In this article, you will learn how to full up instrument datasheet, pressure gauge specifications and their standards.
Step 1: Datasheet Format. Freeze the final format of the datasheet.
e.g. ISA20, Instrument Specification Forms/ Client format / Vendor format etc
Generally, the datasheet format covers the document number, title, client logo, project name, project number, revision history table, etc since every project is unique, and this document is used for the entire life cycle of the project until the plant is decommissioned.
When you look at the format of the datasheet, you will notice/realize that datasheet is sub-divided into various sections like General data, process-specific data, material / mechanical specific data, instrument-specific data, notes/ remark section, testing and inspection data, certification & standards related information, special requirements and purchasing data.
The most important thing for instrument selection is that it should be “fit for purpose”.
Step 2: General data
To fill up the general section, we need to fill in the tag number and other general information.
From the P&ID (Piping and instrumentation diagram), one can get the instrument tag number, line number & line size/equipment number, PMS (piping material specification) and service, etc
Step 3: Get the process data [This is the interface between the process and instrument engineer]
Normally process engineers provide the process data applicable for the instrument in form of an instrument process datasheet which is also called IPDS.
Process engineers provide this information based on Material & heat balance streams. Sometimes this being an interface document, the format of IPDS is aligned with the Instrument datasheet process data section.
IPDS covers fluid name, its state (Gas / Liquid / solid) and properties like corrosive / toxic / erosive
It will also cover operating conditions (minimum, normal, maximum) and design conditions of the process that is applicable for a particular instrument. Here in this example pressure gauge.
As we know for pressure measurement, the pressure of operating & design conditions is important. In general, for all IPDS pressure and temperature of the process are given.
Design conditions are something that the instrument may experience at very low intervals or may not experience at all. The low interval could be the startup of a plant, or shut down of the plant.
Note: It’s not advisable to collect the process data and blindly follow in instrument datasheet.
Sometimes you may notice different process data for different instruments on the same line.
In case of strange data, you may consult your process depart and get clarity before you proceed.
There could be a problem with unit conversion, and decimal separation.
Care must be taken when you import process raw data into automated instrument datasheet tools.
Step 4: Get the mechanical/material/piping data
We normally follow piping material specification documents for specifying material required for instrumentation items. The logic for the same is simple, fluid will pass through all piping components and so it is applicable for instruments mounted on/connected to the pipe. Generally, the material of construction and end connection rating shall be as per piping material specification.
The above section is more important for Control valves, on-off valves, and inline flowmeters. For other instruments sometimes project requirement calls for minimum SS316 material wetted part unless otherwise specified or better as required by PMS.
The pressure gauge sensing element shall be of SS316 as a minimum or better as required by PMS.
e.g. if the piping material is HASTELLOY C276 [one of the few alloys resistant to wet chloride gas, hypochlorite, and chlorine dioxide solutions] then the minimum case of SS316 would not be a good choice. Remember instrument material selection is also fit for purpose and suitable for specified service.
Step 5: Get the specific requirement for the instrument. Here it is important to know your project-specific requirement.
It is very important that we should understand the part list of instruments and specify the requirement for the instrument. Vendor catalogs, videos, literature, whitepaper, Installation, and operating manual are important sources to gather important & trending information.
Typical pressure gauge ranges are defined in section 3.2 of B40.1, Pressure Indicating Dial Type – Elastic Element Gauges
In Table 1 of B40.1, Accuracy grades are defined as 4A, 3A, 2A, 1A, A, B, C, and D.
Grade 4A = 0.1% FS error is permissible
Grade 1A = 1% FS error is permissible
Grade D = 5% FS error is permissible
The following is a typical dial size and accuracy class defined in EN 837-1.
Generally, the cost of Pressure Gauges varies based on specification. However, to get a rough idea it is around 2500 INR to 8000 INR. The more stringent the requirement is so is the cost.
Once the pressure gauge from the approved vendor list is finalized and is fit for purpose, then the pressure gauge datasheet is revised to cover vendor supplied/offered details, make and model, and purchase requisition number.
If you have process data where max operating pressure is 5 Kg/cm2g and design pressure is 17 Kg/cm2g. What calibration range and accessories would you consider for the pressure gauge? Remember pressure gauge standard range as per EN 837-1 / ASME B40.1
Disclaimer: The information shared is intended only for informational & educational purposes. All content mentioned does not constitute professional advice and is not guaranteed to be accurate, complete, reliable, up-to-date, or error-free.
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