API Standard 611; General Purpose Steam Turbine(Optional)

Not part of Exam

In this module, you shall learn about the inspection aspects of API 611 – General Purpose Steam Turbines for Petroleum, Chemical, and Gas Industry Services

 

 

 

1 Scope

 

General-purpose turbines (API 611) can be horizontal or vertical turbines and are used to drive equipment that is usually used as spare and small in size or power, or is in non-critical service.

 

 

General Purpose Steam Turbines are used when steam pressure < 700 psi; temperature < of 750ºF or speed < 6,000 rpm.

 

Please note that special-purpose turbines (large power or size and used in critical service) are covered under API 612.

 

3 Definitions

 

Anchor bolts: attach the mounting plate to the support structure (steel or concrete)

 

Critical speed is when rotor is in a state of resonance or excessive vibration and chatter. It is the speed at which the natural frequency of the assembled rotor is reached at the operating speed.

 

The turbine operating range shall be well away from these critical speeds.

 

Hold down bolts (mounting bolts): are bolts that screw the turbine to the mounting plate which in turn bolted to the foundation (steel or concrete).

 

Hydrodynamic bearing: a low-clearance assembly that relies on a film of oil (and occasionally air) that develops space while the spindle is rotating.

 

The bearings transmit the load on self-renewing film of lubricant. The most basic hydrodynamic bearing is the journal bearing.

 

 

 

Maximum continuous speed ≥ 105 % of the highest operating speed.

 

Mounting plate is a base plate that the turbine would bolted and aligned.

 

 

Observed Point: An intervention point within Inspection and Test Plan (ITP) that the supplier/vendor notifies the client or purchaser to witness an activity that would proceed anyway, whether or not the client’s representative or inspector would attend.

 

Oil mist lubrication:  Bearing housing that is lubricated by a thin film of oil by compressed air.

 

Shall: A normative (mandatory) requirement; a must  in order to conform to the specification.

 

Should: recommended, non mandatory.

 

TIR (Total Indicator Reading):  Difference between the maximum and minimum readings of a dial indicator or similar device, monitoring a face or cylindrical surface, during one complete revolution of the monitored surface.

 

Trip Speed: The speed at which the turbine is shut down by an independent emergency overspeed device

 

Witnessed: Supplier/vendor notifies owner/client/purchaser to attend an Inspection and Test Plan (ITP) intervention point. It is a ‘hold point’ which means subsequent activities cannot be carried out unless the owner witness and approve this activity or waive it in writing.

 

Unit responsibility:  The responsibility for coordinating the documentation, delivery and technical aspects of the equipment and all auxiliary systems included in the scope of the order. It is normally the vendor/supplier/manufacturer.

 

5 Requirements

 

In case of conflict between this standard and the inquiry;  the inquiry shall govern.

 

At the time of order; the purchase order shall govern.

 

6 Basic Design

The General purpose steam turbine (including auxiliaries) covered by this standard shall be designed and constructed for a minimum service life of 20 years and at least three years of uninterrupted operation.

 

The vendor shall assume unit responsibility for all equipment and all auxiliary systems included in the scope of the order.

 

The equipment’s normal operating point will be specified on the datasheets.

 

All equipment shall be designed to permit rapid and economical maintenance.

 

Table 1 shows Design Criteria and Specifications for Cooling Water Systems

 

Sound Pressure Level (SPL) is normally measured in decibel and recorded at a distance of one meter away from the pump.

 

 

Fasteners should be at least 6 mm (1/4″) larger than the diameter of the bolt body.

 

 

Pressure casings shall comply with ASME Section VIII, Division 1 or Division 2.

 

Materials, casting factors, and the quality of any welding shall be equal to those required by ASME Section VIII, Division 1.

 

Manufacturing data report forms, third party inspections, and stamping as specified in the ASME Code are not required since pumps excluded from ASME VIII scope.

 

 

Each axially split casing shall be sufficiently rigid to allow removal and replacement of its upper half without disturbing rotor-to-casing running clearances.

Mounting surfaces shall be machined to a finish of 6 µm or better (for info only).

 

 

The depth of the tapped holes shall be at least 1.5 times the stud diameter.

 

Butt welded connections, size DN 40 (NPS 1 1/2) and smaller, shall be reinforced by using forged welding inserts or gussets.

 

Threaded connections shall not be seal welded because seal would mask leak.

 

 

Table 2 shows the surface finish for Flat and raised face.

 

All of the purchaser’s connections to the pump shall be accessible for disassembly without requiring any major part of the machine, to be moved.

 

Rotors shall be capable of operating without damage at momentary speeds up to 110 % of trip speed.

 

Shafts shall be machined from one-piece heat treated steel. Shafts with diameters ≥ 8” shall be forged.

 

Table 3 shows Bearing Selection

 

The materials of construction of all major components shall be clearly stated in the vendor’s proposal.

 

Weldable grades of steel forgings shall be repaired by welding using a qualified welding procedure based on the requirements of the pressure vessel code ASME Section VIII, Division 1, and ASME Section IX.

 

After major weld repairs, and before hydrotest, the complete forging shall be given a Postweld heat treatment to ensure stress relief and continuity of mechanical properties of both weld and parent metal.

 

The purchaser shall be notified before making a major repair.

 

The purchaser will specify the minimum design metal temperature and concurrent pressure used to establish impact test and other material requirements.

 

The vendor should exercise caution in the selection of materials intended for services between –30 °C (–20 °F) and 40 °C (100 °F).

 

A nameplate shall be securely attached at a readily visible location on the equipment and on any major piece of auxiliary equipment. Attachment pins shall be of the same material (austenitic stainless steel or nickel-copper). Welding is not permitted.

 

The following data, as a minimum, shall be clearly stamped on the nameplate in units consistent with the datasheets: (for info only).

 

vendor’s name;

 

serial number;

 

size and type;

 

rated power and speed;

 

first critical speed;

 

second critical speed;

 

maximum continuous speed;

 

minimum allowable speed;

 

overspeed trip setting;

 

normal and maximum inlet steam temperature and pressure;

 

normal and maximum exhaust steam pressure; and

 

the purchaser’s equipment item number

 

Anchor bolts are in the purchaser’s scope.

 

Lifting lugs attached to the equipment shall be designed using a maximum allowable stress of one third of the specified minimum yield strength of the material.

 

Instrumentation and Controls shall be designed and manufactured for use in the area classification (class, group, and division or zone) specified.

 

The primary function of the governing system shall be to maintain the turbine speed at a set value by regulating the steam flow through the turbine. It shall not allow the turbine to exceed the trip setting by 2%.

 

Table 4 shows Speed Governors class versus Maximum steady-rate speed regulation; Maximum speed rise; and Trip speed (110%-115%).

 

Instruments and Control Panels shall be completely assembled, piped and wired, requiring only connection to the purchaser’s external piping and wiring circuits.

 

The gages may be marked with the operating range or the operating range may be indicated on a tag next to the gage.

 

Table 5 shows the Minimum Requirements for Piping System Components

 

8 Inspection, Testing and Preparation for Shipment

The purchaser should specify the extent of participation in the inspection and testing through annotating his intervention point within the ITP; noting inspection requirement in the data sheet, etc.

 

The purchaser and supplier would agree on the amount of advance notification, witness points and inspection visits.

 

Prior to the purchaser witnesses the mechanical running or performance test, supplier shall confirm successful completion of the preliminary test.

 

The vendor shall supply the following data: MTR; examination and test records, any PWHT record; any QC test and inspection reports; any repair records; as built and running clearances.

 

Pressure-containing parts shall not be painted until the hydro test, leak test, NDE examination and inspection is complete.

 

Mill test reports is only required for the plates. It is not required for inventory items.

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Assembling a Turbine