LNG Sampling Systems
Welker's LNG sampling systems are purpose-built around one fundamental imperative: the total and complete vaporization of the LNG sample — engineered, built, and tested at Welker to ISO 8943: 2025 and API 8.6 standards.
Welker LNG VAPORIZER System & INTERMITTENT SYSTEM
The Most Critical Step in LNG Custody Transfer
LNG is natural gas cooled to approximately -265°F — around 600 times denser than in its gaseous state. Sampling it accurately requires one non-negotiable step: total and complete vaporization before the sample reaches any cylinder or analyzer. Partial vaporization means heavier components separate out, the sample becomes unrepresentative, and custody transfer billing is wrong.
From Cryogenic Pipeline to Sample in Six Steps
Cryogenic Probe Extraction
Welker's patented cryogenic probe draws sub-cooled LNG from the flowing pipeline. The probe tip check valve begins vaporization at the point of entry — preventing compositional separation and line pack before the sample reaches the cabinet.
Heat-Traced Insulated Line
Customer-supplied heat-traced, insulated tubing maintains the sample in its sub-cooled state from the probe tip to the cabinet inlet — preserving sample integrity across the critical transfer distance to the vaporizer.
Complete Vaporization
The 2,000W heated vaporizer converts the LNG to gas completely and controllably. An impingement block ensures any remaining liquid droplets are fully vaporized before the gas stream continues — no partial vaporization, no fractionation.
Accumulator Conditioning
The fully vaporized gas is conditioned in a heated accumulator, which buffers the sample, ensures homogeneity, and provides regulated, stable gas flow to the downstream cylinders or online GC.
Cylinder Collection or Online GC
Conditioned gas is delivered to CP-2 Constant Pressure Cylinders or SC Single Cavity Cylinders for lab transport, or directed continuously to an on-site online gas chromatograph for real-time custody transfer measurement .
Analysis → Custody Transfer Billing
GC analysis determines BTU content and full LNG composition. Combined with density and quantity transferred, this produces the commercial value of the cargo for GIIGNL-compliant custody transfer billing and documentation.
Find Your LNG Sampling System
Answer two questions about your sampling method and sample destination and we'll point you to the right ISO 8943 configuration.
1. What sampling method does your application require?
2. Where does your vaporized sample need to go?
Three ISO 8943 LNG Sampling Systems
Every Welker LNG system includes the patented cryogenic probe, heated vaporizer, and accumulator. The configuration differs in how the vaporized sample is collected and delivered.
Vaporizing System
Continuous sampling → Online GC
The core Welker LNG system. A continuous stream of LNG is drawn through the patented cryogenic probe, completely vaporized in the heated chamber, conditioned in the accumulator, and delivered in real time to an online gas chromatograph.
Key Features
- Patented probe tip check valve — vaporization begins at probe entry
- 2,000W heated vaporizer — complete, controlled phase change
- Heated accumulator — homogeneous, stable gas delivery
- Continuous gas output to online GC for real-time analysis
- 316/316L stainless steel
Key Specifications
Best Application Fit
Vaporizing + Spot Sampling System
Continuous GC analysis + simultaneous cylinder collection
A configuration delivering vaporized LNG to SC Single Cavity Cylinders for laboratory verification. The accumulator splits conditioned gas to both outputs — providing the gold standard for high-value custody transfer where independent dual verification is required.
Key Features
- Dual output: simultaneous GC + cylinder collection from one vaporizer
- Online measurement and laboratory backup in a single system
- Ideal where dual verification is contractually required
- Same patented probe, vaporizer, and accumulator as System 1
- SC Single Cavity Cylinders collected as reference samples for dispute resolution
- Compatible with GIIGNL custody transfer documentation
Key Specifications
Best Application Fit
Vaporizing + Intermittent Sampling System
Timed spot grabs →CP-2 cylinders → Laboratory GC
The intermittent system collects discrete spot grabs of vaporized LNG into Welker CP-2 Constant Pressure Cylinders at timed intervals throughout the transfer. Sealed cylinders are transported to a laboratory for GC analysis. Welker's CP-2 design is the origin of ISO 8943 Figure 3 — Welker invented the method that became the global standard.
Key Features
- Welker CP cylinder — the origin of ISO 8943 Figure 3
- Floating piston maintains sample pressure during transport to lab
- No on-site GC required — lab-based analysis from sealed cylinder
- Multiple cylinders collected sequentially for composite representation
- Pre-cooled cylinder chilling cycle ensures cryogenic sample integrity
Key Specifications
Best Application Fit
System Comparison
Use this table to match system configuration against your GC availability, sampling requirements, and custody transfer documentation needs.
| Specification | System 1 — Vaporizing | System 2 — Vaporizing + Spot | System 3 — Vaporizing + Intermittent |
|---|---|---|---|
| Sampling Method | Continuous | Continuous + Spot | Intermittent Spot Grabs |
| Online GC Output | ✔ Direct Connection | ✔ Direct Connection | ✗ Lab GC only |
| Cylinder Collection | ✗ | ✔ Single Cavity Cylinders | ✔ Constant Pressure Cylinders |
| Real-Time Custody Data | ✔ | ✔ | ✗ Lab results after transfer |
| Patented Cryogenic Probe | ✔ | ✔ | ✔ |
| Heated Vaporizer (2,000W) | ✔ | ✔ | ✔ |
| Heated Accumulator | ✔ | ✔ | ✔ |
| On-Site GC Required | ✔ For GC output | ✔ For GC output | ✗ |
| MAOP | 275 psig | 275 psig | 275 psig |
| Construction | 316/316L SS | 316/316L SS | 316/316L SS |
Ready to Configure Your LNG Sampling System?
Our LNG sampling engineers will help you select the right configuration for your terminal, GC availability, custody transfer requirements, and sampling standards.