Answer: A fully welded body normally has fewer external leak paths because it removes the large bolted body joint. A split body is easier to overhaul because technicians can open the body and replace the seats, ball, bearings and seals after the valve is safely isolated and removed from service. Fully welded valves are often preferred for directly buried gas pipelines. Split body valves are often more practical at accessible stations where internal repairs are expected.
Both designs can handle high-pressure natural gas. ISO 14313:2025 covers pipeline valves in ASME Classes 150, 300, 600, 900, 1500 and 2500, so body style alone does not decide the pressure class.[1] The correct choice depends on the installation, seat design, gas condition, pipe loads, repair plan, permitted shutdown and spare-valve availability.
This article mainly applies to large trunnion-mounted ball valves used in natural gas transmission. API Specification 6D defines manufacturing requirements for pipeline and piping valves.[2] API currently lists Addendum 3, issued in March 2025, for API 6D 25th Edition.[3]
Pressure Class Range
Split body and fully welded valves can both be supplied across common pipeline pressure classes. The exact size and pressure limits depend on the manufacturer’s qualified design, materials and testing.
| ASME Class | Split Body | Fully Welded Body | Main Selection Factors |
|---|---|---|---|
| 150 | Commonly available | Available | Installation access, cost and maintenance plan |
| 300 | Commonly available | Available | Valve size, end connection and seat design |
| 600 | Common in transmission service | Common in transmission service | Pressure integrity, pipe loads and outage plan |
| 900 | Design-dependent | Design-dependent | Body material, wall thickness, torque and testing |
| 1500 | Design-dependent | Design-dependent | Detailed design review and manufacturer qualification |
| 2500 | Specialized designs | Specialized designs | Materials, welds, seats, actuator torque and project approval |
Do not convert an ASME Class directly into one fixed working pressure. The allowable pressure also depends on body material and design temperature. ASME B16.34 covers pressure-temperature ratings, materials, dimensions, examination, testing and marking for new flanged, threaded, welding-end and certain flangeless valves.[4]
Body Construction
A split body valve has two or more main pressure-containing body sections. Studs or bolts hold the sections together. An O-ring, gasket or another static seal prevents gas from escaping through each body joint.
A fully welded valve joins its main body sections with permanent factory welds. The body cannot be opened by removing studs.
| Representative Body Design | Typical Bolted Main Body Joints | Permanent Main Body Welds |
|---|---|---|
| Two-piece split body | 1 | Usually none at the main split |
| Three-piece split body | 2 | Usually none at the main splits |
| Fully welded body | 0 | One or more, depending on body design |
The joint count above is representative. The actual number depends on the manufacturer’s construction. It also does not include stem seals, vents, drains, sealant fittings, pipeline flanges or field girth welds.
Body construction and pipeline end connection are different features:
- A split body valve can have flanged or butt-weld ends.
- A fully welded valve can also have flanged or butt-weld ends.
- A split body valve with butt-weld ends may still need to be cut out before overhaul.
- Butt-weld ends reduce the repair advantage of a split body, but they do not require a fully welded body.
See the detailed comparison of flanged and welded-end ball valves for the installation and maintenance differences.
Body entry type is also a separate choice. A side-entry valve is opened from the side or main split line. A top-entry valve is opened through a top cover. A top-entry design may allow technicians to remove internal parts without cutting the main valve body from the pipeline, but the line must still be isolated, depressurized, drained and made safe.
The practical differences are explained in this side-entry versus top-entry ball valve guide.
Manufacturing method must also be checked separately:
- A split body can use cast or forged body sections.
- A fully welded body can use forged, formed or fabricated sections.
- A forged valve is not automatically fully welded.
- A split body valve is not automatically cast.
When comparing quotations, keep the pressure class, bore, material, end connection, seat type, examination level and actuator package the same. Otherwise, the price difference may come from several design changes rather than the body construction.
Pressure Integrity
Valve integrity has three separate parts:
| Integrity Type | What It Means | Typical Failure |
|---|---|---|
| Pressure containment | The body, stem seals, fittings and connections keep gas inside the valve. | Gas leaks from a joint, stem, fitting or weld. |
| Isolation | The closed seats stop gas from passing through the valve. | The body remains sound, but gas passes through a damaged seat. |
| Operation | The valve reaches its required position under actual line pressure. | The actuator moves, but the ball does not fully close. |
A fully welded body mainly changes pressure containment. It removes the large mechanically sealed main body joint. It does not remove the stem, seats, actuator, vents, drains or pipeline connections.
A valve can therefore have a sound welded body and still leak through a damaged seat. It can also isolate the line correctly while releasing gas from a stem seal or drain fitting.
Fully Welded Body
The main benefit of a fully welded body is the removal of the large bolted body joint.
In a split body valve, line pressure creates a force that tries to separate the body sections. The studs must keep enough compression on the joint seal to prevent external leakage.
In a fully welded valve, the factory body weld carries this load as part of the pressure shell. There is no removable main body gasket or main body-joint bolt preload.
This design is useful for direct burial because:
- The buried body has fewer large mechanical joints.
- There are no exposed main body-joint studs.
- The external body is usually compact.
- A continuous coating is easier to apply around the main body.
- There are fewer joint crevices where water and soil can collect.
A fully welded valve is not maintenance-free. It still contains stem seals, seats, bearings, vents, drains and sealant fittings.
The valve may also contain two different weld categories:
- Factory body welds: join the main body sections during manufacturing.
- Field girth welds: connect the valve or its pup pieces to the pipeline.
A good factory body weld cannot correct poor field fit-up, excessive welding heat, unsupported pipe or installation misalignment.
Factory body-weld quality depends on:
- Correct base and filler materials
- Qualified welding procedures
- Qualified welding personnel
- Controlled preheat and heat input
- Controlled interpass temperature
- Post-weld heat treatment where required
- Hardness control for applicable sour service
- Nondestructive examination
- Dimensional checks
- Final shell and seat tests
The buyer should not accept “100% inspected” without more detail. The inspection plan should state:
- Which welds are examined
- Which test method is used
- How much of each weld is covered
- Which acceptance limits apply
- How repaired areas are re-examined
Useful manufacturing records include the weld procedure, welding qualifications, weld map, examination reports, heat-treatment records, hardness results where required and the location of any weld repairs.
Fully welded construction reduces large mechanical body joints. It does not make the buried weld easier to inspect after installation.
Split Body
A split body valve can meet the same pressure class as a fully welded valve when the body, bolting and joint seal are correctly designed.
The body joint works through bolt preload:
- The studs pull the body sections together.
- The gasket or O-ring is compressed.
- Internal pressure tries to separate the body sections.
- The remaining clamping force keeps the seal loaded.
- If the clamping force becomes too low, gas can escape through the joint.
Joint sealing can be affected by:
- Seal ageing or relaxation
- Temperature cycling
- Incorrect bolt lubrication
- Damaged threads
- Uneven tightening
- External corrosion
- Body-flange distortion
- Incorrect assembly after repair
Uneven tightening can leave one part of the joint under-compressed while overloading another area. It may also distort the body enough to affect ball, seat and bearing alignment.
Body studs are pressure-boundary parts. Replacement studs must match the approved material grade, diameter, thread, heat treatment, coating, temperature range and sour-service requirements.
A split body joint may be easier to inspect when the valve is above ground. Technicians can check for gas leakage, corroded studs, damaged coating, visible movement and previous repair work.
A leaking body joint should not be tightened under pressure without an approved engineering procedure. Changing the load on a live pressure joint can increase the leak or damage the sealing surfaces.
External Leak Paths
The U.S. Environmental Protection Agency identifies valves, connectors and open-ended lines as possible equipment-leak sources in the natural gas supply chain.[5]
The full installed valve must be checked, not only its main body joint.
| Leak Point | Split Body | Fully Welded Body |
|---|---|---|
| Main bolted body joint | Present | Removed and replaced by a factory weld |
| Stem seals | Present | Present |
| Vent and drain fittings | Present | Present |
| Sealant fittings | May be present | May be present |
| Flanged pipeline ends | Design-dependent | Design-dependent |
| Field girth welds | Present with butt-weld ends | Present with butt-weld ends |
A fully welded body reduces one major static leak path. It does not prove that the complete valve has low fugitive emissions.
Stem Leakage
The stem transfers torque from the actuator or gearbox to the ball. Because it passes through the pressure shell, it needs seals that retain gas while allowing the stem to rotate.
Stem leakage can be caused by:
- Aged or damaged seals
- Incorrect elastomer selection
- Stem scratches or corrosion
- Side loading from a heavy or misaligned actuator
- Rapid gas decompression
- Temperature changes
- Incorrect stem surface finish
- Repeated valve operation
A fully welded body does not remove this leak path.
ISO 15848-1 provides type-test procedures for external leakage from valve stem seals and body joints in hazardous or volatile service.[6]
The buyer should confirm:
- Primary and secondary stem-seal materials
- Blowout-resistant stem design
- Stem hardness and surface finish
- Fugitive-emission qualification
- Emergency sealing arrangement
- Whether stem seals can be serviced in the field
Vent, Drain and End Connections
Large trunnion-mounted valves normally have a body cavity between the two seats. Vent and drain connections allow controlled access to this cavity.
Small fittings can leak because of corrosion, damaged seats, loose threaded connections, vibration, impact, freezing or missing protective caps.
For buried valves, vent and drain extensions should be protected from vehicle impact, unauthorized operation, water entry, freezing and loss of identification.
Butt-weld ends remove flange gaskets and flange bolting, but field welding becomes part of the pressure boundary. The installation procedure should define:
- Maximum pipe mismatch
- Pipe support and fit-up
- Welding sequence
- Heat-input control
- Valve position during welding
- Nondestructive examination
- Post-installation testing
Factory pup pieces can move the field weld farther from heat-sensitive seats and provide pipe length for future valve replacement. See this valve end-connection guide for more selection details.
Seat Design
Most large gas-transmission ball valves are trunnion-mounted. Trunnions or bearings support the ball, while movable seat rings are pushed toward the ball by springs and pressure.
The differences from a floating ball design are explained in this trunnion-mounted versus floating ball valve comparison.
Body style does not decide seat performance. Split body and fully welded valves can use similar seat systems.
Important seat details include:
- Soft or metal sealing
- Seat-insert material
- Seat spring design
- Ball coating and surface finish
- Debris-control features
- Emergency sealant injection
- Cavity-pressure relief
- Single- or double-piston action
- Seat replacement method
Soft seats normally provide tight shutoff and lower operating torque in clean gas. Particles, excessive temperature, incompatible chemicals and rapid decompression can damage them.
Metal seats can better handle heat and abrasive particles in suitable designs, but they normally require harder surfaces, tighter manufacturing control and more operating torque. The permitted leakage rate must be stated in the purchase specification.
For severe service, see this metal-seated ball valve specification guide.
SPE, DPE, DBB and DIB
A single-piston-effect seat, or SPE seat, is normally pushed toward the ball by line pressure. If cavity pressure becomes higher than the pressure on the adjacent pipeline side, a correctly arranged SPE seat can move away from the ball and release excess cavity pressure to that side.
A double-piston-effect seat, or DPE seat, can be pushed toward the ball by pressure from either side. This can create another isolation barrier, but it may also prevent cavity pressure from releasing through that seat.
| Illustrative Pressure Location | Example Pressure |
|---|---|
| Upstream pipeline | 100 bar |
| Downstream pipeline | 0 bar |
| Normal body cavity | Near the connected line pressure |
| Heated trapped cavity example | 120 bar |
Illustrative example: If the adjacent pipeline remains at 100 bar but trapped cavity pressure rises to 120 bar, an SPE seat arranged for cavity relief may open a path back to the pipeline. A DPE seat may remain pressed against the ball, so another approved relief path may be needed. The 100-bar and 120-bar figures explain pressure direction only. They are not valve design limits.
The seat arrangement must be checked under three conditions:
- Upstream pressure is high and downstream pressure is low.
- Body-cavity pressure rises above line pressure.
- One seat is damaged or cannot seal.
Double block and bleed, or DBB, uses two seating surfaces that seal against pressure from opposite pipeline ends, with a method for bleeding the cavity between them.
Double isolation and bleed, or DIB, uses two defined isolation barriers against pressure from a specified source, with a method for bleeding the cavity.
Not every DIB valve uses the same seat arrangement. The buyer should review the seat drawing, pressure directions, cavity-relief method and individual seat-test procedure. The product name alone is not enough.
Internal Leakage
A valve can pass its shell test and still develop internal seat leakage during service.
Common causes include:
- Black powder
- Rust scale
- Sand or weld slag
- Cut or deformed seat inserts
- Scratched ball surfaces
- Failed seat springs
- Incorrect actuator stops
- Incomplete ball travel
- Heat damage during field welding
- Valve distortion caused by pipe loads
When a closed valve passes gas, use a clear check sequence:
- Confirm that the actuator completed its full travel.
- Check whether the indicator matches the drive position.
- Check pneumatic, hydraulic or electrical actuator supply.
- Compare operating time and torque with earlier records.
- Monitor body-cavity and downstream pressure.
- Test each seat separately where the design allows it.
- Review recent welding, cleaning or pigging work.
- Use sealant only when the valve design and site procedure permit it.
Sealant may temporarily close a small leakage path. It cannot repair a broken seat insert, failed spring, deeply scratched ball or incorrectly positioned ball.
Split body construction can make later seat replacement easier. Fully welded construction does not prevent seat damage from occurring.
Pipeline Loads
Pressure class covers internal pressure. It does not automatically define how much external pipe force or bending moment the valve can carry.
External loads can come from:
- Pipe bending
- Thermal movement
- Soil settlement
- Seismic movement
- Unsupported pipe weight
- Installation misalignment
- Field-weld shrinkage
- Actuator and gearbox weight
These loads may distort the valve without breaking the body. A small change in alignment can increase torque, reduce seat contact, overload bearings or apply side load to the stem.
A fully welded body is not automatically stronger against external bending. A split body is not automatically weaker. The buyer should request allowable pipe-end forces and moments and compare them with the pipeline stress analysis.
The actuator must also be checked against break torque, running torque and seating torque. See this valve torque curve guide for the main sizing terms.
Buried Installation
A fully welded body is often preferred for direct burial because it removes the large bolted body joint. This is a common preference, not an automatic rule.
A buried valve still needs:
- A suitable external coating
- Coating holiday testing
- Cathodic-protection compatibility
- A sealed stem extension
- Protected vent and drain extensions
- Ground-level operating access
- Soil-load and settlement checks
- A future excavation and replacement plan
Direct burial and installation inside an accessible valve chamber are different:
- For direct burial, fewer mechanical body joints normally have more value.
- For an accessible chamber, inspection and repair access may have more value.
The operator should determine the excavation size, lifting points, cutting length and replacement method before the valve is installed.
Repair Comparison
Valve work can be divided into four levels:
- Maintenance: inspection, leakage surveys and operation checks.
- Field repair: work on actuators, controls, fittings or permitted stem-seal parts.
- Workshop overhaul: opening the pressure body and replacing internal parts.
- Replacement: removing the complete valve and installing another unit.
Both designs normally allow field work on actuators, gearboxes, switches and external controls. The main difference appears when the ball, seats, stem bearings or internal seals need replacement.
| Failure | Split Body | Fully Welded Body |
|---|---|---|
| Actuator failure | Usually repaired externally | Usually repaired externally |
| Stem leakage | Depends on stem-seal design | Depends on stem-seal design |
| Main body-joint leakage | Requires isolation and joint assessment | No bolted main body joint |
| Seat damage | Normally repairable during workshop overhaul | May require specialist repair or replacement |
| Severe ball damage | Body can normally be opened in a workshop | Body cutting or complete replacement may be needed |
| Pressure-shell crack | Engineering assessment or replacement | Engineering assessment or replacement |
Split Body Overhaul
A typical split body overhaul includes:
- Isolate and depressurize the valve.
- Drain liquids and remove combustible gas.
- Remove the actuator and external controls where required.
- Remove the valve from the line if required by the design.
- Record operating torque and component positions.
- Separate the body using the approved bolt sequence.
- Remove and clean the ball, seats, stem and bearings.
- Inspect sealing surfaces and measure critical dimensions.
- Replace damaged parts and pressure-boundary seals.
- Reassemble using controlled bolt loading.
- Complete shell, seat and operating tests.
- Issue a repair report.
The ball should not be reused only because it looks smooth. The seat-contact area must be checked for scratches, pitting, coating loss, corrosion and dimensional damage.
Polymer and elastomer pressure-boundary seals should normally be replaced during major overhaul. Previously compressed seals may not provide reliable sealing after reassembly.
Repair may not be suitable when the body has an unacceptable crack, severe wall loss, permanent distortion, missing material records or dimensions that cannot be restored.
Fully Welded Valve Repair
Possible responses to a fully welded valve problem include:
- Emergency seat-sealant injection
- Permitted stem-seal work
- Actuator or gearbox replacement
- Removal and return to an approved repair facility
- Engineered cutting and rewelding of the body
- Complete valve replacement
Cutting and rewelding the body is not routine maintenance. Heat can affect material properties, seat alignment, internal seals, body dimensions, coating and original qualification records.
Any pressure-boundary repair needs an approved procedure, qualified welding, suitable examination, dimensional checks and post-repair testing.
Fully welded mainline valves are therefore often planned around complete replacement after major internal damage. This approach only works when a compatible spare valve, actuator, documentation and installation team are available.
Shutdown Cost
The repair-shop invoice is only part of the total cost.
A valve intervention may also require:
- Isolation of a long pipeline section
- Gas recovery or controlled venting
- Purging
- Excavation
- Heavy lifting
- Transport
- Cutting and field welding
- Nondestructive examination
- Leak or pressure testing
- Recommissioning
- Loss of transmission capacity
Total intervention cost = repair or replacement cost + isolation cost + gas-handling cost + field-work cost + lost-capacity cost + recommissioning cost.
| Illustrative NPS 24, Class 600 Case | Split Body Overhaul | Stocked Replacement Valve |
|---|---|---|
| Isolation, depressurizing and access | 12 hours | 12 hours |
| Removal or cutting | 12 hours | 8 hours |
| Repair, replacement or installation | 48 hours | 8 hours |
| Testing and recommissioning | 24 hours | 8 hours |
| Total illustrative outage | 96 hours | 36 hours |
Illustrative result: Under these assumptions, the stocked replacement shortens the outage by 60 hours. This does not prove that replacement is always faster. The result may reverse when no spare valve is available or when a qualified repair shop is nearby.
The example shows why a lower repair invoice does not always produce a lower total intervention cost.
Gas and Material Conditions
Gas composition affects the body, welds, bolting, seats and seals.
The valve specification should identify:
- Hydrogen sulfide
- Carbon dioxide
- Water and chloride content
- Minimum and maximum temperatures
- Maximum pressure
- Expected decompression rate
- Black powder and other solids
- Liquid carryover
- Methanol, glycol or compressor-oil exposure
ISO 15156-1 gives principles for selecting cracking-resistant metallic materials for H2S-containing oil and gas production environments and natural gas sweetening plants.[7]
For a welded body, sour-service checks should include the base metal, weld metal, heat-affected zones and repaired welds.
For a split body, the checks should also include body studs, springs, stems, trunnions and internal fasteners.
High-pressure gas can enter an elastomer. If pressure falls quickly, trapped gas can expand and damage the seal. Seal qualification should therefore match the actual gas, pressure, temperature and decompression conditions.
Black powder and liquid carryover increase the chance of internal seat and bearing damage. This makes repair planning more important, but it does not automatically require a split body.
Carbon steel, stainless steel and duplex options are compared in this API 6D ball valve material guide.
Factory and Repair Testing
Four types of verification should not be confused:
- Design qualification: tests a representative design.
- Production testing: checks the manufactured valve.
- Project testing: adds purchaser-specific inspection or tests.
- Post-repair testing: checks the valve after overhaul or body repair.
Useful material and manufacturing records include:
- Material certificates and heat traceability
- Positive material identification where specified
- Hardness results where required
- Welding and heat-treatment records
- Nondestructive examination reports
- Body-bolting records
- Seat and seal material identification
| Test | Data the Report Should Show |
|---|---|
| Shell test | Test medium, pressure, holding time and external leakage result |
| Seat test | Pressure direction, tested seat, pressure, holding time and measured leakage |
| Cavity-relief test | Cavity pressure, adjacent line pressure and the relieving seat or device |
| Torque test | Differential pressure, temperature, break torque, running torque and seating torque |
| Post-repair test | Repair scope, replaced parts, shell result, seat result and final operating torque |
Low-pressure gas testing can reveal small seat leakage paths that may not be clear during liquid testing. It does not replace the required hydrostatic shell test.
“Zero leakage” is unclear unless the test medium, pressure, holding time, measuring method and acceptance limit are stated.
Fire type-testing is different from routine production testing. ISO 10497:2022 covers through-seat leakage, external leakage, cavity-overpressure relief and valve operation under defined fire-test conditions.[8]
Common fire-test options are compared in this API 607 versus API 6FA guide.
Applicable Standards
| Document | Main Use | Useful Data |
|---|---|---|
| API Specification 6D | Manufacturing requirements for pipeline and piping valves | 25th Edition; current public update includes Addendum 3 |
| ISO 14313:2025 | Additional pipeline-valve requirements that supplement API 6D | Applies to Classes 150, 300, 600, 900, 1500 and 2500 |
| ASME B16.34 | Pressure-temperature ratings, materials, examination, testing and marking | Pressure rating depends on material and temperature |
| ASME B31.8 | Gas transmission and distribution piping systems | Covers pipelines, compressor stations and metering or regulation stations |
| Local regulations | Legal inspection, maintenance and operating duties | Requirements vary by country and pipeline type |
ASME B31.8 covers gas pipelines, compressor stations, metering stations and regulation stations.[9]
For covered U.S. transmission lines, 49 CFR 192.745 requires an emergency-related transmission valve to be inspected and partially operated at intervals not exceeding 15 months, but at least once each calendar year. It also requires prompt action when a required valve is found inoperable unless an alternative valve is designated.[10]
The contract should identify the required editions, addenda and purchaser options. Writing only “API 6D valve” does not define the body construction, seat arrangement, materials, testing level, actuator sizing or repair strategy.
Direct Comparison
| Selection Point | Split Body | Fully Welded Body |
|---|---|---|
| Main body connection | Bolted joint with a static seal | Permanent factory weld |
| Large body leak paths | Normally more | Normally fewer |
| Internal access | Easier during workshop overhaul | Difficult without specialist work |
| Seat replacement | Normally practical after disassembly | May require body cutting or full replacement |
| Direct burial | Possible with suitable joint protection | Often preferred |
| Accessible station | Useful when overhaul is planned | Useful when fewer body joints are the priority |
| Main manufacturing concern | Joint sealing and bolt loading | Weld quality and body alignment |
| Main repair plan | Workshop overhaul | Specialist repair or complete replacement |
| Effect on seat leakage | Body style does not decide seat performance | Body style does not decide seat performance |
| Main advantage | Repair access | Fewer mechanical body joints |
When to Choose Fully Welded
A fully welded body is usually more practical when:
- The valve will be directly buried.
- The installed body will be difficult to access.
- Reducing mechanical body joints is a project priority.
- The location is remote.
- Major internal failure will be handled by complete replacement.
- A compatible spare valve can be stored.
- Factory welding and inspection requirements are clearly defined.
- A compact external body and continuous coating are important.
When to Choose Split Body
A split body is usually more practical when:
- The valve is above ground or inside an accessible chamber.
- The valve can be removed without an excessive outage.
- Internal overhaul is part of the maintenance plan.
- A qualified repair workshop is available.
- Correct seats, seals and bearings are stocked.
- The owner plans to reuse the pressure shell.
- The main body joint can be inspected and protected.
Frequent operation does not make a split body more reliable. It increases wear on seats, bearings, stem seals and actuators. Split construction becomes useful when the owner plans to repair these parts instead of replacing the full valve.
Purchase Checklist
- Confirm whether the valve is split body, fully welded or top-entry.
- Confirm whether the body sections are cast, forged, formed or fabricated.
- Request a pressure-boundary drawing.
- Request the seat arrangement and pressure-direction drawing.
- Confirm how body-cavity pressure is relieved.
- Confirm whether each seat is tested separately.
- Verify body, bolting, ball, seat and seal materials.
- Define the pressure-boundary weld examination scope.
- Define the split-body bolt-loading procedure.
- Request allowable pipe-end forces and moments.
- Request the valve’s maximum required torque.
- Check actuator output at the lowest expected supply condition.
- Confirm whether internal parts can be replaced without cutting the body.
- Identify the approved repair facility and post-repair tests.
- Confirm spare-part availability and complete-valve delivery time.
Do not accept “maintenance-free,” “zero leakage” or “fire-safe by design” without test conditions and qualification records.
Maintenance Checks
A practical maintenance program should include:
- Stem and fitting leakage surveys
- Main body-joint or body-weld-area inspection
- Coating inspection
- Valve movement testing
- Operating-time and torque trending
- Actuator supply checks
- Position verification
- Vent and drain inspection
- Seat-leakage assessment
- Sealant-use records
For a split body valve, pay special attention to the main body joint, studs, coating and previous tightening history.
For a fully welded valve, pay special attention to the stem, small fittings, body-weld coating, field girth welds and the planned replacement route.
A partial-stroke test only proves that the valve can move through part of its travel. It does not prove full closure or seat tightness. Normal torque does not prove that the seats are leak-free, and a position indicator may be wrong if the coupling or drive train is damaged.
Conclusion
A fully welded body removes the main bolted joint and is often the better choice for directly buried or remote gas pipelines. A split body allows workshop access to the seats, ball and bearings, which is useful at stations with planned maintenance facilities. Both designs are available across API 6D and ISO 14313 pipeline classes, including Classes 150 through 2500, subject to manufacturer qualification. Compare body joints, seat pressure direction, allowable pipe loads, torque data, repair time and spare-valve availability. For covered U.S. transmission lines, emergency-related valves generally require inspection and partial operation at least once each calendar year, with no more than 15 months between checks.
