The wellhead and Christmas tree are the primary pressure-containing barriers between the well reservoir and the surface environment. These critical assemblies control the flow of hydrocarbons, provide access for well intervention operations, and serve as the interface between downhole equipment and surface production facilities. A thorough inspection program for wellhead and Christmas tree equipment is essential for maintaining well integrity, preventing uncontrolled releases, and ensuring the safety of personnel working in the well area. This checklist covers the key inspection elements for both surface and subsea installations.
Why Wellhead and Christmas Tree Inspection Matters
Well integrity failures can have catastrophic consequences, from blowouts and uncontrolled hydrocarbon releases to environmental contamination and loss of life. The wellhead and Christmas tree are subjected to extreme operating conditions including high pressures, high temperatures, corrosive fluids, and cyclic loading from production operations. Over time, these conditions degrade seals, erode valve trim, and corrode metal surfaces. Regulations from BSEE, NORSOK D-010, and API standards such as API 6A and API 17D mandate regular inspection and testing of well barrier elements. Without a structured inspection program, operators risk missing early signs of degradation that could escalate into a major well control event. Proactive inspection not only prevents incidents but also extends equipment life and reduces the need for costly emergency interventions.
Master Valve Inspection
Master valves are the primary barrier valves on the Christmas tree. They provide the first line of defense for shutting in the well and must be maintained in fully operational condition at all times.
- Perform full-stroke function testing of upper and lower master valves to verify they open and close completely
- Check valve seat sealing by conducting a pressure test across each valve at the prescribed test pressure
- Inspect valve actuators for hydraulic or pneumatic leaks, correct operating pressure, and response time
- Verify that fail-safe close mechanisms are functional and valve closure times meet specifications
- Document valve position indicators and confirm they accurately reflect the actual valve position
Wing Valve and Swab Valve Inspection
Wing valves control the flow path to production flowlines and test manifolds, while swab valves provide access for wireline and coiled tubing operations. Both must function reliably under operating conditions.
- Function test all wing valves (production and kill wing) for smooth operation through full stroke
- Pressure test wing valve seats to confirm sealing integrity in both directions
- Inspect swab valve for wear, erosion, and correct operation of the bonnet seal and gate mechanism
- Verify that all manual valve operators, handwheels, and actuator connections are secure and undamaged
Wellhead Casing and Tubing Hanger
The wellhead housing, casing hangers, and tubing hanger form the structural and pressure-containing interface between the well casing strings and the Christmas tree. Their integrity is fundamental to well safety.
- Monitor annulus pressures on all casing strings (A, B, C annuli) and compare against historical values to detect barrier degradation
- Verify that casing annulus valves are functional and can be used for monitoring, pressure relief, or fluid sampling
- Inspect the wellhead housing and hanger packoffs for external leaks, corrosion, or mechanical damage
- Check lockdown mechanisms to confirm the tubing hanger is properly secured against pressure loads
- Review annulus pressure management records and confirm compliance with regulatory bleed-down and monitoring requirements
Seals and Gaskets
Seals and gaskets are the primary means of maintaining pressure containment at connections between wellhead and tree components. Their condition directly affects well barrier integrity.
- Inspect all visible metal-to-metal seal surfaces for scoring, corrosion, or erosion damage during maintenance or intervention activities
- Verify that ring gaskets (BX, RX, R type) are correctly installed and show no signs of extrusion, cracking, or deformation
- Check flange bolting for correct torque values, corrosion, and bolt stretch or relaxation
- Document seal replacement history and ensure spare seals and gaskets of the correct specification are maintained in inventory
Surface Safety System and Controls
The surface safety system (SSS) provides automated shutdown of the well in response to abnormal conditions. Its reliability is critical for preventing escalation of process upsets into major incidents.
- Test high-pressure and low-pressure shutdown sensors for correct setpoints and response to simulated conditions
- Verify surface safety valve (SSV) closure time meets API 14C requirements from initiation signal to fully closed
- Inspect hydraulic control lines, fittings, and junction boxes for leaks, damage, and corrosion
- Test the subsurface safety valve (SSSV) through full closure and leak testing at prescribed intervals
- Confirm that the emergency shutdown (ESD) system initiates correct valve sequences and alarms upon activation
Corrosion Monitoring and Chemical Injection
Production fluids often contain corrosive agents such as CO2, H2S, chlorides, and organic acids. Monitoring corrosion and maintaining chemical injection systems is essential for long-term equipment integrity.
- Review corrosion coupon data or corrosion probe readings from the wellhead and flowline area
- Verify chemical injection pump rates for corrosion inhibitor, scale inhibitor, and other treatment chemicals against prescribed dosages
- Inspect injection quills, check valves, and tubing connections for blockage, leaks, or erosion
- Check that produced fluid sampling and analysis is being performed at required frequencies to track corrosive species concentrations
Subsea Tree Specific Checks
Subsea Christmas trees present unique inspection challenges due to their underwater location. ROV-based inspection and remote monitoring are the primary tools for assessing subsea tree condition.
- Conduct ROV visual inspection of the subsea tree, tree cap, flowline connectors, and jumper connections for damage, marine growth, or debris
- Verify subsea tree valve positions through ROV observation and confirm alignment with control system indications
- Test subsea control module (SCM) functionality including valve actuation, sensor readings, and communication with the topside control system
- Inspect tree-mounted instrumentation including pressure and temperature transmitters for drift and damage
- Verify that the tree protection structure and guide frame are intact and provide adequate protection from fishing gear or dropped objects
Best Practices
- Establish a well integrity management system (WIMS) that defines inspection frequencies, test requirements, and escalation criteria for all well barrier elements
- Maintain a well barrier schematic for every well that clearly identifies all primary and secondary barriers and their current status
- Track annulus pressure trends over time and investigate any sustained or increasing pressures that indicate barrier degradation
- Integrate wellhead inspection data with production data analysis to correlate equipment condition with operating conditions
- Schedule tree maintenance and valve overhauls based on valve cycle counts, operating hours, and fluid corrosivity rather than fixed time intervals alone
- Ensure that personnel performing wellhead and tree inspections are competent and trained in well control fundamentals
How Checksheets Helps
Checksheets provides specialized digital inspection templates for wellhead and Christmas tree equipment that guide inspectors through every critical check point. The platform supports recording of annulus pressures, valve test results, seal conditions, and corrosion monitoring data with full traceability. Automated alerts notify well integrity engineers when annulus pressures exceed thresholds or when scheduled inspections are approaching. The dashboard view gives operators a fleet-wide picture of well integrity status across all their producing wells. Whether operating onshore or subsea, Checksheets ensures that wellhead and tree inspections are completed consistently, documented thoroughly, and acted upon promptly to maintain the highest standards of well integrity.