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Some D-Type Boilers were found to have
potentially dangerous cracks in welds
Purpose
This
Alert advises operators of D-Type water-tube boilers of 2 –
4.5 MW capacity to urgently check for the presence of cracks
in welds of these particular boilers. The cracks could cause a
failure of the boiler resulting in a serious risk to safety.
D-Type boilers of this size are commonly used in hospitals,
food processing and manufacturing
industries.
The
problem
Three D-Type
boilers were recently examined and substantial cracks were
found in the welds between the drum shell and both dished ends
of all three steam drums. The cracks in the circumferential
weld run in the transverse (drum axial) direction and extend
across the entire weld width and into the surrounding metal
(see Figures 1 and 2). The depth of the cracks has not been
established. However, in two boilers, cracks are believed to
be of substantial depth.
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Figure
1: General location of cracks |
Figure
2: Cracks in the steam drum to dish end
weld | Substantial cracks were also found in the toe of the
circumferential weld of the water-level chamber standpipe to
the drum shell. Cracks of this type could lead to rupture of
pressure components, possibly resulting in death or serious
injuries and substantial damage to
property.
The
particular boilers were manufactured in the late 1970s by an
interstate company.
Recommendations
Operators of D-Type boilers should conduct an
inspection of the weld areas in the steam drum of these
boilers in particular, as soon as possible. It is recommended
that Non-destructive Testing (NDT) methods be used to examine
the welds for any signs of cracking. In the case of any cracks
being detected, further NDT examination may need to be carried
out to determine the extent of the damage. Structural
integrity of the boiler would subsequently need to be
established by a competent person, prior to the boiler being
put back into service, unless the affected areas are
repaired/restored to the original design requirements.
Legal
responsibilities under the Occupational Health and Safety
Act
The Occupational Health
and Safety (Plant) Regulations 1995 place duties on employers to ensure that
plant is, amongst other things, inspected and maintained to
eliminate the risks associated with its use, or that the risks
are reduced so far as is practicable.
Regulation 702 in particular provides that,
when new or additional information about hazards relating to
plant or associated systems of work becomes available
(including the publishing of this Alert), an employer must
ensure that all hazards associated with the use of the plant
and the systems of work associated with the plant are
identified.
Although
the reasons for these cracks are not known, cracks in boilers
could be caused by the operating regime (cold starts –
frequency and temperature gradient during start-ups,
inadequate water quality – corrosion control and fouling,
etc.). Employers should adhere to manufacturer's (or
supplier's) recommendations and request further information if
there are any changes to be made to the use of the
plant.
When inspecting
boilers, the Australian Standard AS/NZS 3788 – 2001:
Pressure equipment –
In-service inspection
should be used for guidance. This Standard stipulates that the
respective areas should be examined for deposits, scale,
erosion, corrosion and any cracks.
AS/NZS 3788
provides guidance on the assessment and repair of defects. The
Australian Standard AS 4037
– 1999: Pressure equipment – Examination and
testing also provides
guidance on non-destructive examination methods of welded
joints, acceptance criteria, etc. to those concerned with
non-destructive examination of pressure
equipment.
Further
information
Code of Practice
Code of Practice for Plant -
July 1995.
Codes of
practice can be viewed and downloaded from the WorkSafe
Victoria web site www.workcover.vic.gov.au . Hard copies are available by emailing WorkSafe
publications at publications@workcover.vic.gov.au or by phoning 9641 1333. They can also
be obtained from Information Victoria - see contact details
below.
Acts & Regulations
Occupational Health and
Safety Act 1985
Occupational Health and Safety (Plant) Regulations
1995
Acts and
regulations are available from Information Victoria on 1300
366 356 or order online at www.bookshop.vic.gov.au . If you only want to view the
legislation you can use the Parliament of Victoria web site;
go to www.dms.dpc.vic.gov.au ,
click on "Victorian Law Today" and scroll down to the
"Search" window.
Standards Australia
AS 2593 – 2001: Boilers –
Unattended and limited attendance
AS/NZS 3788 – 2001: Pressure equipment –
In-service inspection
AS 1228 – 1997: Pressure equipment –
Boilers
AS 4037 –
1999: Pressure equipment and testing
Copies of standards can be obtained by
contacting Standards Australia on 1300 654 646 or by
visiting the web site at www.standards.com.au
The guidance on legal responsibilities in this Alert is
not intended to be a comprehensive evaluation of all of the
duties which may apply under the Occupational Health and
Safety Act given the subject matter of this
document.
| Alert 10/2002December |
This
document may be freely copied or reprinted. |
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