Calibration Gas - Tec Trek Web Site

Tip of the Week

A Hydrocarbon by any other name, is not the same!

While reviewing the quarterly ASH calibration/inspection sheets, an inspector contacted me and posed the question, " Is it standard/common procedure to calibrate ASH Detectors with Pentane gas?"

I then asked, is this for a fixed or portable gas detector? which then prompted the following questions that I will answer in order.

What is the difference between fixed and portable detectors when it comes to calibration gas used?

Hand portable detectors are not site specific they can be used in a variety of locations and environment for the detection of different hydrocarbons. Fixed detectors are selected and located for a specific hydrocarbon base on the vapor density of the target gas.

What gas should be used?

When calibrating fixed hydrocarbon detectors, it is important that you know the target gas to be monitored. In this case, on an offshore production facility, our target gas is Natural Gas, which is comprised primarily of Methane. According to the manufacture of the detector, if your target gas is Natural Gas, you will use Methane and will calibrate the device with 50 % of full scale detector reading in this case 100% LEL. This means that you will use 2.5% Methane for calibration. Keep in mind that 5% Methane is 100% LEL.

What is the difference between Pentane & Methane Gas?

Both are hydrocarbons, but have different characteristics. However since our target gas is Natural Gas, which is 75-90% Methane, our detectors should be calibrated with Methane in accordance with the Manufactures recommendations. Pentane constitutes less that 5% of Natural Gas. Natural Gas, through processing, can be subdivided into 10 Hydrocarbons, which all have different characteristics.

Will the ASH detector work if calibrated with Pentane?

Yes, the detector will detect any hydrocarbon, but the readings will vary depending on the concentration. They will not be the same had the unit been calibrated for Methane.

Why are portable units calibrated with Pentane?

Because of the fact that they are portable, it is not certain of the location, environment and characteristics of the target gas. Offshore production facilities differ from other locations like hydrocarbon tank farms and processing plants. For the later two facilities, we must also consider the heavy hydrocarbons.

Would this be considered an INC ?

This is a matter of opinion and I am not authorized to determine if and INC should be written. However,
based on the PINC's list, CFR and API Standards

P-154
Gas Detectors to be installed in strict accordance with Manufactures recommend practice, API RP 14 C,G,&F and ANSI/ISA Standards.

G-856
Is the individual conducting the calibration/inspection of the Production Safety System properly trained to perform his/her duties per 30CFR250.1500.

If you require more information regarding the terms and explanations above, contact me by email or phone for assistance.

The above information is covered in the following Tec Trek class segments: Awareness Training (FG-01A), Basic Technical Training (FG-01)

For more information regarding training schedules and course curriculum, please visit our Web Site at www.tectrek.org

or Contact Todd Olivier at (337) 298-7959.

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Email: todd@tectrek.org