Boiler Inspection
There are two types of steam boilers. One is the fire tube, which is made from one combustion chamber and many tubes. The hot gases that are produced during the combustion process pass from inside the tubes and make a heat transfer with the water that is on the outside of the tubes.
The other type is a water tube steam boiler. It is just the opposite of the fire tube steam boiler; the water is in the inside of the tubes and the hot gases are on the outside of the tubes. In the fire tube boiler, we have a limitation on the combustion chamber diameter and length, and it cannot exceed a certain value. So for large-scale industry, generally the water tube boilers are used.
What is the Water Tube Boiler Inspection Requirements in the Manufacturing Shop?
The construction code for a water tube boiler is ASME Code Section I, and it covers the minimum requirements for design, materials, fabrication, inspection, testing, and preparation for initial delivery.
So this is when you require that your water tube boiler meet ASME Code requirements, or when you need your water tube boiler to be “S” stamped. For more detail about stamped boiler and requirements, review the Pressure Vessel Certification article. The regulation is similar to the one for the boiler. With the above explanation, your inspection and test plan (ITP) for the water tube boiler needs to meet the requirements of ASME Code Section I.
The water tube boiler is made from several components such as the HP Drum, finned Tubes, Headers, Tube Bundle, Stack, Damper, Silencer, Deaerator, etc. For more detailed information about water tube boiler shop inspection, review the following articles:
Third Party Inspection for Water Tube Boiler – Fabrication
When the Water Tube Boiler material inspection carried out and result was satisfactory or non-conformities closed by remedial action, then Water Tube Boiler manufacture will be authorised to start fabrication.
The third party Inspector checks following points on Water Tube Boiler based on the inspection and test plan (ITP) which is already agreed between purchaser and Water Tube Boiler manufacture.
The inspection scope is determined in ITP, some clients prefer to have stringent control and put the TPI inspector in more “hold points” in fabrication activities and some others may take lesser “hold points” and put TPI much more in the review document.
This depend to the inspection budget which client assign for inspection, much more inspection will have much more costs and less risks and conversely less more inspection will have less costs but more risks.
For more detail review Inspection and Test Plan for Water Tube Boiler article. There is draft ITP in this article which I believe it is the best practice for Water Tube Boiler inspection.
Third Party Inspection for Water Tube Boiler – Welded Drums and Headers Fabrications
The water tube boiler third party inspector does following inspection in mud and steam drums as well as headers:
Please note these components (Drums and Headers) in water tube boiler are similar to the pressure vessel, more detail information provided on Pressure Vessel Inspection Procedure article.
- Review welding procedures specification, procedure qualification records and welders performance qualification records
- Review welding map against welding procedures specification
- Inspect cut plate visually and dimensionally and paying particular attention to material identification marks and identifies material to be used for the test plates.
- Dimensionally inspect weld fit up and visually examine edge of weld preparation to ensure that they are free from defects which may affect the welded seam.
- Verify/witness NDE of weld preparation if required by code.
- Visually inspect all drum/header longitudinal and circumferential weld seams and review radiograph and ultrasonic test reports.
- Dimensional check on attachments and compensation plates, nozzles etc.
- Verify completion of welding to a satisfactory standard and review records of post weld heat treatment.
- Verify that all weld test plates have been completed and properly identified.
- Witness hydrostatic Testing
- Internal and external final visual inspection.
Third Party Inspection for Fire Tube Boiler-Fabrication
When Fire Tube Boiler material inspection carried out and result was satisfactory or non-conformities closed by remedial action, then Fire Tube Boiler manufacture will be authorised to start fabrication.
The third party Inspector checks following points on Fire Tube Boiler based on Inspection and Test Plan (ITP) which is already agreed between purchaser and Fire Tube Boiler manufacture.
The inspection scope is determined in ITP, some clients prefer to have stringent control and put the TPI inspector in more “hold points or witness points” in fabrication activities and some others may take lesser “hold points” and put TPI much more in the review document.
This depend to the inspection budget which client assign for inspection, much more inspection will have much more costs and less risks and conversely less more inspection will have less costs but more risks.
The fire tube boiler third party inspector checks following:
- Review weld procedure approval test and welder completency test records to ensure both are qualified in accordance with the code requirements.
- Check plate identities and compare with mill certification details.
- Witness the marking of test plates for identification before they are cut from the parent plate.
- Inspect weld preparations in shell plates and end plates after forming. Ensuring that correct test plates have been attached.
- As applicable to the welding method used in accordance with the boiler manufacturers quality plan visually inspect, Root runs on principal seams and plates, Completion of first side and back-gouged groove and After completion of all welding
- Examine results of non destructive testing and review radiographs.
- Witness required tests on previously selected test plates.
- Visually inspect tacked weld set ups on standpipes and similar attachments and review after completion of welding.
- Final visual examination after completion of all work including witness of hydrostatic test and internal/external examination. Review of heat treatment records.