Sampling Cylinders: Stainless Steel & High-Alloy Sample Cylinders for Gas & Liquid Sampling
A sampling cylinder is a portable, code-rated pressure vessel. It captures a representative gas or liquid sample pulled from a live process line, then transports and stores it for off-line laboratory analysis. Crestflo supplies these cylinders across the full instrumentation alloy range, from 316 and 316L stainless through 6Mo, duplex and the nickel alloys. They're built in single-ended, double-ended, fixed-volume and constant-pressure configurations, made to the applicable DOT/TC pressure-vessel specification, with heat-number traceability and delivery running 6 to 8 weeks.
On this page, "sample cylinder" refers to a pressure vessel used in fluid-system sampling for process gas and liquid analysis. It's not a compressed-gas storage bottle, not an SCBA or breathing cylinder, and not an engine (piston or bore) cylinder. Reviewed by the Crestflo Engineering Team.
What a Sample Cylinder Is (Grab-Sample Vessel & Sample Bomb)
A sample cylinder is what holds a grab sample: a discrete slug of process fluid, trapped at line pressure, that captures the stream exactly as it was at the moment of sampling. Isolation valves at one or both ends close to seal the fluid inside, and the sealed cylinder then travels to the lab, where the sample is released for analysis without losing light ends or picking up contamination along the way. The captured fluid has to stay representative the whole trip from tap to bench, so the cylinder body, its valves, and its wetted seals all get chosen to match the media being sampled and its pressure. Single-ended cylinders fill and empty through one port. Double-ended cylinders carry a valve at each end, which means the vessel can be flushed through before the grab gets trapped, and that flushing step is what produces a cleaner, more representative sample.
Also Known As: Sample Cylinder, Sample Bomb & Grab-Sample Cylinder
Engineers call this vessel by different names, depending on the plant and the service it's used in. A sampling cylinder goes by sample cylinder or sample cylinder assembly too; in oilfield and gas-plant circles, it's often a sample bomb, sampling bomb, or gas sample bomb. Put it in a spot-sampling panel and it becomes a grab sample cylinder. Name it by the media it holds, and you get a gas sample cylinder or gas sampling cylinder, a natural gas sample cylinder, a liquid sampling cylinder, a crude oil sample cylinder, or an LPG / NGL sample cylinder. Configuration gives it yet more names: single-ended (SE) or double-ended (DE) cylinder, fixed-volume cylinder, or constant-pressure, floating-piston, or piston sample cylinder. Transport specifications add still more. It's a DOT sample cylinder (DOT-3E, DOT-3A, or DOT-3AA) in the US, or a TC-3EM / TC-3AAM cylinder in Canada.
Sample Cylinder Types: Single-Ended, Double-Ended, Fixed-Volume & Constant-Pressure
Configuration depends on how the sample gets filled, whether the vessel is flushed through, and whether the fluid is allowed to flash. The values below reflect standard sampling practice, but they can be adjusted as needed.
| Configuration | Ends | How it works | Best for |
|---|---|---|---|
| Single-ended (SE), fixed-volume | One valve | Fill and empty through the same port into a fixed internal volume | Stable gases and liquids; simple grab sampling |
| Double-ended (DE), fixed-volume | Valve at each end | Flow-through purge of the cylinder before the grab is trapped | Cleaner, more representative samples; trace work |
| Constant-pressure (CP) / floating-piston | One or two valves + piston | A piston isolates the sample from an inert pre-charge, holding it at line pressure | Volatile liquids, NGL, LPG, crude, that must stay single-phase |
| Spring-loaded / mixer | Piston with internal spring or mixer | Maintains pressure and helps re-homogenize the sample before analysis | Multi-phase or waxy samples that stratify |
Fixed-volume cylinders handle gas and stable liquids just fine, and they're the standard choice for most jobs. But a volatile liquid is a different story. Drop the pressure even slightly and it flashes to two phases, so a constant-pressure or floating-piston cylinder gets specified instead. The pre-charge holds the trapped sample above its bubble point, which means it stays intact all the way to the lab and arrives representative of what was actually pulled.
High-Pressure Sample Cylinder Ratings & DOT / TC Specifications
Portable sample cylinders carry markings under either US DOT (49 CFR) or Transport Canada pressure-vessel specifications. These specs govern the design, the materials, the testing, and the retest schedule. The service pressures listed below are the standard published values for each specification. Which specification a given build is marked to, and its rated service pressure, gets confirmed in the quote, and both can be adjusted to what the job requires.
| DOT / TC specification | Typical marked service pressure | Requalification (retest) | Notes |
|---|---|---|---|
| DOT-3E / TC-3EM | ~1,800 psig | Exempt from periodic retest (per 49 CFR §178.42) | Small seamless cylinders; common for routine gas grabs |
| DOT-3A / TC-3AM | 1,800 / 1,875 psig and up (per marked class) | 5 or 10-year hydrostatic, per stamp | Seamless steel; 1,875 psig is a common marked band; higher service pressures on request |
| DOT-3AA / TC-3AAM | To 3,000 / 5,000 psig service | 5 or 10-year hydrostatic, per stamp | High-tensile seamless; high-pressure service |
| DOT special permit (SP) | Per permit | Per permit | Non-standard designs / materials |
Design and testing follow 49 CFR §178.36–37 (3A/3AA) and §178.42 (3E), with Transport Canada equivalents in place too. Hydrostatic proof, and lot burst testing where it's required, prove each build. Match the specification to your sample's maximum pressure and the transport rules that apply to it.
Sample Cylinder Materials: 316L, 904L, 6Mo, Duplex, Inconel, Monel & Hastelloy
Choosing the body and wetted-seal material comes down to how corrosive the sampled stream is. For general process sampling, 316/316L stainless is the go-to choice. As chlorides, acid concentration or H₂S climb, though, you'll need to move toward super-austenitic, duplex and nickel alloys. The UNS designations listed below are the standard published grade identifiers.
| Grade (UNS) | Family | Choose when |
|---|---|---|
| 304 / 304L (S30400 / S30403) | Austenitic stainless | Non-corrosive utility and general sampling |
| 316 / 316L (S31600 / S31603) | Austenitic stainless | General refinery, chemical and gas-plant sampling |
| 904L (N08904) | Super-austenitic stainless | Sulfuric / phosphoric acid and higher-chloride streams |
| Duplex 2205 (S32205) | Duplex stainless | Chloride stress-corrosion risk with higher strength |
| Super Duplex 2507 (S32750) | Super duplex | Seawater, brine and aggressive chloride service |
| 254 SMO (S31254) / AL-6XN (N08367) | 6Mo super-austenitic | High-chloride, oxidizing and pitting-prone media |
| Alloy 20 (N08020) | Nickel-iron-chromium | Hot sulfuric acid streams |
| Monel 400 (N04400) | Nickel-copper | Hydrofluoric acid and reducing service |
| Inconel 625 (N06625) / 825 (N08825) | Nickel-chromium | High-temperature and mixed-acid corrosion |
| Hastelloy C-276 (N10276) | Nickel-molybdenum-chromium | Wet chlorine, hypochlorite and severe acids |
| Titanium Gr2 (R50400) | Titanium | Oxidizing chlorides and seawater |
For sour (H₂S) service, Crestflo supplies wetted components that meet NACE MR0175 / ISO 15156 material requirements. Which grade to use depends on the media involved, and that's laid out in the material selection by service guide and the sour-service selection under NACE. Each alloy has its own dedicated page: 316/316L, 254 SMO, AL-6XN, Super Duplex 2507, Inconel 625, Monel 400, and Hastelloy C-276.
Sample Cylinder Components: Outage Tube, Rupture Disc & Valve Ends
Past the vessel itself and its isolation valves, a sample cylinder needs safety and handling components chosen to fit the service.
- Outage tube (dip tube): It leaves a permanent vapor space in the cylinder, usually around 20%, which caps the maximum liquid fill at about 80%. Without that gap, thermal expansion of trapped liquid could hydraulically overpressure the cylinder as temperatures climb.
- Rupture disc (rupture disk): A burst-pressure relief element. Its purpose is simple: guard the cylinder against accidental overpressure or overfill.
- Needle-valve or ball-valve ends: Integral isolation valves at one or both ends of the cylinder. When a job calls for fine, tight throttling on gas grabs, specify needle-valve ends.
- End caps, valve protectors and carrying handles: These shield the valves and thread ends during transit. They're also what makes a filled cylinder safe to carry.
End connections are supplied as NPT (per ASME B1.20.1) or as tube-fitting (compression) ends that are performance-qualified to ASTM F1387 and dimensionally interchange with the major instrumentation brands, in imperial and metric.
Cleaning, Finishes & Trace-Analysis Preparation
Surface preparation determines how clean the sample stays, and that matters most for trace analysis and reactive gases. Options follow the applicable published standard and can be customized to requirement:
- Electropolish and passivation give the internal surface a smooth, corrosion-resistant finish that cuts down on adsorption and holdup.
- Inert / trace-analysis coatings to reduce reaction and carry-over of low-concentration or reactive components.
- Oxygen cleaning to ASTM G93 / CGA G-4.1, the standards Crestflo follows for O₂ service and for clean sampling, since hydrocarbon residue would throw off the result.
Specify the target cleanliness or finish level on the RFQ and it is prepared to that specification.
Sample Cylinder Sizes, Volumes & How to Order
Sample-cylinder volumes come in a published series that runs from 10 cc up to 3,785 cc, or 1 US gallon, with the usual metric sizes listed alongside. The figures below are the standard published sizes. Nothing's locked in, though - they're customizable to whatever you need. From there, volume, pressure or DOT class, material, end configuration and options all get combined per order.
| Volume (cc) | Metric | Typical use |
|---|---|---|
| 10 cc | 10 mL | Micro grabs and trace work |
| 25 cc | 25 mL | Small gas grabs |
| 50 cc | 50 mL | Routine gas sampling |
| 75 cc | 75 mL | Routine gas and light-liquid sampling |
| 150 cc | 150 mL | General gas and liquid grabs |
| 300 cc | 300 mL | Larger gas and liquid samples |
| 500 cc | 500 mL | Liquid, NGL and LPG sampling |
| 1000 cc | 1 L | Liquid and constant-pressure work |
| 3,785 cc | 3.785 L (1 US gallon) | Bulk liquid and gallon grabs |
The ordering-code series is configured to each build, so specify volume, DOT/TC specification, wetted material, end configuration (SE / DE / constant-pressure), valve ends, and any outage tube, rupture disc, or cleaning option. Do this whether you're trapping a cylinder for gas sampling or pulling a liquid grab, so the sample that reaches the lab is truly representative. A datasheet or sample drawing can be sent along too. Datasheets and CAD models are available to customers on request, and Crestflo's engineering team can provide the ordering-code guide for a standard configuration. Pricing isn't listed live. Request a quote or request a sample, and you'll get back a configured, priced offer.
Where Sample Cylinders Are Used: Gas, NGL, Crude & Analytical Sampling
Any plant that needs a representative off-line sample of a pressurized fluid relies on sample cylinders. That covers natural gas, NGL and LPG sampling for composition and BTU checks, crude and refined-product sampling, and sour-gas grabs in oil and gas midstream and petrochemical and chemical service. In the lab and at the panel, these cylinders feed analytical sampling systems and emissions work. On the process side, the cylinder acts as the capture vessel inside an engineered grab sampling system, paired with isolation valves, filters and, for gas, a pressure-reducing regulator.
Standards, Certifications & Traceability
Crestflo holds ISO 9001 / 14001 / 45001 and PED certification. Every cylinder carries a heat/lot number and ships standard with an EN 10204 3.1 material test certificate; a 3.2 is available on request. Cylinders are built to the applicable DOT / TC pressure-vessel specification. Tube-fitting end connections are performance-qualified to ASTM F1387, NPT threads conform to ASME B1.20.1, and sour-service builds meet NACE MR0175 / ISO 15156. Testing covers hydrostatic proof, PMI, and in-house non-destructive testing; destructive testing happens at ISO/IEC 17025-accredited laboratories, with third-party inspection available on request. For more, see material test certificates & traceability and oxygen / UHP cleaning.
Why Buy Sample Cylinders from Crestflo
Crestflo supplies sampling cylinders to the US market, and it's the instrumentation division of an export house that's been operating for four decades, recognized by the Government of India, with a long track record delivering into the Middle East. Most suppliers stop at a 316 stainless catalog line. Crestflo doesn't. It builds sample cylinders across the full alloy range, for the streams that actually demand it:
- Built for sour and CRA service: The line spans 316L through 6Mo, duplex, Alloy 20, Monel, Inconel and Hastelloy, with every grade suited to sour, chloride and acid sampling. This isn't a stainless-only lineup.
- Interchange that's actually proven: Tube-fitting end connections are performance-qualified to ASTM F1387 and match the majors dimensionally, so cylinders drop straight into existing loops.
- Delivery you can plan around: Standard items ship from stock, specials are made to order, and lead times run 6–8 weeks. Compare that to the 20-plus weeks typical of the majors.
- Traceability comes standard, not as an add-on. Every cylinder carries heat-number marking and an EN 10204 3.1 MTC (3.2 available on request), backed by PMI and NDT.
- Small MOQ and private label for distributors and OEMs, cost-competitive after US duties.
- Honest origin: Made in India, with full material traceability behind every batch. Need domestic-melt or TAA-eligible material? US and European melt can be supplied on request.
Talk to the Crestflo Engineering Team: sales@crestflousa.com · +1 346 594 9005 (Houston, TX). Request a quote · request a sample · become a distributor.
Sample Cylinder FAQ
What is a sample cylinder?
A sample cylinder is a code-rated pressure vessel built to pull a representative gas or liquid sample from a process line at line pressure, then hold it safely until it reaches a lab for analysis. Some call it a sampling cylinder. In oilfield and gas-plant settings, it's often known by a blunter name: a sample bomb.
What is the difference between single-ended and double-ended sample cylinders?
A single-ended cylinder has one valve, so it fills and empties through the same port; a double-ended cylinder has a valve at each end, letting the vessel be flushed through with fresh fluid before the grab is trapped. Double-ended cylinders give a cleaner, more representative sample and are preferred for trace and analytical work.
What is a constant-pressure (floating-piston) sample cylinder for?
A constant-pressure cylinder relies on an internal piston to keep the sample separate from an inert pre-charge gas, holding it at line pressure the whole time. This keeps volatile liquids like NGL, LPG and crude single-phase from tap to lab. They won't flash to two phases when pressure drops, and the sample stays representative.
What is the outage tube for?
The outage tube leaves a permanent vapor space in the cylinder, typically around 20%, which caps the maximum liquid fill at 80%. This prevents thermal expansion of trapped liquid from hydraulically over-pressuring the vessel as its temperature climbs. It's a core overfill-safety feature on liquid sampling cylinders.
Which materials are available for sample cylinders?
Standard construction uses 304/304L and 316/316L stainless. When the service turns corrosive or sour, we move up to 904L, 254 SMO, AL-6XN (6Mo), Duplex 2205, Super Duplex 2507, Alloy 20, Monel 400, Inconel 625/825, Hastelloy C-276, and Titanium Gr2. Grade selection matches the corrosivity of the sampled stream.
Are sample cylinders available for sour (H₂S) service?
Yes. Wetted components meet NACE MR0175 / ISO 15156 material requirements for sour service. The corrosion-resistant alloy is selected based on the stream's H₂S, chloride and temperature conditions. Please confirm the sour-service alloy on the RFQ.
What pressure ratings and DOT / TC specifications are available?
Sample cylinders get built and marked to US DOT and Transport Canada pressure-vessel specs, DOT-3E/TC-3EM at roughly 1,800 psig, plus DOT-3A/3AA and TC-3AM/3AAM for higher service pressures running 3,000 to 5,000 psig. The marked spec and rated service pressure for your particular build get confirmed in the quote.
Do you provide material certificates and traceability?
Yes. Every cylinder carries a heat/lot number. It ships standard with an EN 10204 3.1 material test certificate, and we'll issue a 3.2 on request. Both are backed by PMI and in-house non-destructive testing. Crestflo holds ISO 9001, 14001, and 45001 certification, plus PED.
Can sample cylinders be oxygen-cleaned or prepared for trace analysis?
Yes. Electropolishing, passivation, inert trace-analysis coatings, and oxygen cleaning to ASTM G93 and CGA G-4.1 are available on request. Just note the cleanliness or finish level you're after on the RFQ.
Can Crestflo match Swagelok, Hoke or Fitok cylinder end connections?
Tube-fitting and NPT end connections match dimensionally and are performance-qualified to ASTM F1387. Swagelok®, Hoke® and Fitok® are trademarks of their respective owners; we cite them strictly for identification and interchange reference, and no affiliation or endorsement is implied. Need a specific part-number match? Reach out to the Crestflo engineering team through the cross-reference program.
What is the lead time, and where are the cylinders made?
Typical delivery runs 6–8 weeks, well ahead of the 20-plus weeks common from the majors. Standard items ship from ready stock, while specials are made to order, and we offer small MOQs along with private-label options. Standard product is of Indian origin with full material traceability. US and European melt can be arranged on request for jobs that call for domestic-melt or TAA-eligible material.
Related Products & Resources
- All instrumentation accessories
- Crestflo runs a deep accessory lineup. Grab sampling systems, Needle valves, Inline filters, Gauge savers and Snubbers all fall under one roof, ready for demanding instrumentation runs.
- Industry reach is broad too. Analytical sampling systems sit alongside Oil & gas midstream work, and Petrochemical & chemical plants round out the list.
- Materials and paperwork matter just as much. There's 316/316L material, certification against NACE MR0175 and ASTM F1387, traceable EN 10204 MTC documentation, and Oxygen / UHP cleaning for the toughest applications.
- Reviewed by the Crestflo Engineering Team