Third Party Inspection for Steam Turbine - Procedure

The Third Party Inspection for Steam Turbine article provides a sample procedure for steam turbine inspection and testing in manufacturing shop and should be reviewed with steam turbine inspection and test plan.

This content guides you through all necessary stages in the production of the steam turbines, including the inspection of the material, casing hydrostatic testing, mechanical run test to the final inspection, preservation, packing, and dispatch to site.

You need to take this point into account: this article is written for a typical steam turbine and might not be detailed for special cases.

All steam turbine inspection and testing is done against the approved drawings, purchase order specifications, purchasers or company standards, and within the practices and rules of the country, state or province and any government decrees, laws, ordinance or regulation as may apply.

The applicable codes and specifications for a steam turbine that is under the construction process is:

  • Design code
  • Purchase order specification
  • Purchaser's standards
  • Approved drawings

and the applicable codes and standards are:

  • API 611/612
  • Other Related API Recommendation Practices

The applicable codes and standards may be based on other international standards such as JIS B8102, etc. This content is general and can be useful even if the design code is different from the API Code.

Required Documents for Third Party Inspector Review:

The list of documents normally is agreed upon in the Pre-Inspection meeting, which is held several weeks before the actual commencement of the inspection work.

The parties that participate in this meeting are the manufacturer, purchaser and third party inspection agency representatives.

These are the list of documents that are normally agreed upon to be presented to the inspector:

Third Party Inspection for Steam Turbine - Material Inspection

The first actual inspection work in the steam turbine is the materials inspection. The original or authenticated copies of mill certificates of material normally are available at the manufacturer's premises.

The third party inspector examines these certificates for compliance with specifications, and where appropriate, drawings.

The review includes checks on:

  • Certificate No.
  • Heat or Cast No.
  • Chemical Composition
  • Mechanical Properties
  • Heat Treated Condition
  • NDE Applied and Results
  • Surface Finish

Then the inspector witnesses the materials identification on the certificates against the materials marking. It is also necessary to check these with the steam turbine drawing datasheet, material list and other specifications as appropriate.

Visual inspection for surface finish and probable defects is done and dimensional compliance with specification need to be controlled, as well.

When third party inspector carries out the material inspection, then provides the inspection visit report (IVR), the report contains the following items:

  • Confirmation of satisfactory document review
  • Record of the endorsement of certification reviewed/witnessed
  • Record of all non-conformities
  • Record of any tests witnessed and the result

Third Party Inspection for Steam Turbine – Fabrication Inspection

When the steam turbine material inspection is carried out, and the results were satisfactory or non-conformities were closed by remedial action, then the steam turbine manufacturer will start fabrication.

The third party inspector checks the following points on the steam turbine based on the inspection and test plan (ITP), which has already been agreed upon between the purchaser and the steam turbine manufacturer.

Third Party Inspection for Steam Turbine

The inspection scope is determined in the ITP. Some purchasers prefer to have stringent controls and assign the TPI for more “hold or witness points” for inspection and test activities, and some others prefer less “hold or witness points” and assign the TPI much more work in the “review document.”

This depends in the inspection budget, which purchasers assign for inspection. Much more inspection will have a much larger cost and less risk, and conversely, less inspection will have less cost but more risks.

The third party inspector checks the following items in the steam turbine fabrication inspection process:

Third Party Inspection for Steam Turbine - Hydrostatic Tests

The Steam Turbine and other pressure containing parts are hydrostatically tested. The main items are:

  • Turbine casing
  • Steam chest
  • Emergency stop valves
  • Governor Valves

The third party inspector verifies that the correct test pressure has been applied to the relevant parts depending on specification requirements.

Third Party Inspection for Steam Turbine - Rotor Balance

When required by the contract or purchase order, rotor shaft assembly with the necessary half keys is subjected to a Dynamic Balance Check and is witnessed by third party inspector.

Third Party Inspection for Steam Turbine - Overspeed Test

When required by the contract or purchase order, the rotor shaft assembly is subjected to overspeed test and witnessed by third party inspector.

Third Party Inspection for Steam Turbine - Clearance Checks

After completion of fabrication, the required clearances are checked by third party inspector in accordance with the specification requirement in particular the following areas need to be examined:

  • Radial clearance between rotor and casing
  • Axial clearance between the rotor blades and stationary points

Third Party Inspection for Steam Turbine - Mechanical Running Test

When required by the contract or purchase order, the steam turbine is subjected to a mechanical running test and witnessed by third party inspector. Following items are taken into account for Steam Turbine mechanical running test:

  • Steam condition (temperature, flow rate)
  • Lubricating oil condition (viscosity, temperature, flow)
  • Cooling water condition (temperature pressure, flow)
  • Critical speed
  • Bearing temperatures
  • Vibration (Synchronous speed, Blade passing etc)
  • Operation of Sentinel valve
  • Operation of trip and throttle valve
  • Hand trip operation
  • Governor oil condition (temperature/pressure)
  • Noise level

Third Party Inspection for Steam Turbine - Governor Test

When required by the code, contract or order the governor test is witnessed by third party inspector. In particular the following characteristics are considered to be important:

  • Operation of overspeed trip emergency system usually by a consecutive 3 time test
  • Fluctuation of the Governor at rated speed
  • Governor rang

Third Party Inspection for Steam Turbine - Performance Test

The third party inspector witnesses the steam turbine performance test and following points are taken into account:

  • Satisfactory completion of previous tests
  • Power Output
  • Thermal Efficiency

Third Party Inspection for Steam Turbine - Final Visual Inspection

After completion of all testing a visual examination including a partial strip down of the unit is usually required by the specification and is witnessed by third party inspector. The particular areas of interest are:

  • Journal bearing pods
  • Thrust bearing pods
  • Rotor shaft with thrust collar
  • Shaft seal rings
  • Rotor blades
  • Tooth contact in gear trains

Third Party Inspection for Steam Turbine - Name Plate Controlling

The third party inspector checks the content in accordance with the approved drawings and specifications and make sure it is stamped in accordance with the code requirements.

Third Party Inspection for Steam Turbine - Painting and Coating

Surface preparation for painting is checked for the following points, according to specification by third party inspector:

It is necessary that surface condition is free from pin-holes, runs damage and other discontinuity

Third Party Inspection for Steam Turbine - Spare Parts, Loose Items and Accessories

Spare parts, loose items and accessories are checked visually for their dimensions, materials, workmanship and quantity, according to the purchase order specification.

Test marks and tags are checked for correct identification.

Third Party Inspection for Steam Turbine - Reporting:

The third party inspector provides an Inspection Visit Report (IVR) after each visit, as well as a final report summarizing the activities carried out during the steam turbine production in accordance with the contract requirements and circulated within the time limits specified in the contract.

The report is in the format required by the client and clearly indicates final acceptance or rejection of the steam turbine.

Third Party Inspection for Steam Turbine - Release Note:

When required by the contract or purchase order, a release note is issued by the third party inspection agency and given to the manufacturer when the steam turbines have been accepted.

Third Party Inspection for Steam Turbine - Packing, Marking and Shipping:

The following points are checked by the third party inspector:

  • All exterior machined surfaces are coated with rust preventative
  • All internal surfaces that are susceptible to corrosion are coated with rust preventative
  • All flanged openings are fitted with metal protectors in accordance with the specification
  • All threaded connections are provided with steel plugs
  • Exposed shafts and shaft couplings are covered with waterproof material and sealed
  • Check manuals and instructions are included to the specification requirements
  • Packing style and suitability for overseas shipment
  • Shipping marks and packing inspection
  • Pre-assembled systems are marked as required by the specification

Third Party Inspection for Steam Turbine - Final Book (Dossier)

The following final documents are reviewed and signed off by the third party inspector:

Manufacturer's data reports, Material certification, Dimensional record, NDE reports, Hydrostatic test reports, Rotor balance report, Clearance check report, Run-test reports, Performance test report, Final inspection report, Markings inspection report, Packing list, Spare parts list

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