In 2009, a Minnesota-located refinery was experiencing through-wall leakage with several Class 300 rotary valves
tasked with controlling crude unit vacuum prefractionator charge heaters.
Maintenance personnel removed insulation from the valves and noted coke
residue on the surface of the valve bodies, which identified for them where the
leaks were occurring (Figure 1).
Fortunately, this particular situation
did not result in a safety event or a fire.
Instead, it illustrates how the refining
industry’s use of increasingly corrosive
feedstocks can combine with unknown
casting defects to cause potential valve
problems.
THE INVESTIGATION/
EVALUATION
Five valve body castings, all grade
CW2M (cast alloy C), were returned
from the refinery to the manufacturer
for evaluation using both nondestructive
and destructive tests.
The nondestructive tests performed
on the returned castings included visual
examination, pressure testing and liquid
penetrant (LP) examination.
Visual examination did not reveal
any signs of corrosion on the wetted
casting surfaces of the returned valves,
which included both as-cast and
machined surfaces.
The pressure testing used water at
1125 psig ( 7.76 megapascals or MPa)
followed by helium at 150 psig ( 1.0
MPa). LP testing was performed to the
requirements of ASTM A903 Level III,
which considers linear and rounded indications exceeding 3/16 inch ( 4. 8 millimeters) to be relevant. The helium and
hydrostatic water tests revealed no
leaks. Apparently, the hydrocarbon or
potential coking sealed the leak paths
once the valves were brought down to
ambient temperature and removed from
service.
LP testing of the castings revealed
indications on the exterior surface—a
lesser number of indications were on the
interior, cored surfaces. These indications were on both as-cast and machined
surfaces. Most of the LP indications
were shallow [<0.02 inch (0.5 millime-ters)] and removed with minor grinding.
AC & C
Pneum
TRIAC
• 100– 3
THD H
• 7,000
Stainle
Pinion
Rack & Pinion Actuator
180º P
Electr
WE/XE
• 500-2
• Single
• Integr
• On/O
Electric Actuator
• Optio
Sprin
• Weath
ATEX
• AWW
(513) 247-5465
FAX (513) 247-5462
e-mail: sales@a-tcontrols.com
www.a-tcontrols.com
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