Boiler Water Wall Tube Inspection — Digital Radiography During an Upgrade

A welding contractor in the power sector, specialising in upgrades to water-tube and steam boilers, was replacing a section of water wall tubing. The scope covered 160 welded joints made within the confined geometry of a membrane wall, against a fixed outage schedule. The key challenge was to carry out RT inspection of water wall tubes in a way that kept weld quality control from becoming the bottleneck of the entire upgrade.

The Challenge: An Outage That Costs Money

Upgrading boiler water wall tubes means working in a tight, densely finned geometry under time pressure. The tubes form a membrane wall, joined by webs, so access to each joint is restricted from every side. Every day of outage overrun translates into real losses for the operator of the unit.

With film radiography, the film has to go for chemical processing after exposure, and assessment of the joint follows hours later. Across a large number of welds this meant idle time for the welding crew, late detection of defects and the need to return to areas already closed out. Image quality was a further constraint: sensitivity too low for unambiguous assessment of fine discontinuities in thin-walled boiler tubing.

The Solution: Digital Radiography Instead of Film

We replaced the film technique with digital radiography (DR), carrying out radiographic testing to EN ISO 17636-2. The equipment comprised:

• a DÜRR DR 2430 DRC digital panel with 76 μm resolution,
• a COMET ECO 200ds X-ray tube with a 1.0 × 1.0 mm focal spot.

This combination translates into concrete benefits. A small focal spot limits geometric unsharpness, while the high resolution of the panel produces an image of markedly better legibility than film. The image appears on screen within seconds of exposure, so digital radiography does away with the darkroom, the chemistry and the film logistics. The result can be processed digitally on the spot, the area of an indication magnified, and the finding discussed there and then with the welding supervisor.

The Results: Wire W18 Instead of W14

RT inspection of the water wall tubes was completed faster and with higher sensitivity than the film alternative. The radiographs achieved visibility of image quality indicator wire W18, against W14 previously, in accordance with EN ISO 19232-1. A higher wire number denotes a thinner wire resolved on the image, and therefore better inspection sensitivity — in practice, detection of finer discontinuities and more reliable assessment of the joints.

Immediate on-screen review allowed welds to be assessed as work progressed, with any deviations corrected during the job — no waiting for a report, no returning to closed-out areas of the boiler. Defects found were repaired, and the repaired joints re-tested within the same outage. Under the film technique each such cycle — test, repair, verification test — would have meant two rounds of waiting for processing, and a real risk of delaying the return of the boiler to service.

All 160 joints were ultimately inspected. The client increased inspection throughput, held the outage schedule and received a complete set of digital documentation ready for archiving and handover to the plant owner.

We apply the same technique to production inspection — described in our case study on RT inspection of steel tanks.

Planning a boiler upgrade or membrane wall repair? Get in touch — we will set up inspection so that it does not extend your outage.