In a mature field the wellheads and Christmas trees are often older than the people maintaining them. Equipment from several manufacturers, installed over decades, sits side by side, and some of those manufacturers no longer support the models in service. Keeping these barriers reliable depends on routine valve servicing and on having the right wellhead spare parts available when a seal or gate finally gives up. This article covers the maintenance tasks that matter most and how to build a spares plan around them.
Gate valve greasing and servicing
Most surface tree valves are API 6A slab or expanding gate valves. Their reliability depends heavily on lubrication. Body cavity grease protects the gate and seats from corrosion and trapped solids, and seat grease or sealant helps the gate-to-seat seal and reduces operating torque.
A sound servicing routine includes:
- Confirm isolation and bleed down according to site procedures before opening any fitting.
- Inspect grease fittings and their internal check valves; a leaking fitting is a pressure release point.
- Inject the grade of grease specified by the valve manufacturer, suitable for the service temperature and any H2S or CO2 present.
- Cycle the valve fully, count turns open and closed, and compare with the specified number of turns.
- Record operating torque, any leak-off, and the quantity of grease injected.
In hot UAE and GCC locations, grease that is too soft can wash out quickly, and valves that sit untouched for months tend to stiffen. A cycling and greasing interval set by service severity, not by calendar alone, works better.
Seat, gate and stem packing wear
Seat and gate damage is the main reason a valve fails its closure test. Common causes are sand erosion, corrosion pitting on the gate face, scale build-up and using a gate valve to throttle flow, which it is not designed to do. Turns-to-close that change over time, rising torque, or leak-off past a closed valve are early signs.
Stem packing leaks are the most frequent visible problem. Some designs allow packing to be energised or injected in service; others require replacement under full isolation. Many valves have a backseat, but whether it may be relied on during packing work is decided by the manufacturer's procedure and the operator's isolation rules, not by the technician on site. Replacement packing must match the valve model and temperature class; non-metallic seals are often the components that limit the valve's temperature rating.
Ring gaskets, hangers and pack-offs
API 6A flanged connections use R, RX or BX ring gaskets, matched to the flange type and pressure rating. RX and BX gaskets are pressure-energised and are generally treated as single-use: once they have been made up and broken, they should be replaced. Ring groove condition matters as much as the gasket. A pitted or damaged groove will leak even with a new ring, and groove repair or inlay is a workshop job.
Below the tree, tubing hanger seals, casing hanger pack-offs and secondary seals are barriers that are hard to reach. Leaks appear as pressure in an annulus or at a test port. Before planning a pack-off replacement, confirm the hanger type, the seal design, the test port arrangement and the back pressure valve (BPV) thread and profile. Tie-down or lockdown screw packing on the head flange is another common leak path that needs the correct kit for the head model.
Identifying legacy equipment
Ordering wrong-fit parts wastes weeks. Every spares request should rest on a confirmed identification record for each wellhead and tree, built from the nameplate, stamping and field measurement. The table below lists what to capture.
| Data point | Where to find it | Why it matters |
|---|---|---|
| Manufacturer and model | Nameplate, body casting, drawings | Internal parts are model-specific |
| Nominal size and working pressure | Nameplate, flange marking | For example 2-1/16 in or 3-1/16 in at 5,000 or 10,000 psi |
| End connection and ring groove number | Flange stamping, groove measurement | Determines R, RX or BX gasket and studs |
| Product specification level (PSL) | Nameplate, data book | Defines testing and documentation for the replacement |
| Material class | Nameplate (for example AA, DD, FF, HH) | Must suit H2S and CO2 partial pressures |
| Temperature class | Nameplate (for example L, P, U) | Seals and grease must match the range |
| Performance requirement (PR) | Nameplate, data book | PR1 or PR2 qualification level of the design |
| Serial number | Nameplate, body stamping | Traceability to original records |
Our guide to API 6A PSL, PR, temperature and material classes explains these markings. Where nameplates are missing or illegible, measure flange OD, bolt circle, bolt holes and ring groove dimensions and compare them with API 6A tables before ordering.
Building a spares matrix by criticality
Not every part deserves shelf space. Rank items by the consequence of failure and the lead time to replace them:
- Critical, long lead: complete master valves and wing valves for the most common size and rating, actuated surface safety valve bonnets or actuators, tubing hanger seals for the installed hanger types.
- Critical, short lead: stem packing, seat and gate kits, bonnet seals and grease fittings, held in larger quantities because they are used often.
- Consumables: ring gaskets, stud bolts and nuts, valve grease and sealant, test port fittings.
- Insurance items: spare tree caps, adapters and crossover spools for odd sizes, kept in low quantities where failure would leave a well shut in.
Link each line to the wells that use it. When a field has many trees of one model, the matrix tells you a few kits cover many wells; when a single legacy tree is the only one of its kind, it may be cheaper to plan its replacement than to stock parts for it.
Repair kit standardisation and documentation
Standard repair kits per valve model, size and class simplify ordering and reduce mistakes on site. Each kit should list every part number, the seal material and temperature rating, and the material class it is suitable for. Keep elastomer kits in cool, dry storage and track their age; seals in kits stored in hot yards degrade before use.
Documentation is the other half of the plan. New equipment is supplied to API 6A, with material test reports, typically to EN 10204 3.1, and pressure test records appropriate to the PSL. Equipment that is repaired or remanufactured should be handled under API 6AR, which sets requirements for repair and remanufacture of wellhead and tree equipment, so the returned item has traceable records of work done and tests performed. For sour service, confirm compliance with NACE MR0175 / ISO 15156.
Pre-shutdown maintenance checklist
- Identification record confirmed for each wellhead and tree to be worked on.
- Valve kits, packing and seals matched to model, temperature class and material class.
- New ring gaskets for every connection that will be broken, plus studs and nuts.
- Correct grease and sealant, and spare grease fittings.
- BPV or two-way check valve and running tools of the right size and thread.
- Test procedure and acceptance criteria agreed in advance.
- Documents requested: MTRs, test certificates and repair records.
Sending a wellhead spares RFQ
A good RFQ lists the identification data from the table above for each item, the quantity, required PSL, material and temperature class, the documentation needed and the delivery location. Photos of nameplates and flange stampings help resolve legacy equipment. We supply wellheads and Christmas trees, API 6A gate valves, RTJ gaskets and stud bolts and nuts. Send us your RFQ with the details and we will confirm fit and lead times.
Frequently asked questions
Can RX and BX ring gaskets be reused?
They are generally treated as single-use. Both are pressure-energised and deform on make-up, so a used gasket may not seal again. Replace them whenever a connection is broken and check the ring groove at the same time.
What is the difference between API 6A and API 6AR?
API 6A covers design, manufacture and testing of new wellhead and tree equipment. API 6AR covers repair and remanufacture of that equipment, including requirements for inspection, work records and testing of the returned item.
How often should wellhead gate valves be greased?
Follow the manufacturer's recommendation and adjust for service severity. Valves in sandy, sour or high-temperature service, or valves that are rarely operated, usually need more frequent cycling and greasing than the calendar minimum.
What if the original wellhead manufacturer no longer supports the model?
Build an identification record from the nameplate and field measurements, then look for compatible parts or engineered replacements that meet the same pressure, temperature and material class. For one-off legacy trees, compare the cost of stocking parts with planned replacement.