Valve Comparison Guide
Welded Body vs Bolted Body Ball Valve: Which Design is Right?
Compare fully welded and bolted body ball valves: zero external leakage, maintainability, pigging, fugitive emissions ISO 15848, pipeline vs process plant applications.
Overview
A fully welded body (FWB) ball valve has no flanged body joints — the end caps and body are welded together as a single pressure-retaining shell. There are no body bolts and no external body joint gaskets that can leak. The only potential external leakage path is the stem packing. FWB ball valves are the standard design for oil and gas pipeline service (API 6D) because they eliminate all external body joint leakage, are compact and lightweight, and are compatible with pipeline pig passage.
DN50–DN1500 | Class 150–2500 | BW or socket weld ends | WCB, X65, SS 316, Duplex 2205 | API 6D, ASME B16.34
A bolted body ball valve has a split body (two-piece or three-piece) or a top entry body design where the internal components (ball, seats, stem) can be accessed by removing body bolts and separating the body sections. Bolted body valves are field-maintainable — seats and balls can be replaced in situ without removing the valve from the pipeline. They are the dominant design for process plant isolation valves where periodic maintenance and seat replacement are expected.
DN15–DN900 | Class 150–2500 | Flanged RF/RTJ or BW ends | WCB, SS 316, Duplex 2205 | API 6D (BW end), ASME B16.34
Pros & Cons
Fully Welded Body Ball Valve
Bolted Body Ball Valve
Fully Welded Body Ball Valve vs Bolted Body Ball Valve — Specification Comparison
| Parameter | Fully Welded Body Ball Valve | Bolted Body Ball Valve |
|---|---|---|
| Body Construction | Single-piece welded body — no external body joints; butt-welded end connections | Split body (2-piece or 3-piece) or top-entry — bolted body joint with gasket |
| External Leakage Points | Stem packing only — no body joint external leakage | Stem packing + body joint gasket(s) — multiple potential external leakage points |
| Field Maintainability | Not maintainable — full valve replacement requires pipe cut-out | Fully maintainable — seats, ball, and stem replaced in situ without pipe removal |
| Pigging Compatibility | Full-bore BW end — optimal for API 6D piggable pipeline service | Full-bore flanged — pigging possible with flanged connections; face-to-face slightly longer |
| Fugitive Emissions | Lowest — single stem packing leak path; ISO 15848 Class A achievable | Higher — body joint + stem; ISO 15848 Class B typical; Class A requires special low-emission body joint design |
| Buried Service | Standard for buried pipelines — coated BW ends, no buried bolt corrosion risk | Not preferred for buried — bolted joints and flange faces susceptible to buried corrosion |
| Replacement Cost | Full valve cost — no seat kit option; expensive for frequent service | Seat and ball replacement kit — 20–40% of full valve cost for routine maintenance |
| Body Joint Standard | No body joint standard — BW weld per ASME B16.25 | Body bolting per ASME B16.34, ASME B18.2 — bolts specified by pressure class and size |
| Weight (DN300 Class 300) | Lower — compact welded body without flange extensions | Higher — split body flanges and bolts add 15–25% weight vs FWB at same bore |
| Typical Service | Pipeline mainline isolation, buried valves, subsea isolation (API 6D) | Process plant isolation — refineries, chemical, power, water treatment (ASME B16.34) |
When to Use Each
Use Fully Welded Body Ball Valve when:
Use Bolted Body Ball Valve when:
Decision Guide
The choice between welded body and bolted body ball valves is primarily driven by two factors: (1) whether the valve will be in a piggable pipeline service requiring a BW-end fully welded design, and (2) whether the valve requires periodic in-situ maintenance. For all API 6D pipeline mainline isolation valves, piggable manifold valves, and buried pipeline isolation, specify fully welded body with BW ends — this is the industry standard and no other design is appropriate. For process plant isolation valves in refineries, chemical plants, and industrial facilities where the valve is in a flanged process piping system and seat maintenance is expected over a 20+ year plant life, specify bolted body (split body or top entry) with flanged ends — this allows economical seat and ball replacement during planned shutdowns. The fugitive emissions consideration increasingly favours welded body designs: ISO 15848 Class A (lowest leakage) is easier to certify with a welded body that has only one stem packing leakage point.
Frequently Asked Questions
What is a top entry ball valve and when is it used?
How does the body joint affect ISO 15848 fugitive emission compliance?
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