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ASME B16.34-2017 — Valves — Flanged, Threaded, and Welding End
⚙️ ASME B16.34-2017 is one of the most widely used valve standards in industrial piping. It establishes pressure-temperature ratings, minimum wall thickness, dimensions, tolerances, materials, marking, and pressure testing for valves with flanged, threaded, and welding ends. It covers gate, globe, ball, butterfly, and plug valves, sizes NPS 1/4 and larger, rating classes 150 through 4500, and is broadly referenced across the oil, chemical, power, and metallurgical industries. The 2017 edition was issued August 23, 2017, runs 242 pages, and supersedes the 2013 edition.
💡 B16.34, B16.5, and B16.10 form the “iron triangle” of valve standards: B16.34 sets body ratings and wall thickness, B16.5 the flange end dimensions, and B16.10 the face-to-face dimensions. Use all three together when specifying.
1. Scope and Framework 📌
This Standard applies to valves with flanged, threaded, or welding ends, in three categories: Standard Class, Special Class, and Limited Class valves.
- Standard Class valves: selected from the pressure-temperature rating tables of Section 2;
- Special Class valves: for service beyond Standard Class ratings, with additional examination per Section 8;
- Limited Class valves (Appendix V): where ratings are established from material allowable stresses by other rules.
| Section | Content | Key Points |
|---|---|---|
| 1 Scope | Valve types, end types, and rating classes | NPS 1/4 and larger |
| 2 Ratings | Pressure-temperature rating tables by material group | Tables 2-1.x, 2-2.x, etc. |
| 3 Nominal Pipe Size | NPS/DN correspondence | Per ASME B36.10 etc. |
| 4 Marking | Manufacturer, material, class, size | Traceability |
| 5 Materials | Applicable ASTM specification list | Table 1 |
| 6 Dimensions | Minimum body wall thickness, end dimensions | Tables and figures |
| 7 Pressure Testing | Shell test and backseat test | Shell test ≥ 1.5× rating |
| 8 Special Class | Additional NDE requirements | Appendices I–IV |
2. Pressure-Temperature Ratings and Material Groups 🔥
Ratings are the core of B16.34. Materials are grouped by similar allowable stress, and each group shares one rating table based on the lowest allowable stress in the group. Ratings are built on the material allowable stress at temperature, using the same basis equation as B16.5:
pt = C1 × S1 × Pr / 8750
where pt is the rated working pressure at temperature T, Pr the pressure class index, S1 the allowable stress at T, and C1 a units constant (C1=10 for MPa/bar, C1=1 for psi).
| Material Group | Typical Grades | Typical Applications |
|---|---|---|
| Group 1.1 (carbon steel) | WCB, WCC, A105 | General oil/gas, steam, water |
| Group 1.x (low temperature) | LCB, LCC, LF2 | Low-temperature and cold climate |
| Groups 1.13–1.18 (stainless) | CF8, CF8M, F304, F316 | Corrosive media, food, pharmaceutical |
| Group 2.x (alloy steel) | WC6, WC9, F11, F22 | High-temperature/high-pressure steam, hydrotreating |
| Groups 2.2–2.4 (Cr-Mo) | C5, C12, etc. | High-temperature sour and hydrogen service |
⚠️ As temperature rises, allowable stress falls and the permitted working pressure drops. Always check the rating at the design temperature, never the ambient rating alone; note the special provisions for Class 150.
3. Wall Thickness, Dimensions, and Marking 📏
Section 6 provides minimum wall thickness requirements for bodies and bonnets, depending on class, size, and material strength; Section 4 requires marking of the manufacturer’s name or trademark, material, pressure class, and nominal size for traceability. End dimensions (flanged, threaded, socket-welding, butt-welding) must conform to the companion standards.
💡 Minimum wall thickness may be computed by the basis equations of Appendix VI or taken from the class wall-thickness tables. For Special Class valves, radiography, magnetic particle, liquid penetrant, or ultrasonic examination per Appendices I–IV applies with stricter acceptance criteria.
4. Pressure Testing 🧪
- Shell test: not less than 1.5 times the 100°F (38°C) pressure rating (1.5 times design pressure for Limited Class), verifying body and bonnet strength;
- Backseat test: verifies the stem seal;
- Test medium: usually water (with corrosion inhibitor); gas testing only under controlled conditions.
🚨 When pneumatic testing high-pressure or gas valves, confirm the valve design permits gas testing, and strictly limit test pressure and site safety conditions — expanding gas can cause severe injury. Never let tests damage sealing surfaces or operating mechanisms.
5. Engineering Practice Essentials 🛠️
- 🔍 Selection workflow: design temperature and pressure → material group → rating table → class and size → end type → face-to-face and operating torque check.
- 🔧 Rating matching: flanged ends match B16.5 flanges, threaded ends per B1.20.1 taper pipe threads, welding ends per B16.25 butt-weld bevels.
- 📊 Acceptance testing: specify shell, seat, and NDE levels at purchase; request test reports and material certificates.
- 📋 Special Class: for very high pressure/temperature (e.g., supercritical steam), use Special Class valves with all additional examinations.
6. Frequently Asked Questions ❓
❓ Q: How do B16.34 and B16.5 ratings relate?
A: Both use the same rating-basis equation, but B16.34 rates the valve body and B16.5 the flange. The overall rating of a flanged-end valve is the lower of the body and flange ratings.
A: Both use the same rating-basis equation, but B16.34 rates the valve body and B16.5 the flange. The overall rating of a flanged-end valve is the lower of the body and flange ratings.
❓ Q: What is a Special Class valve?
A: Special Class valves serve pressure-temperature conditions beyond Standard Class tables; they require radiography, magnetic particle, liquid penetrant, or ultrasonic examination per Section 8 and Appendices I–IV, with stricter acceptance and higher cost.
A: Special Class valves serve pressure-temperature conditions beyond Standard Class tables; they require radiography, magnetic particle, liquid penetrant, or ultrasonic examination per Section 8 and Appendices I–IV, with stricter acceptance and higher cost.
❓ Q: How is the shell test pressure set?
A: 1.5 times the ambient rating for Standard Class valves; 1.5 times design pressure for Limited Class. Medium, pressure, and duration follow Section 7.
A: 1.5 times the ambient rating for Standard Class valves; 1.5 times design pressure for Limited Class. Medium, pressure, and duration follow Section 7.
❓ Q: Does B16.34 cover actuators and motor-operated valves?
A: B16.34 covers the valve itself, including manual handwheel operation. Electric and pneumatic actuators are outside its scope, but the assembled valve must still satisfy the Standard’s pressure-temperature and test requirements.
A: B16.34 covers the valve itself, including manual handwheel operation. Electric and pneumatic actuators are outside its scope, but the assembled valve must still satisfy the Standard’s pressure-temperature and test requirements.
7. Key Takeaways 📌
- Three valve classes: Standard Class (ratings per Section 2), Special Class (additional NDE per Section 8), and Limited Class (ratings per Appendix V) cover the full range of industrial service.
- Rating basis: body ratings derive from material allowable stress at temperature (same basis equation as B16.5); always read the rating at design temperature, and take the lower of body and flange ratings for flanged-end valves.
- Companion standards: combine B16.34 with B16.5 (flange ends), B16.10 (face-to-face), B16.25 (butt-weld ends), and B1.20.1 (threaded ends) for a complete specification.
- Testing rigor: shell test pressure is not less than 1.5 times the ambient rating; gas testing requires extra safety precautions.
- Material grouping: group numbers are based on similar allowable stress; groups not shown in B16.34 can be found in the material tables of ASME B16.5.
