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ASME B40.100-2013 — Pressure Gauges and Gauge Attachments
📐 ASME B40.100-2013 is the comprehensive ASME standard for pressure-measuring instruments and their accessories, published by the B40 Standards Committee under the title Pressure Gauges and Gauge Attachments. It is a revision of ASME B40.100-2005 (R2011), issued on November 20, 2013, and approved as an American National Standard by ANSI on October 14, 2013. The Standard consolidates five sub-standards — B40.1, B40.2, B40.5, B40.6, and B40.7 — into a single volume with unified terminology, accuracy grades, general recommendations, safety, cleanliness, testing, and ordering parameters. It is among the most widely referenced ASME standards in the pressure gauge field and a key basis for instrument selection, procurement, and acceptance in the process industries.
💡 The core value of B40.100 is “one volume, complete coverage”: whether you procure elastic-element dial gauges or match them with diaphragm seals, snubbers, or pressure limiter valves, one standard defines accuracy, connection dimensions, and test requirements, greatly simplifying engineering administration.
1. Standard Structure and Scope 📌
The 2013 edition incorporates the five sub-standards as independent chapters. The body chapters 1 through 7 cover: Scope; Pressure Gauges, General; General Recommendations; Safety; Cleanliness; Pressure Gauge Testing; and Ordering Parameters and Related Standards.
| Sub-Standard | Content | Typical Application |
|---|---|---|
| ASME B40.1 | Pressure Indicating Dial Type Gauges — Elastic Element (analog) | General industrial pressure measurement; the ubiquitous pointer gauge |
| ASME B40.2 | Diaphragm Seals | Instrument isolation for corrosive, viscous, solids-laden, or hot media |
| ASME B40.5 | Snubbers | Pulsating services such as pump discharge; protect the Bourdon tube and steady the reading |
| ASME B40.6 | Pressure Limiter Valves | Prevent overpressure damage to instruments |
| ASME B40.7 | Gauges: Pressure Digital Indicating | Local digital display and remote signal transmission |
The scope of B40.1 is confined to analog, dial-type gauges that sense pressure mechanically through elastic elements and indicate it with a pointer moving over a graduated scale. The Standard does not include gauges of special configuration designed for specific applications, edge-reading gauges, deadweight (piston) testers, and similar categories.
⚠️ B40.1 does not cover every gauge type — electronic pressure transmitters, deadweight piston testers, and special-configuration gauges are outside its scope. Identify the product category and the applicable sub-standard before you specify.
2. Technical Requirements and Specifications 🔧
Accuracy grades: Table 1 of the Standard defines accuracy grades/classes with allowable error expressed as a percentage of the instrument span. Representative grades and their typical uses are shown below; refer to Table 1 for the authoritative values:
| Accuracy Grade | Allowable Error (% of Span) | Typical Use |
|---|---|---|
| 1A | ±0.5% | Calibration, laboratory, and high-accuracy applications |
| 1 | ±1.0% | Process control, precision indication |
| 2 | ±1.5% | General industrial process measurement |
| 3 | ±2.0% | Ordinary indication |
| 4 | ±3.0% | Coarse indication only |
Elastic elements: Figure 3 illustrates the C-type Bourdon tube (most common), helical Bourdon, diaphragm, capsule, and bellows elements; different elements suit different pressure ranges and media characteristics. Error evaluation covers not only basic error but also hysteresis and offset error — hysteresis is the difference between indications on the rising and falling pressure excursions at the same pressure point (Figure 10). Dials may be single-range or dual-scale (Figure 5). The Standard also defines retard gauges and suppressed-scale gauges (Figures 7 and 8): the former adds damping for observing pulsating values and instantaneous fluctuations, the latter raises the scale zero and enlarges a local interval for finer reading. Case types, mounting orientation, and recommended mounting dimensions are standardized in Figures 4, 6, and 9.
💡 “Accuracy” and “repeatability” are different concepts: accuracy measures deviation from the true value, repeatability measures consistency of successive indications. B40.100 accuracy grades are defined as a percentage of span; select the grade based on the operating interval of the measured pressure, not just the dial full-scale value.
3. Safety, Cleanliness, and Testing 🧪
Safety (Chapter 4): selection and installation must consider maximum possible pressure and overpressure scenarios to prevent the elastic element from rupturing and causing injury. The Standard gives explicit recommendations on overpressure protection, explosion-proof/protected case selection, and installation location; the accessories (diaphragm seals, snubbers, limiter valves) are themselves important means of improving safety.
Cleanliness (Chapter 5): Table 2 defines cleanliness levels. Gauges for oxygen and other oil-free services have strict limits on residual oil and grease; follow applicable references such as CGA G-4.1 and state the required cleanliness level at the time of ordering.
Testing (Chapter 6 and Mandatory Appendix I): test procedures for new gauge performance cover span error, hysteresis, zero return, repeatability, and overpressure tests. Mandatory Appendix II gives supplemental requirements for gauges used on regulators; Mandatory Appendix III lists supplemental ordering requirements (selectable item by item). Notably, the Nonmandatory Appendices A, B, and C of the 2005 edition were upgraded to Mandatory Appendices I, II, and III in this edition, and Appendix A was rewritten with new gauge performance criteria.
4. Engineering Practice Essentials 🛠️
- 🔍 Range selection: for steady pressure, operate between about 25% and 75% of span (commonly around two-thirds); for pulsating pressure, keep the operating point at or below about 50% of span and always reserve adequate overpressure margin.
- 🔧 Accessory matching: combine accessories by service — B40.2 diaphragm seals for corrosive/viscous/solids-laden media, B40.5 snubbers for pump pulsation, B40.6 limiter valves where overpressure risk exists, B40.7 for digital display and remote transmission; multiple accessories can be installed in series on one tap.
- 📋 Ordering parameters: specify range, accuracy grade, connection thread (e.g., 1/4″ NPT), case mounting type (bottom/back, axial/radial), dial size, and unit system per the Chapter 7 ordering checklist to avoid delivery mismatches.
- 🧼 Special media: for oil-free services such as oxygen, state the cleanliness level explicitly and request the cleanliness inspection certificate.
5. Frequently Asked Questions ❓
❓ Q: What are “span” and “range” selection?
A: Span is the difference between the upper and lower scale limits (e.g., a 0–10 MPa gauge has a span of 10 MPa); accuracy grade error is calculated as a percentage of span. Select the range from the process pressure, then choose the grade for the required accuracy, and finally verify connection and mounting.
A: Span is the difference between the upper and lower scale limits (e.g., a 0–10 MPa gauge has a span of 10 MPa); accuracy grade error is calculated as a percentage of span. Select the range from the process pressure, then choose the grade for the required accuracy, and finally verify connection and mounting.
❓ Q: What is the difference between grade 1A and grade 1 gauges?
A: Grade 1A allows ±0.5% of span, typically for calibration, laboratory, and high-accuracy use; grade 1 allows ±1.0% of span, suitable for general process control. Smaller grade numbers mean higher accuracy and higher cost — choose by need and avoid over-specification.
A: Grade 1A allows ±0.5% of span, typically for calibration, laboratory, and high-accuracy use; grade 1 allows ±1.0% of span, suitable for general process control. Smaller grade numbers mean higher accuracy and higher cost — choose by need and avoid over-specification.
❓ Q: Why can a snubber not be omitted in pulsating service?
A: Continuous pulsation cyclically flexes the Bourdon tube, causing fatigue and eventually rupture with media leakage, while the pointer vibrates too fast to read. A snubber (B40.5) damps pressure spikes into a smooth value and extends instrument life, but adds response lag — weigh protection against responsiveness when selecting.
A: Continuous pulsation cyclically flexes the Bourdon tube, causing fatigue and eventually rupture with media leakage, while the pointer vibrates too fast to read. A snubber (B40.5) damps pressure spikes into a smooth value and extends instrument life, but adds response lag — weigh protection against responsiveness when selecting.
🔍 Q: Is B40.100 mandatory?
A: No. ASME standards are voluntary, and B40.100 is no exception; however, once cited in a purchase contract or technical specification, it becomes a contractual technical condition, and the manufacturer must test and certify conformance to the Standard.
A: No. ASME standards are voluntary, and B40.100 is no exception; however, once cited in a purchase contract or technical specification, it becomes a contractual technical condition, and the manufacturer must test and certify conformance to the Standard.
