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ASME B133.2-1977 — Basic Gas Turbine
📐 ASME (ANSI) B133.2-1977, “Basic Gas Turbine,” is the foundational technical volume of the ASME B133 family of gas turbine procurement standards. Final approval by the American National Standards Institute was granted on October 12, 1977; the document was developed by the ASME B133 Standards Committee on Procurement Standards for Gas Turbines, with ASME acting as secretariat. The standard does not prescribe how a gas turbine must be designed and built. Instead, it presents and describes the features that a user should specify in order to select a gas turbine that will yield satisfactory performance, availability, and reliability, so that competing proposals can be compared on a common basis and the unit can deliver what was promised over its design life.
The B133 family as a whole applies to open-cycle, closed-cycle, and semi-closed-cycle gas turbines with conventional combustion systems for industrial, marine, and electric power applications, and it covers the auxiliaries needed for proper operation. Explicitly excluded are gas turbines applied to earth-moving machines, agricultural and industrial tractors, automobiles, trucks, buses, and aeropropulsion units. For units using unconventional or special heat sources — chemical processes, nuclear reactors, furnaces, or supercharged boilers — the standards may be used as a basis, but appropriate modifications may be necessary. Within that family, B133.2 draws a deliberately narrow boundary: it is limited to the basic gas turbine, meaning the compressor, the combustion system, and the turbine. Generators, electrical equipment, auxiliary systems, and controls are addressed by companion volumes such as B133.5, B133.3, and B133.4.
💡 The B133 series is written in the language of procurement, not of design. It translates a user’s vague wish for a machine that is “reliable and easy to maintain” into clauses that can be quantified, verified, and written into a contract. B133.2 is the part of that language that covers the core engine.
1. Scope and Position of the Standard 📌
B133.2 is short, but almost every sentence points at something that has actually caused a trip, an outage, or a failure in service. Clause 2, “Gas Turbine — General,” establishes the overall quality principle: the design of the gas turbine, the selection of materials, and the manufacturing techniques employed shall be of a quality required by the application, so as to sustain mechanical integrity and deliver the expected performance and availability throughout the design life of the unit, with appropriate consideration given to maintainability. That single sentence pushes the definition of “fit for purpose” onto the user and the manufacturer jointly: the same machine built for peaking service and for base load does not warrant the same material and process requirements.
The remaining clauses walk through the engine component by component:
- Clause 3 — Rotating components (compressor and turbine). Rotors shall be mechanically designed to safely withstand transient speeds up to the turbine trip speed setting for brief periods at operating temperature. If field balancing is specified, the manufacturer shall state the method and the degree of disassembly required. Adequate provisions shall be made to control thermal bowing of the rotor after shutdown so that restart can be made without excessive vibration. All rotating and stationary blading shall be designed to prevent damaging fatigue stresses arising from aerodynamically induced excitation for the specified duty cycle. Vibration in the operating speed range shall not exceed the value specified by the manufacturer for that particular machine and duty cycle.
- Clause 4 — Compressor surge. The compressor shall be designed to avoid destructive surge during startup as well as throughout the operating speed and load range for the ambients specified by the user. Any operating restrictions required to avoid surge shall be specified by the manufacturer.
- Clause 5 — Combustion. Combustors and transition sections shall be designed with due regard to the designated fuels and to ease of maintenance. The combustor shell arrangement shall ensure correct alignment of the fuel nozzle in the chamber, components shall be arranged for simplified service or replacement, and nozzle parts in the gas path shall be positively locked against coming off in operation. Where dual-fuel or multiple-nozzle arrangements are specified, inactive nozzles and their supply systems should remain available for immediate use. Means for assuring and monitoring proper operation shall be specified, and the combustion system shall enable compliance with applicable emission standards.
- Clause 6 — Bearings. Bearing housing cooling shall be provided as required to minimize carbonization and deterioration of the lubricant. Bearings shall be designed to prevent instability at any operating speed, with the design verified by an appropriate stability analysis. Means for monitoring the condition of main shaft bearings should be specified. Proximity probes, if used, shall face a journal surface or a scratch-free surface concentric with the journal.
- Clause 7 — Seals. Seal design should minimize heat input to the shaft so as to avoid consequential bowing if rubbing occurs, shall permit easy removal and replacement at overhaul, and shall use materials compatible with the specified duty cycle and environment.
- Clause 8 — Casings. All pressure parts shall be suitable for the most severe coincident pressure and temperature expected; casing joints shall maintain minimum leakage throughout the service life; casings, supports, and expansion joints shall prevent injurious distortion from temperature, load, or piping stresses and shall maintain alignment with connected equipment. Jack screws, lifting lugs, eyebolts, or the equivalent shall be provided, and bolting and doweling shall be arranged for accessibility and to minimize seizure.
2. Technical Requirements at a Glance 📋
Translating those clauses into a procurement specification requires separating what the standard mandates from what the user may elect. The table below summarizes the focus of B133.2 by component, together with the items a purchaser will normally want to state explicitly.
| Component / system | Technical focus in B133.2 | What the specification should state |
|---|---|---|
| Rotor and blading | Transient overspeed to trip setting; aerodynamically induced blade fatigue; post-shutdown thermal bowing | Trip speed setting, turning/cooldown provisions, balancing method and degree of disassembly |
| Rotor dynamics | Lateral and torsional critical speed analysis of the combined driver–driven train | Allocation of responsibility: manufacturer when supplying the train, user when supplying the driver only |
| Vibration | Vibration within the operating speed range not to exceed manufacturer’s stated value | Measurement locations, alarm and trip thresholds, acceptance criteria, instrumentation standard |
| Compressor | Avoidance of destructive surge at startup and across the full operating envelope | Ambient range, bleed-valve or variable-geometry strategy, operating restrictions to be respected |
| Combustion system | Fuel suitability, nozzle alignment and locking, dual-fuel readiness, emissions compliance | Fuel specification (see B133.7), fuel-transfer time, emission limits and monitoring method |
| Bearings | Housing cooling, stability analysis, condition monitoring, probe target surfaces | Bearing type (tilting pad or rolling element), monitored parameters, probe type and count |
| Seals | Limiting heat input to the shaft, ease of overhaul, material compatibility | Seal type, allowable leakage, spare parts availability |
| Casings and supports | Pressure integrity at the most severe P-T condition, joint tightness, thermal distortion and alignment, borescope access | Horizontal split requirement, inspection port locations, jack screws and lifting lugs, OSHA-compliant insulation |
Among these, the allocation of the critical speed analysis is the item most often left ambiguous in negotiation and most expensive when it goes wrong. The standard is explicit: where the gas turbine manufacturer also provides the driven equipment, that manufacturer shall perform the lateral and torsional critical speed analysis of the combined system; where the manufacturer supplies the driver only, it is the user’s responsibility to see that such an analysis is performed. In real projects the compressor, gearbox, and generator frequently come from three different suppliers. If the contract does not pin this down, torsional resonance is typically discovered at first synchronization or first loaded operation — and correcting it then is far costlier than analysing it beforehand.
⚠️ On the overspeed clause: the requirement that the rotor safely withstand transient speeds up to the trip speed setting “for brief periods” is a minimum guarantee of mechanical integrity, not a licence to run near trip speed. Protection settings and mechanical design margins must be verified separately; “the standard allows it” is never a justification for relaxing an overspeed trip setting.
3. Maintainability as a Design Requirement 🔧
Maintainability appears repeatedly across B133.2, and it is given concrete form in Clause 8. The standard states that casings and ductwork should be designed to permit visual inspection of critical areas of the compressor and turbine blade path without major disassembly, with access through small removable covers and/or holes designed for the use of borescopes. The stated intent is to provide maximum inspection coverage of those areas with minimum disassembly. For peaking units and for machines burning heavy or contaminated fuels, this single clause largely determines the length of an inspection outage and whether borescope inspection can realistically be scheduled as routine maintenance.
The standard also requires jack screws, lifting lugs, eyebolts, or equivalent provisions to facilitate alignment, disassembly, and reassembly. Where jackscrews are used to part contact faces, they shall be designed to prevent damage to the joint surface, and bolting and doweling shall be arranged for accessibility and to minimize seizure. The manufacturer should indicate the maintainability features of the machine — compressor and turbine casings split on the horizontal centreline, modular disassembly, and so on. All casing connections should be designed with appropriate consideration for durability and maintainability, and insulation materials shall comply with OSHA regulations.
💡 A practical bid-evaluation technique: require each bidder to answer, in tabular form, whether the casings are horizontally split, whether a single blade row can be replaced without returning the rotor to the factory, how many borescope ports exist and which stages they reach, and what the heaviest lift is. These answers usually influence twenty-year operating cost more than a percentage point of efficiency.
4. Engineering Practice 🛠️
- 🔍 Start from the duty cycle. B133.2 references “the specified duty cycle” in the blading fatigue clause, the vibration clause, the seal material clause, and the standby-nozzle clause. A specification that does not state starts per year, load profile, annual operating hours, and ambient conditions gives the manufacturer nothing to commit to.
- 🔧 Turn “the manufacturer shall state” into a deliverable. Many clauses read “shall state” or “should indicate” — the field balancing method, the anti-surge operating restrictions, the bearing condition-monitoring means. These statements should be listed as contract deliverables in the documentation package, not left as verbal clarifications.
- 📊 Verify by test, not by promise. Mechanical running tests, overspeed tests, and the vibration baseline at first start should be written into the acceptance clause, with measurement locations, instrument accuracy, and pass/fail criteria defined up front.
- 📋 Mind the interfaces with companion volumes. B133.2 depends on B133.1 for definitions, B133.3 for auxiliaries, B133.4 for control and protection, and B133.10 for the prestructured information forms. Using the B133.10 forms as the backbone of the information exchange keeps the requirements from scattering across documents.
5. Frequently Asked Questions ❓
❓ How does B133.2 differ from B133.6, which also deals with performance?
B133.2 addresses the mechanical integrity and structural features of the core engine — rotor, blading, bearings, seals, casings. B133.6 defines how ratings and performance are stated, guaranteed, and tested. The first answers “is the machine robust and serviceable,” the second “how are power and heat rate defined and accepted.” They are meant to be used together.
B133.2 addresses the mechanical integrity and structural features of the core engine — rotor, blading, bearings, seals, casings. B133.6 defines how ratings and performance are stated, guaranteed, and tested. The first answers “is the machine robust and serviceable,” the second “how are power and heat rate defined and accepted.” They are meant to be used together.
❓ Does “avoid destructive surge” mean surge is never permitted?
No. The operative word is destructive: brief excursions to the surge boundary during transients are tolerated, but they must not damage blading, bearings, or seals. The manufacturer must state the operating restrictions required to avoid surge, and the user must carry those restrictions into the operating procedures and the control logic.
No. The operative word is destructive: brief excursions to the surge boundary during transients are tolerated, but they must not damage blading, bearings, or seals. The manufacturer must state the operating restrictions required to avoid surge, and the user must carry those restrictions into the operating procedures and the control logic.
❓ Why does the standard single out rotor thermal bowing after shutdown?
After a shutdown the upper and lower halves of the casing are at different temperatures. A rotor left stationary will bow, and the next start will show abnormal vibration, in the worst case leading to a rub. B133.2 therefore requires provisions — turning gear or a defined barring/cooldown procedure — so that restart can be made without excessive vibration. For units that start and stop daily this is critical.
After a shutdown the upper and lower halves of the casing are at different temperatures. A rotor left stationary will bow, and the next start will show abnormal vibration, in the worst case leading to a rub. B133.2 therefore requires provisions — turning gear or a defined barring/cooldown procedure — so that restart can be made without excessive vibration. For units that start and stop daily this is critical.
❓ B133.2 dates from 1977. Is it still applicable?
The B133 series has been progressively revised and partly withdrawn, and some volumes (for example B133.8 and B133.16) exist in much newer editions. For an executed contract, the edition referenced in that contract governs. For a new project, check the current ASME list of active standards and treat B133.2 as a technical baseline and checklist rather than the sole authority.
The B133 series has been progressively revised and partly withdrawn, and some volumes (for example B133.8 and B133.16) exist in much newer editions. For an executed contract, the edition referenced in that contract governs. For a new project, check the current ASME list of active standards and treat B133.2 as a technical baseline and checklist rather than the sole authority.
