Service Inspection Of Welded Joints (Uk Only) - FULTON RB Series Installation, Operation And Maintenance Manual

MAINTENANCE - 4
4.10

SERVICE INSPECTION OF WELDED JOINTS (UK ONLY)

The requirement for in-service inspection of the main welded joints of the boiler is calculated by
the number of cycles since the last inspection.
Boilers running twenty four hours a day require the shell and furnace end plate welds to be
inspected at five year intervals and the longitudinal seam every ten years.
Boilers that are continually heated and cooled require more frequent inspection.
During manufacture the major longitudinal and circumferential weld seams are subject to non-
destructive testing by X-ray and/or Ultrasonic testing.
The boiler construction standard BS 2790 1992 class 1, specifies a minimum level of testing,
in order to reduce down time during testing. RB/RBC boilers are fitted with removable cladding
strips located above the main shell horizontal and circumferential weld seams. The purpose of the
in-service weld inspections is to check for:-
a) Buried defects during manufacture that are outside acceptable limits. Because the boiler was
100% tested during manufacture none should be found, and upon proof of 100% manufacture
testing these tests may be waived at the discretion of the 'competent person'.
b) Cracks propagating from the region of the toe of the fillet weld on the shell to the tube plate
weld, resulting from fatigue or corrosion fatigue cracking. These cracks would not be there
after manufacture but can develop in service, they are caused by stress due to a combination
of pressure loads, differential expansion, local temperature gradients, oxygen impurities in the
boiler water/steam and inadequate pH (water chemistry) control.
Differential thermal expansion and local temperature gradients all result from continuous
pressure/temperature cycling and heating from cold too quickly. Water treatment and in particular
oxygen corrosion are covered in Section 2.9 - Water Supply. The importance of correct water
treatment cannot be overemphasised.
To achieve long trouble free boiler life :
1. Maintain the boiler at working pressure as long as possible.
2. When heating from cold do so slowly.
3. Maintain water treatment within the prescribed limits at all times.
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Fulton Ltd
RB-RBC-IOMM-2015-1