Selecting a Choke & Kill hose to API 16C — fire service levels, fire testing and shelf life
A practical guide for drilling engineers and procurement teams: what has to appear in the enquiry before a flexible choke and kill line can be quoted correctly.
What API 16C actually covers
API Specification 16C sets the requirements for design, materials, manufacture, testing, inspection, welding, marking, handling, storage and shipment of choke and kill equipment for the petroleum and natural gas industry — both surface and subsea. The flexible line is only one item in that scope; manifolds, valves and chokes fall under the same specification.
A pattern we see constantly in enquiries: the buyer writes only "API 16C hose". On its own that is not a purchasing specification. To build or supply the assembly, a manufacturer needs at minimum the working pressure, size, length, end connection, fire service level and whether the service is sour. Without them a quotation is either wrong or padded with margin for the unknowns.
Construction of a flexible choke and kill line
The conventional construction has three parts:
| Layer | Typical material | Function |
|---|---|---|
| Inner tube | Nitrile rubber (NBR) | Resistance to oil, abrasion, acid and alkali |
| Reinforcement | 2 to 8 layers of high-tensile spiral steel wire | Carries working pressure and pressure surge |
| Cover | Neoprene | Resistance to oil, abrasion, low temperature, weathering and ageing |
The number of reinforcement layers relates directly to the permissible working pressure. Common market ratings run from 5,000 to 15,000 psi, and the rating should follow the actual wellhead working pressure rather than defaulting to the highest grade available.
Fire Service Levels (FSL) — the clause most often left out
API 16C defines four fire service levels: FSL 0 through FSL 3. The higher the number, the more demanding the fire-resistance requirement, with FSL 3 intended for high-risk drilling operations.
In the fire test, the flexible line is exposed directly to flame or to radiation inside a furnace. At the end of the specified period — 5 to 30 minutes depending on the level — the temperature recorded by the thermocouples must be equal to or higher than 1,300 °F (704 °C), and the hose must show no leakage, burst or loss of pressure under those conditions.
Mandatory testing before shipment
- Hydrostatic test: normally carried out at 1.5 × working pressure.
- Fire test: mandatory for flexible lines and performed to the declared FSL.
- Functional test: performed on the complete assembly before shipment.
- Sour service: if the fluid contains H₂S, state it separately in the enquiry. Material requirements differ from standard service and are normally referred to NACE MR0175 / ISO 15156.
Shelf life and service life — the clause that costs money
Unlike most industrial items, a flexible choke and kill line is not something to hold in stock for years. Established industry practice is that storage beyond 6 months is not recommended, and the customary manufacturer warranty is around 18 months from dispatch, generally understood as 6 months of shipment and storage plus 12 months of service life.
The practical consequence for procurement: ordering early and holding the item as safety stock burns part of its usable life. Supply planning has to track the real drilling schedule.
What to put in the enquiry
To close a technical and commercial proposal in one exchange, specify:
| Item | Example |
|---|---|
| Working pressure (WP) | 10,000 psi |
| Nominal size | 3 in |
| Assembly length | 15 m |
| End connections | API 6A flange or Figure 1502 hammer union |
| Fire service level | FSL 2 or FSL 3 |
| Sour service | Yes / No (H₂S present) |
| Ambient service temperature | Minimum and maximum range |
| Documentation required | Pressure test report, material certificates, MTC |
Summary
Three clauses decide more than the rest when buying a flexible choke and kill line, and all three are routinely missing from enquiries: fire service level, sour service, and delivery schedule relative to shelf life. Stating them in the first request avoids a technical dispute at inspection stage and produces a more realistic price.
Related products in this family: BOP hose — Choke & Kill, well kill hose, well control hose and cementing hose. For the assembly end connections, see hammer unions.
Sources
The figures in this article were compiled and rewritten from the sources below. For design and purchasing decisions, always refer to the current edition of the standard itself:
1. API Specification 16C — Choke and Kill Equipment (American Petroleum Institute)
2. API SPEC 16C — scope and requirements (GlobalSpec)
3. Choke and kill line technical data to 10,000 psi (Abdex)
4. API 16C Choke & Kill Line (Pacific Hoseflex)
Need a quotation for a choke and kill line?
Send the working pressure, size, length, end connection and required FSL, and we will prepare a technical and commercial proposal.