Use of Portable X-Ray Fluorescence for Detecting and Quantifying Mercury Contamination Out in the Field

insights from industryMichael HullProduct Manager Evident Corporation

In this interview, Michael Hull talks about using portable X-ray fluorescence for detecting and quantifying mercury contamination in the field.

What are the health and environmental risks associated with different forms of mercury in crude oil?

In the petroleum stream or crude oil, mercury usually takes one of two forms. Sweet crude is typically present in the form of mercury zero. When we say mercury zero, we should put this in parentheses because several organomercury compounds could be present in sweet crude, not just the quicksilver mercury.

Mercury is usually found in sour crude as mercury sulfide or cinnabar compounds. However, there is little difference in the type of mercury being discussed. Both of these mercury compounds are extremely harmful. Even with the sour crude, the mercury sulfide is converted to organomercury compounds during the roasting and cracking, which are highly toxic to human life and the environment.

These organomercury compounds have a relatively high vapor pressure, increasing the risk of inhalation.

What challenges does the oil and gas industry face with regard to mercury contamination in the field?

One of the challenges with mercury, particularly in the oil and gas industry, is how it is intercalated into the physical assets. Mercury, like sticky peanut butter, tends to stick to the surface of structures and is hard to remove.

Even if the mercury concentration is relatively low, even as low as two PPM, constant exposure leads to the mercury becoming intercalated into the surface of the structural component. It is almost like a filtering process, where the mercury comes from the crude oil but gets intercalated or stuck into the steel pipeline or whatever material is used.

The challenge, of course, is that these binding patterns are extremely complicated. There are multiple mercury compounds, so there is no simple cleanup method. A simple detergent or chelate cannot remove all mercury because of the complex mercury species and their binding patterns.

What are the existing methods for detecting mercury? What are the key criteria for an efficient method to detect and quantify mercury contamination in the field?

The most common existing devices for detecting mercury are sniffer-like tools. However, when mercury is detected with a sniffer, it is already in the air and volatilized, which means you are monitoring exposure rather than limiting it.

In an ideal world, mercury exposure should be prevented. To do this, direct contact with contaminated surfaces must be avoided. The mercury cannot be seen with the naked eye. Therefore, a detection method is needed to determine which surfaces are contaminated and which are not, and this should be done before anything that might volatilize these mercury compounds, such as welding, cutting, or any torch effect.

Let us discuss some analytical considerations to detect and quantify mercury contamination in the field. If we compile a wish list under ideal conditions, we would want a fast technique. We do not want something labor-intensive that takes time to collect the sample and send it to the lab, causing delays in production and work. The technique must also be accurate to ensure the data is reliable when performing risk analysis. Ideally, it should also be non-disturbing so that it can be done preemptively, focusing on exposure prevention rather than exposure monitoring.

How can portable XRF devices be used in field settings for testing surface mercury contamination?

Handheld or portable X-ray fluorescence (XRF) can provide fast, accurate, and in situ measurements of surface mercury. These handheld instruments can be carried out into the field and operated with battery power that lasts all day. They feature a very clear user interface providing mercury surface concentration without disturbing the sample.

XRF is an X-ray technique that is quite safe when operated properly. It works by emitting X-rays from the instrument, which penetrate the sample (such as a pipe, handrail, or platform catwalk), and are then emitted back from the sample. The sample absorbs these X-rays, and the elements in the sample become energized and emit X-rays of their own. However, the emitted X-rays differ from those initially sent out by the instrument.

The X-rays emitted by iron differ from those emitted by chromium, nickel, and, in this case, mercury, which is the element of interest. The instrument works like a smartphone's spectrometer or digital camera; it captures these emitted X-rays, converts them into a signal, and processes them using an internal mini-computer.

Ultimately, the solution provided is the material chemistry, specifically, the amount of mercury contamination on the surface. This entire process is nondestructive and operates at the speed of light, typically taking less than 10 seconds to perform a test, with an average of three to five seconds. This makes it very fast, accurate, and suitable for use directly in the field, such as on production rigs, along pipelines, or anywhere else in the refinery where testing is needed.

Can portable XRF be used to assess mercury contamination across different materials or structures?

It is important to be able to measure any type of surface, as various assets could potentially be contaminated. These include different alloys such as carbon steel, stainless steel, naval brass, and even galvanized materials. Additionally, there are other items like plastic tanks, barrels, equipment, handrails, platforms, and catwalks that could harbor mercury contamination due to oil exposure.

Given the diverse range of structures or components that may require inspection, it is important to have an XRF instrument that can measure independently of the substrate. Inspectors or operators should be able to conduct these inspections without a degree in analytical chemistry or prior knowledge of the substrate. To address this, we have worked with our clients in Houston to ensure that our calibration is substrate-independent.

How reliable is the accuracy and precision of handheld XRF devices for detecting mercury contamination?

In terms of accuracy, we can observe consistent results across a wide concentration range, exceeding 30 micrograms per square centimeter of mercury, using certified reference samples. These samples ensure no false positive, as shown by zero reports on the blanks. There is an excellent linearity demonstrated across a large concentration range within the reference material.

Regarding action levels, while there is no fixed industrial standard, many of our clients use 10 micrograms per square centimeter. Our measurements have shown concentrations surpassing 30 micrograms per square centimeter and even exceeding 100 micrograms per square centimeter. However, once mercury levels reach such high concentrations, whether it is 99 or 101 micrograms per square centimeter, it signifies a problem that needs attention.

Looking at repeatability or instrument precision, conducting six repeat tests on the same sample with our reference standard yielded consistent results: 12, 13, 12, 12, 12, and 12 micrograms per square centimeter. This indicates good precision and repeatability, with a margin of error of less than 0.6 micrograms per square centimeter and a relative standard deviation of 5%.

About Michael Hull

Michael is a Materials scientist experienced in applying a fundamental understanding of chemistry to solve challenges in a variety of industries, ranging from mining to manufacturing. He has  a Ph.D. in inorganic chemistry, with over a decade of experience conducting interdisciplinary research and materials characterization, including organic, organometallic, & inorganic compounds. 

This information has been sourced, reviewed and adapted from materials provided by Evident.

For more information on this source, please visit Evident.