A complete request for quotation (RFQ) gets you offers you can compare and fewer rounds of clarification. For cryogenic and LNG valves, the design temperatures, the test requirements and the list of documents all change what a supplier offers and what it costs, so state them in the first request.
The checklist below is per valve tag. A completed valve datasheet for each tag is the best attachment; the list shows what the datasheet must cover.
The checklist
| Item | What to state | Why it matters |
|---|---|---|
| Service fluid | LNG, liquid nitrogen, liquid oxygen, liquid hydrogen or other; liquid, vapour or two-phase | Decides materials and seals, and any special cleaning, such as cleaning for oxygen service |
| Design temperatures | Minimum and maximum design temperature, and the normal operating temperature | Decides materials, the bonnet extension and the test temperature |
| Pressure | Pressure class or PN, design pressure, and the largest pressure difference the closed valve must hold | Decides the body rating and the seat design |
| Size | DN or NPS; pipe schedule or wall thickness for weld ends | Weld ends have to match the pipe |
| Valve type and duty | Ball, gate, globe, butterfly or check; isolation, control or regulation; flow direction if the valve seals one way only | Decides the design and which standards apply |
| End connections | Butt weld, socket weld or flanged, with the flange facing | Has to match the line and the pipe material |
| Materials | Body, bonnet, trim, seat and seal materials, or the material specification your project uses | Not every material keeps its toughness in the cold |
| Bonnet extension and orientation | The extension required, and how the valve will be installed (stem upright or at an angle) | The extension keeps the stem seal away from the cold; suppliers set orientation limits |
| Testing and leakage | The standard and its edition, the tests required (shell, seat, low-temperature), the acceptable seat leakage, and whether tests are witnessed | "Cryogenic tested" on its own does not say how, at what temperature or to what leakage limit |
| Actuation | Manual, gear, pneumatic, electric or hydraulic; fail position; air or power supply; positioner, switches or solenoid valves | Often priced as a separate part of the offer; stating it avoids gaps |
| Documents | Material certificates, test reports, drawings, manuals and any certificates your project requires, with format and schedule | Documents that are not listed may not be in the offer |
| Quantity and spares | Number of valves per tag, and spares for commissioning and operation | Spares are easiest to price together with the valves |
| Delivery | Delivery point, Incoterms, required date, packing and preservation (end caps, cleanliness) | Decides freight, the transfer of risk and packing |
| Inspection | Hold and witness points, third-party inspection, and who attends tests | Witnessed tests have to be planned into the schedule |
Cavity relief on ball and gate valves
In a closed ball or gate valve, liquid can be trapped in the body cavity. As it warms it turns to gas, and the pressure in the cavity can rise well above line pressure. Cryogenic designs give the cavity a relief path, often towards the upstream side, which means the valve seals in one direction only.
If your piping needs a particular arrangement, say so in the RFQ, and mark the flow direction on the datasheet and the drawings.
Attach these
- A valve datasheet for each tag
- The relevant extract of the line list or P&ID
- Your project's valve and piping specification sections
- The vendor document requirements list
- Tagging and marking requirements
Gaps that slow down an offer
Not sure which test standard to name? See cryogenic valve testing standards.
- An operating temperature with no minimum design temperature
- A pressure class with no pressure difference the closed valve must hold
- "Cryogenic tested" with no standard, test temperature or leakage limit
- No list of documents
- No delivery point or Incoterms
Questions
- Should I send a datasheet or a description?
- A datasheet for each valve tag. It covers the details in a fixed layout, so offers from different suppliers are easier to compare.
- Do I need to name a test standard in the RFQ?
- Yes. "Cryogenic tested" on its own does not say how, at what temperature or to what leakage limit. Name the standard, its edition and any project additions.
- Why state the flow direction for a cryogenic ball valve?
- A ball valve with a cavity relief path seals in one direction only. The flow direction on the datasheet has to match the way the valve will be installed.
Published by EVOSNT Trading FZCO (EVO LNG Supply). General guidance for engineers and buyers; the purchaser's specification and the applicable standards govern the design and testing of any valve. See our valve range.
