Fundamental of Boiler Field Inspection
Boiler tubes are normally routine inspected during scheduled maintenance outage and power plant overhaul. Sometimes they are also inspected when the boiler is shut down due to a failure or derating. Maintenance and inspection are always constrained by schedule. In this condition, there is required strategy to produce optimal inspection.
Pre Outage Preparation
Planning is key to project success. Inspector should prepare and review the following items:
- Review boiler document and drawing
- Review maintenance history data include past failure mechanism and work order
- Review previous inspection report, failure trends, and statistic.
- Review operation data include the policy on soot blowing and load management, abnormal boiler water, temperature, and fuel event.
- Review any potential failure in similar boiler type.
- Prepare checklist, procedure and inspection sheet.
- Prepare detailed schedule and workgroup.
Tube inspections are normally conducted when the boiler is out service and cooled. However, there are several potential hazards to deal with. Comply your plant safety procedure and maintain the safety awareness of all team member.
Always dispatch lesser-qualified inspector with experiences inspector with experience boiler inspector. In grouping, it is also best to collaborate between local and visiting inspector, spread the experienced team members for optimal coverage. Inspector should be grouped for efficiency and safety reason. The boiler inspection team leader should conduct a briefing to the team before an actual inspection occurs.
A Group of 400MW Boiler Inspection
Safety tools & equipment must comply requirement relevant to the inspection area include:
- Personal Protective Equipment (PPE): clothing, safety helmet, safety shoes, eye protection, mask, earplug.
- Climbing equipment: ladders, gondola lift, scaffolds, safety harness, ascender, fall arrester and kernmantle rope.
- Area and personal (headlamp) lighting.
- Air ventilation.
- Radio communication.
Inspection of boiler furnace/tube wall in simple overhaul, which the duration is short, usually conducted using gondolas lift. However, at the major inspection which has a longer duration, using scaffold is recommended to cover detailed inspection in all area.
Regarding to effectiveness and time constraint, proper tools must be prepared for field inspection.
- LCD Camera with telephoto capabilities, audio & video recorder and extra batteries. Today, millennials generation get easily for making vlogs, photography and other documentation with portable, durable and tough cameras.
- Inspection mirror, telescoping handles and pivot mounting are preferred.
- Material sampling tools: scrapper, screwdriver and bags or containers.
- Chisel hammer.
- Tape measure and flexible magnetic ruler for photo scale.
- Magnet to differentiate between carbon steel and stainless steel.
- Small level and plumb bob.
- Clipboard/book and pen.
Be careful not to lose equipment or tools that could plug ore damage boiler component during further operation. If something missing or drop, it can be time-consuming and costly to find. Always bring only the necessary tools to the inspection area. Secure loose item and use lanyards when necessary. Conduct pre and post inspection inventories of the tools and equipment.
The boiler inspection team leader should brief inspection team before the actual inspection be held. This usually occurs after the team has examined all of the documentation available at pre outage preparation. The team leader could notify the highlight information. This may include the inspection scope, schedule, leak history, replacement or upgrade material, special repair, and safety concern. This time also can be used to set inspection priority and repair criteria.
There are several tests conducted for boiler inspection. The most important is the visual test (VT). The other test is ultrasonic (UT) thickness test, magnetic particle test (MT), metallurgical test, etcetera, according to the scope of work. The visual test and any test may recommend another additional test when necessary to investigate any discontinuity.
Inspection note can be written on the inspection sheet. Inspection sheet should be standardized to make sure its traceability. The sheet should have minimum information including:
- Clear identification where inspection is taking place
- The element and tube number
- The relevant elevation which takes boiler landmark as a reference, such as a shoot blower, burner or manhole.
- The dimension of the discontinuity and required repair item
- Description of the required repair item.
Inspection documentation should be in good traceability. Photographic or audio-video recording should be taken include location reference. Comparative dimension should be included in the visual record by placing a tape measure or magnetic ruler. The photograph should be taken in close-up (focus) and wider view, which clearly shows the problem and the identification you have marked.
The discontinuity location may be marked with marking pen or spray paint (for a large area). If the sample is being taken, record the location from where the sample, mark the sample (or the sample container) and photograph the location from which the sample was obtained.
A written record should include the size, location, population (quantity) and condition/degradation description. Captions are very important as hundreds of pictures will be taken during the inspection.
Example The Photograph and Location Code on In-situ Metallography Test
Example Marking Paint and Location Code on UT Thickness Test
Post Inspection Briefing
After the team return from inspection field, the team leader should debrief them, to discuss the key point of the inspection. Through questions and discussions, the team leader will get insight relating to any non-conformance, which need to be countermeasure/repair within outage duration or next outage recommendation. The team leader also updates the planning and realization of the inspection scope. The team leader may adjust the inspection priorities related to work discovered. After the debriefing is complete, the team can prepare inspection reports.