24 July 2003
including Change 1, Jan 2004 and Change 2, March 2005
Grooving, yet another type of flaw, is a metal deterioration caused by localized
corrosion and stress concentration. The inspector will examine all flanged surfaces,
particularly the flanges of unstayed heads, as thoroughly as their construction permits.
Grooving in the knuckles of such heads is fairly common since they have a slight
natural movement that causes a stress concentration.
Boilers with ogee or reversed flanged construction are also prone to grooving but may
not be readily accessible for examination. The inspector will insert a mirror through an
examination opening to examine as much area as possible. Other examination
methods, such as ultrasonics, may be employed. Since grooving is usually progressive,
its effect must be carefully evaluated and corrective action taken when it is detected.
Firetubes, watertubes, and piping are examined next. The fireside surfaces of tubes in
horizontal firetube boilers usually deteriorate more rapidly at the ends nearest the fire.
The inspector will check the tube ends for serious reductions in thickness. The surfaces
of tubes of vertical tubular boilers are more susceptible to deterioration at the ends
exposed to combustion. These exposed tube ends in the combustion space will also be
checked for serious reductions in thickness.
The inspector will thoroughly examine the waterside surface of all tubes for pitting and
corrosion. In vertical firetube boilers, excessive corrosion and pitting often occur at and
above the water level. Excessive scale on water surfaces must be removed before the
boiler is placed back in service.
Watertube surfaces will be carefully examined for corrosion, erosion, bulges, cracks, or
any evidence of defective welds. Tubes can become thinned by erosion produced by
the impingement of particles of fuel and ash at high velocity or by improperly installed or
operated soot blowers. Tube leaks frequently cause serious corrosion or erosion on
Fuel and ash also tend to lodge in restricted fireside spaces, as where short tubes or
nipples join drums or headers. Such deposits usually cause corrosion if moisture is
present. Coal and fuel oils contain sulfur, which is present in ash or soot deposits.
Dampness adds hydrogen and exposure to air adds oxygen. The result is H2SO4, not
helpful to metal surfaces. Clean this area thoroughly for the inspector's examination.
The inspector will thoroughly examine piping, connections, and fittings for leaks and to
ensure adequate provision for expansion and supports. Any leaks or other defects
must be corrected. To avoid water hammer, stop and drain valves must be located so
that water will not accumulate when the valves are closed. Excessive vibration and its
effects must be corrected.
All automatic low water fuel cutoff and water feeding devices will be examined for
proper installation. Operating instructions for the devices must be readily available.
The inspector will examine the float chamber type control devices for wear. Necessary
repairs must be made before the devices are placed back into service.
He will further check that fireside baffles in watertube boilers are in place. If proper
baffling is absent, high temperature concentrations often result, causing overheating in
portions of the boiler. The location and condition of combustion arches will be checked
to ensure flame impingement will not cause overheating. Any localized heat buildup