentation Cables Construction for Offshore Oil and Gas Industries

Typical Instrumentation Cable Construction for Offshore

Instrument Power Cable Sizing Part 2: The Simplified Equations

At actual application we rarely know the resistance of our equipment. What usually specified by manufacturer is only a power consumption at nominal power supply (can be 24 VDC or 48 VDC). So, how to get the equation to calculate the voltage drop across some distance with using the power consumption data?

Instrument Power Cable Sizing Part 1: The Basics

Note: due to blogger limitation, the symbol ohm and delta couldn’t shown here, as a replacement it is shown as OHM and Delta.

What is an instrument power cable sizing? Instrument power cable sizing is a calculation of voltage drop across some distance from instrument marshalling cabinet to field devices. It is needed to make sure that the supply voltage at the field devices is sufficient (within device operating voltage or within specified requirement). For example, we have a solenoid valve put at 250 meter from marshalling cabinet. This solenoid valve requires a supply voltage 24 VDC. Due to a long distance separated, the voltage received at solenoid valve will not be 24 VDC. It may be 23.5 VDC, 22 VDC, or even 15 VDC. It depends on the size of cables that used. So, the purpose of the instrument power cable sizing is to select the appropriate cable size so that the voltage drop received at field devices is within an acceptable range or within specified requirements. So, how to perform such calculation?

Typical Calibration Procedure of Displacer (Buoyancy) Level Transmitter

Operating Principle

The displacer level transmitter (or any other buoyancy level transmitter) uses the effect of buoyancy. When the displacer is immersed in the process fluid, this buoyancy effect will make the displacer lighter than the non immersed displacer. This change of displacer weight is then detected by the sensor (whether use torque tube or LVDT) and then translated as a fluid level.

2 Wires, 3 Wires, or 4 Wires RTD (Resistance Temperature Detector)?

RTD is a temperature sensitive metal. The resistance of the RTD metal is gradually changed with the changed of temperature. In applications there are 2 wires, 3 wires, and 4 wires RTD. 2 wires RTD means that the RTD only connected to the transmitter by using 2 wires, 3 wires means its connected by 3 wire and 4 wire means its connected by 4 wires. So what it should be, 2 wires, 3 wires, or 4 wires RTD?

The Difference Between API and ASME Pressure Safety Valve (PSV)

In the vendor data sheet, calculation sheet, and or catalogue of the PSV, it was stated two different terms which is API and ASME PSV that usually makes confusion to a young engineer. Some times it is stated as API area, ASME area, actual area, etc. So actually what is the difference between this API and ASME pressure safety valve (PSV)?

Flow Direction of Control Valves

Flow direction of control valves has a relationship with a failure action, High Delta Pressure, Cavitation, and % opening of the valve. There are 2 type of control valve flow direction: Flow to Open (FTO, or Tending to Open), Flow to Close (FTC, or Tending to Close).

Marshalling Cabinet or Marshalling Panel

As discussed in the Typical Architecture of Instrumentation and Automation System, the automation architecture of the plant is having a marshalling cabinet in between the junction box and the system cabinet.  This marshalling cabinet function is to interface the incoming field cable (which is normally a multipair cable) and the I/O (Input/Output) card connection. Without marshalling cabinet, we can sure (for large number of I/O) that there will be a trouble for operation personnel to maintain and operate the cabling.

Typical Architecture of Instrumentation & Automation System

In general application, the instrumentation and automation architecture is consist of field instruments, individual & multicore cable, junction boxes, marshalling cabinet, and system cabinet. Each of them is combined together so that the control loop application can be performed correctly.

End Connection of Control Valves

The control valve end connection may have flange connection, threaded, or even welded end. Flange connection is the most common control valve end connection in the oil & gas application. Other connection such as threaded or welded end is only used in particular application.

MOV ~ Motor Operated Valves

Motor operated valve (MOV) is an ordinary ball valve or any other valve that operated by an electric actuator. In general, the MOV is used as isolation valves for equipment which requires regular access. The MOV is also used on any valve that the total energy required to open or close the valve manually is large. No specific reason regarding why MOV is used except from ease of operation point of view.

Instrument Engineer Expertise

A. Instrument Specifications

- Gas/Condensate/Oil Metering Specification

 - Automation System Network Spec

 - Control Panel, Cabinet and Rack Specification

Valve Manifold for Pressure Transmitter

Valve manifold is a standard accessory for pressure transmitter and differential pressure transmitter. By providing a valve manifold in the instrument, it will allow a calibration or change the instrument without the necessity of plant shutdown. In particular application there are three type of valve manifold, 2-way valve manifold, 3-way valve manifold, and 5-way valve manifold.

Control Valve Trim

As per ISA S-7505 trim is defined as the internal parts of a valve which are in flowing contact with the controlled fluid. Usually it contains a plug, seat, & stem. The body & bonnet of a valve isn’t considered as part of the trim. Valve trim could be in the several types. The classification by valve manufacturer can be as per seat material used, trim function, and guided used.

Wellhead Control Panel (WHCP)

It is very common in the oil & gas plant to control its oil or gas well through a wellhead control panel (usually called WHCP). Each well is always equipped with a SCSSV (Surface Controlled Sub-surface Safety Valves) or usually it is called as down hole valve (DHV) and a SSV (Surface Safety Valves) which is consist of a Master Valves (MV) and Wing Valves (WV). SCSSV in most application is an on-off valve with hydraulic actuators. While SSV can be driven by hydraulic actuator or pneumatic actuator depends on the pressure rating. It is also a need to open or close SCSSV and SSV in sequence and accommodate an Emergency Shutdown signal from the systems. So what are WHCP and its essential component? This article tries to explain the WHCP systems in general application and how it works.

Thermowell Insertion and Immersion Length

There are two different terminologies for thermowell, one is insertion length, and another one is immersion length. Thermowell insertion length is the total unsupported length from the edge of connection (flange or threaded) up to thermowell tip. Thermowell immersion length is the total length from the tip to the point of the fluid/media immerse. Usually, for easiness, the border of the media that will immerse is the pipe or vessel wall (see below picture for illustration). The problem is how we should specify the insertion length and the immersion length of this thermowell?