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?