FULTON RBC1250 - Service Inspection of Welded Joints (UK Only)

RB-RBC-IOMM-2015-1
Fulton Ltd
Page 40
MAINTENANCE - 4
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ve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,speciesaminimumleveloftesting,
inordertoreducedowntimeduringtesting.RB/RBCboilersaretted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llet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.
4.10 SERVICE INSPECTION OF WELDED JOINTS (UK ONLY)