In this module, you shall learn about the inspection aspects of API 611 – General Purpose Steam Turbines for Petroleum, Chemical, and Gas Industry Services
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.
Anchor bolts: attach the mounting plate to the support structure (steel or concrete)
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.
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.
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.
In case of conflict between this standard and the inquiry; the inquiry shall govern.
At the time of order; the purchase order shall govern.
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.
Each axially split casing shall be sufficiently rigid to allow removal and replacement of its upper half without disturbing rotor-to-casing running clearances.
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.
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.
The materials of construction of all major components shall be clearly stated in the vendor’s proposal.
The purchaser shall be notified before making a major repair.
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).
normal and maximum inlet steam temperature and pressure;
normal and maximum exhaust steam pressure; and
the purchaser’s equipment item number
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.
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.
Mill test reports is only required for the plates. It is not required for inventory items.
All forgings and bar stock for major rotating elements shall be 100 % ultrasonically inspected after rough machining
Supplier should submit the mechanical running test procedure to the purchaser 6 weeks prior to test for his review and approval.
Supplier shall notify purchaser 10 working days prior to mechanical running test for his witness.
If the operating temperature is different from hydrotest temperature, the hydrotest pressure shall be multiplied by the ration of material strength at the time of hydrotest divided by the strength of the material at the time of pump operation.
During mechanical running test, the contract seals and glands should be used, if this not possible, then, the contract seals and bearing shall be leak tested at least equal to MAWP prior to final assembly.
Prior to hydrotest and mechanical running test, all joints and connections shall be checked for tightness, and any leaks shall be corrected.
Due to no-load operation for extended periods of time during the test, the inlet steam conditions may need to be reduced to prevent overheating of the unit and exceeding design clearances.
Then, the speed shall be reduced to the maximum continuous speed and the equipment shall be run for 1 hour continuously.
Hydrodynamic bearings shall be removed, inspected, and reassembled after the mechanical running test is completed.
Equipment shall be prepared for the type of shipment suitable for six months of outdoor storage from the time of shipment.
Flanged openings shall be provided with metal closures at least 5 mm (3/16in.) thick, with elastomer gaskets and at least four full-diameter bolts.
Threaded openings shall be provided with steel caps or round-head steel plugs. In no case shall non-metallic (such as plastic) caps or plugs be used.
Lifting points and lifting lugs shall be clearly identified on the equipment or equipment package. The recommended lifting points shall be identified on boxed equipment.
During tender, vendor shall complete and forward the VDDR form to the client. Vender shall notify purchaser of any deviation.
The drawings indicated on the VDDR form (such as GA drawing, cross sectional drawing, schematics) shall be included in the proposal.
Vendor shall also note the list of components and materials used for each one (BOM or bill of material).
Vendor shall provide the guaranteed performance curves for power, flow and head.
Document deliverables shall be as per VDDR agreed between vendor and purchaser.
The vendor shall submit progress reports to the purchaser periodically as agreed.
Vendor shall include Installation, Operation, Maintenance, and Technical Data Manuals with the turbine at the time of shipment.
Annex A (informative) shows typical General Purpose Steam Turbine Datasheets.
Normally the purchaser would fill in the required output (flow, power, head) and the vendor would fill the rest.
Data sheet should be approved by the purchaser.
Annex B (normative) explain Dynamics (Information on Rotor dynamic Analysis). You do not need to study this annex for exam purpose.
Annex C (informative) shows typical Vendor Drawing and Data Requirements. The actual package could use this typical VDDR and tailor make it to project specific requirements including any additional test, material upgrade, etc.
Annex D (normative) Lubrication System Schematic (for info only, no exam question)
Annex E (normative) shows typical Procedures for Determining Residual Unbalance; look at the work sheet.
Annex F (informative) shows typical Inspector’s Checklist. This checklist comes handy for ticking boxes while inspecting the steam turbine.
Annex G (informative) explains Steam Turbine Nomenclature.
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