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Proforma Safety, LLC
Proforma PSI…when
performance counts.
Faulty P91 Piping Ruptures; Kills and Injures Workers
Buyers beware! There have been critical failures associated
with P91 piping allegedly manufactured in China leading to several fatalities.
The piping was reported to have been used in a steam line from a 300MW unit
at the Datong Power Station Unit 2. After operating for less
than six weeks, the pipe ruptured, killing two and injuring
others.
The piping was allegedly stamped as being manufactured in the USA,
although actually manufactured in China. It made its way to Houston, where it was certified and shipped
to a fabrication company that supplied it for installation.
Grade 91 has been used in combined-cycle steam systems because
of its greater resistance to thermal fatigue and enhanced
creep strength compared to alternatives. However, Combined
Cycle Journal issued an industry alert in its first quarter
2005 issue, “Growing experience with P91/T91 forcing
essential code changes”, in which it warned:
“The
superior properties of Grade 91 depend entirely on the creation,
by heat treatment, of a precise condition of microstructure,
and the maintenance of this microstructure throughout its
service life. Specifically, the properties require the creation
and maintenance of a tempered martensitic structure, which
underpins the steel’s high tensile strength at elevated
temperatures and its high creep resistance.
“Failure
to obtain this precise microstructure during original steel
production, or any subsequent action that alters the microstructure
of the steel— such as the hot bending, forging, and
welding that regularly occurs during component fabrication,
plant construction, and steam-plant repairs—will seriously
degrade the alloy’s high-temperature properties. Making
matters worse, particularly for end users, is the fact that
this degradation in high temperature properties is not always
detectable with the standard QA tests.”
Reports are the Chinese Government has called for a formal investigation.
A discussion of details surrounding the case is available on
Eng Tips Forums.
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