Inspection of Tubes at Installation

Before installing new or reconditioned tubes, inspect the outside and inside surfaces for defects.

Determine the nominal wall thickness of the tube by gage measurement at the end. Check that tubes installed are satisfactory for the service in regard to thickness and material, and that tubes of specified materials and dimensions are installed in the proper locations. Be sure to record the necessary identifying information (thickness, lot or heat number, and material).

During installation of tubes, check that:
• Tube ends and headers have been cleaned and polished to remove all traces of mill scale and rust. Tube ends should be touched up just prior to rolling to ensure a clean joint.
• Headers and machined boiler drum openings are clean and that serrations are in accordance with specifications.
• A tube rolling procedure must be used to give the desired results. Tube rolling is becoming a lost art and this method of construction is being phased out; however, data are presented here in case they are needed.
– Proper records are kept (file in equipment folder).
– Tubes and headers are properly installed and secured to prevent movement.
– Proper tools and expanders are used.
– The rolling operation is carried out correctly without excess heating and that rolls are frequently cleaned and lubricated.
– Mechanics are furnished with calculated mandrel travel required to give desired expansion of tubes.
– Tubes are expanded until the tube is down in the header serrations (as checked with a feeler gage) without overrolling.
– Headers and header plugs are stamped with proper tube identification number to ensure correct installation.
– Welding and heat treatment of welded headers conform to approved procedures. Obtain heat treatment and hardness records.

After installation, inspect the rolled joint for tightness and cracks. When seal welded, inspect the seal welds for cracks, porosity, and undercutting. Take initial gage measurements of tubes and roll as required for the particular installation. Witness the hydrostatic test and inspect for leakage at the rolled joint and along the body of the tube.

The inspector should take the necessary tube and header measurements to calculate and provide the pin travel of the tube roll for the installation of new tubes or headers.

18. May 2018 by sam
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