Wellhead Equipment Installation Requirements: Selection, Testing & Field Practice

Created on 10.27

What a Wellhead Assembly Does

A wellhead assembly is installed at the surface to control pressure and flow direction of oil, gas, and water, while sealing the annulus between each casing and tubing string. It typically includes a casing head, tubing head, BOP stack, cross, and associated branch piping.

Because the wellhead is the primary pressure-containment boundary, its installation quality directly decides well-control safety — not just equipment life.

1. Selection and Pressure Testing

The rated pressure of the wellhead must be driven by the maximum anticipated surface pressure from the fracturing or acidizing design — not by a generic "5,000 psi" label.

Selected equipment nominal pressure ≥ designed maximum surface pressure
Full assembly hydrostatic test before installation; only put into service after passing
Oil wells: tested to water-seal standard
Gas wells: tested to gas-seal standard
Always use new ring gaskets; inspect groove faces before makeup

Field rule: pressure rating is a system property, not a single tag on the flange.

2. Casing Spool Inspection and Makeup

The casing spool at the wellhead transition point must match the connected casing in material and specification.

Remove any fully annealed components from service — they no longer meet rated strength
Threads must be smooth, clean, and free of burrs
Test pressure reference: 80% of original manufacturer qualified test value
Verify bowl type, hanger type, and flange ring-groove compatibility before running
A small thread nick or reused ring gasket is usually the first link in a future SCP (sustained casing pressure) event.

3. Tubing Head and Christmas Tree Alignment

In typical production configurations:

A tapered tubing cross connects to a 7" bottom flange
Christmas tree mounts on the upper flange
Lift nipple on top flange for safe handling
Tapered male/female alignment ensures concentric seating
Annular groove between flanges houses a metal sealing ring (R / RX / BX per rating)

The tubing string lands directly into the upper flange. Alignment, not force, is what protects the seal.

4. High-Temperature and Steam-Injection Service

For steam injection and thermal wells, valve design matters as much as the spool body.

Dual-wing configuration with parallel gate valves
Body, bonnet, gate, and stem in creep-resistant alloy
Stable to 380°C under pressure cycling
Non-metallic seals in high-temperature compound
No deformation during open/close under thermal load

FUZER builds these assemblies with in-house forged bodies and CNC-machined ring grooves, so the sealing interface stays repeatable across thermal cycles.

5. Flange Makeup and Sealing Practice

Before final torque:

Clean flange faces and ring groove
Install new correct-size ring gasket
Hand-tighten studs, then lubricate as specified
Tighten in star pattern, 3 passes (30% → 70% → 100%)
After first pressure/temperature cycle, re-check bolt load
Skipping re-torque on HPHT wells is a common cause of slow flange weep.

API 6A wellhead assembly, casing spools and christmas tree equipment, FUZER oilfield wellhead compon

Why Specify FUZER

HEBEI FUZER TECHNOLOGY CO., LTD is a Shijiazhuang-based manufacturer of API 6A and API 16C wellhead equipment, with ISO 9001 certification and integrated forging, machining, and testing workshops. We supply casing heads, tubing heads, casing spools, crosses, and complete wellhead assemblies for:

HPHT and sour service
Steam injection / thermal recovery
Fracturing and acidizing programs
Onshore oil & gas fields
Every assembly is pressure-tested, NDE-inspected, and supplied with material traceability before shipment.

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