Refineries in Northern California take numerous samples to verify the composition and consistency of hydrocarbons such as methane, propane, acetylene, ethane, kerosene, naphtha, diesel distillate, and asphalt as they are produced during the various stages of the refining process. The majority of samples are taken under pressure using sample bombs or cylinders to capture and preserve representative samples of the liquids and gases.
We’ve already extensively covered grab sampling system design, safety, quality control, and process analyzers. Here, we want to focus on the use of sample bombs for oil and gas that are critical in transporting pressurized gas and liquid from the sample station to the analyzer station or laboratory and the various sample bomb options available for oil and gas analyses.
Although you might be tempted to order sample bombs in quantity, almost as if they are a commodity when you’re using dozens to hundreds a day for sampling, you stand to improve sampling process efficiency and the sample quality with the right sample bomb options.
In essence, sample bombs should efficiently capture oil or gas under pressure and preserve these samples as they are transported from the sampling station to the laboratory. And, of course, safety throughout the capture and transportation processes is a requirement for stable and secure storage of collected samples.
Sample bombs are fabricated from seamless tubing for consistent wall thickness, size, and capacity. The tubing is typically 304L or 316L stainless, but you also have the option of using 400 alloy (nickel-copper alloy with exceptional resistance to corrosion), or alloy C-276 (excellent resistance to both oxidizing and non-oxidizing acids) to better accommodate sample fluids and minimize corrosion issues that could contaminate the sample. SilcoNert® 2000, an inert, nonreactive silicon coating, can be used to line sample bombs to provide better process control, consistent sampling, and analytical results.
Sample bombs need to be matched to the required sample volume and the potential for the liquid or gas sample to expand/increase pressure in the event of higher than normal/ambient temperatures during transportation. Standard cylinder sizes are 150, 300, 400, 500 and 1,000 cm3.
Outage tubes within the sample bomb provide a vapor space of the desired volume. They are a safety mechanism, allowing a pressurized liquid to expand if the temperature increases—particularly important with volatile compounds, which readily evaporate at lower pressures. Without sufficient vapor space, a small temperature increase may cause the liquid to expand and dangerously increase the pressure, compromising operator safety.
The outage is the vapor space in the sample bomb expressed as a percentage of the total sample bomb volume. Here’s the formula:
% outage = (vapor space/total volume) × 100
The length of the outage tube determines the amount of vapor space in the sample bomb. Outage tubes are made from 316 stainless steel or alloy 400 tubing. Outage tubes lengths can be specified to provide 10%, 20%, 30%, 40%, or 50% vapor space. Depending on the vendor, you may be able to order by length or by percentage.
The interior of the sample bombs can affect sample quality. For most sampling conditions 304L, 316, and 316L stainless, 400 alloy, or C-276 alloy meet the need. However, for some gases and liquids that are exceptionally corrosive or have a tendency for adsorption or absorption, surface treatments or coatings help maintain a representative sample.
Sample bombs can be ordered with electropolishing (improves the corrosion resistance of 316 and 400), PTFE coating (heat resistant, almost total chemically inert, low coefficient of friction), or SilcoNert® to fight corrosion or reduce absorption and adsorption of sample fluids and gases into the sample bomb’s surface, and make it easier to purge sample bombs of residual fluids.
Most sample bomb purge systems don’t clear out the area between the quick connect and valve (only the panel, feed, and hose. However, sample bombs can be ordered with a purge bypass tube that allows an inert gas such as nitrogen to circulate through the connections on the sampling station to remove residual sampling fluid prior to or after taking a sample. The inert gas and any residual fluids are purged to vent. Purging helps ensure the capture of a representative, contamination-free sample.
Rupture disc units protect sample bombs from over pressurization by venting the contents into the atmosphere. A rupture disc is welded to a body that is threaded into a valve body or a rupture disc tee and sealed with an elastomer O-ring. A rupture disc is easily replaced without the need to remove the valve or the tee from the sample bomb. It’s recommended that you use a rupture disc with fluids that may rapidly expand and pressurize due to increased ambient temperatures. Rupture disc units are available for 1900 psig (130 bar) and 2800 psig (192 bar) pressure ratings. Some vendors may offer National Association of Corrosion Engineers (NACE) approved rupture discs to prevent corrosion, reducing the frequency of replacement.
Stainless steel quick-connects facilitate easy attachment and detachment of sample bombs from grab sampling stations. Quick-connects are rated for a wide range of pressures and temperatures, and offer unrestricted flow for fluid transfers, draining, and venting. Quick-connects are available in single- and double-end shutoff stem models and can be keyed to prevent accidental intermixing of different lines in multifluid or multi-pressure systems.
The optional carrying handle, constructed of 304 stainless steel, provides a convenient and safe way to carry sample bombs. Handles are available for 300 cm3 and larger sample bombs.
End caps protect valves from damage anytime the sample bomb is not attached to the grab sampling station. End caps act as a protective measure to deflect damage that may occur if a cylinder is dropped with the valve facing down and should comply with DOT regulations. End caps are made from plated carbon steel and are available for use on 2250 and 3785 cm3 sample bombs. End caps thread onto a neck ring attached to the cylinder neck. End caps can also protect angle-pattern valves used on sample bombs.
Sample bombs can be customized with roll stamped or laser-etched markings to meet specific identification requirements of Northern California refineries. Department, process, location, or serial numbers can easily be permanently marked on each sample bomb you order. As a precaution and best practice, Swagelok does not mark cylinders with the intended contents of the sample bomb.
Whether you’re looking to purchase sample bombs for a new analytic process, replace outdated sample bombs, or increase the number of sample bombs in your inventory to prevent “running out,” you’ll do well to work with a local vendor. Swagelok has facilities in Concord, Fremont, and Santa Clara and carries an extensive inventory of high-quality grab sampling systems and components. We have decades of experience in addressing the process needs of the oil and gas industry. Our field engineers are available to conduct onsite visits to your refinery to assess specific grab sampling processes and recommend sample bomb options that meet the specific analytic requirements of each process.
The expertise that our field engineers bring can save you significant time in determining the right sample bomb options for each of your sampling processes. As a result, you’ll obtain sample bombs that facilitate safe, efficient capture and transport of representative samples. And with Swagelok’s Northern California presence—we’re always accessible for follow-up technical guidance and support, as well as rapid delivery of parts or components to keep your grab sampling systems working properly.
To find out more about how Swagelok Northern California can assist you in troubleshooting and revolving gas pressure regulator problems by providing expert on-site consultation, contact our team today by calling 510-933-6200.