Download Purging - Sellafield Suppliers

Nuclear Safety Element number 2 Local Administrative Controls
Procedures, method
statements, risk
assessments
Sellafield Ltd Projects Supplier Nuclear Safety Working Group-
012 Internal Purging
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What are the consequences of getting it wrong?
Excessive heat tint (oxidisation) can produce welds which may be weak, brittle, porous, sub standard and unacceptable to Sellafield Ltd
standards and specifications.
Welds exhibiting excessive heat tint (oxidisation) could result in failure resulting in a discharge of radioactive material into the environment.
Welds with exhibit excessive heat tint (oxidised) are virtually impossible to repair successfully resulting in welds being cut out.
Pipe to pipe welds which are cut out due to excessive heat tint (oxidisation) inevitably result in the loss of parent material which causes
problems with tie in welds.
Welds cut out which involve fittings may result in having to procuring replacement fittings.
3. Example:- AWS D18.2 Sample Numbers
4. What does good look like?
What does bad look like?
Nuclear
Safety
Tool
Box
Talk
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Why is it important?
The primary use of stainless steel is their general corrosion resistance.
Exposure to heat and oxygen during the welding process can severely reduce the corrosion resistance of stainless steel and results in what is
known as heat tint (oxidisation).
Shielding the weld during welding with an inert gas i.e. purging can prevent heat tint (oxidisation).
Inert gases which do not react with oxygen such as Argon or Helium or mixtures of the two create an oxygen free protective atmosphere
(purging) around the molten weld.
The new Sellafield ltd Engineering Standards state “it is the expectation that there shall be sufficient quality of purge media to achieve zero
discolorations”.
However it is appreciated that where line complexity is high or distance to purge access is high then zero heat tint will be difficult to achieve.
Sellafield Ltd Engineering Standards now make reference to AWS D18.2 – Guide to weld discolouration with the maximum allowed depicted
by sample 4 (100ppm oxygen in air).
Nuclear safety = realising the Design Intent through Quality of Workmanship in order
to protect our people and the environment