Conducting Effective Visual
Inspections:
Mechanical Integrity for Refrigeration
Systems
Daniel Dettmers
Associate Researcher, IRC
What is an Effective Visual Inspection?
• Thorough inspection of the exterior of the
refrigeration system
– Insulated and uninsulated components
– Easily accessible and less than accessible components
– No drive-by’s
• What’s included?
–
–
–
–
–
Piping & valves
Vessels
Heat exchangers
Ammonia pumps
Etc.
Origin of the Requirement
29 CFR 1910.119 (j)(4)
– (j)(4)(i) Inspections and tests shall be performed on
process equipment
– (j)(4)(ii) Inspection and testing procedures shall follow
recognized and generally accepted good engineering
practices
– (j)(4)(iii) The frequency of inspections & tests of
process equipment shall be consistent with applicable
manufacturers‘ recommendations and good engineering
practices,
practices and more frequently if determined to be
necessary by prior operating experience
Good Engineering Practice?
• Manufacturers’ recommendations
• Industry standards
– ASME B31.5 or B31.3
• Pre-startup inspection
– NB-23 (National Board Inspection Code)
• Refers to ASME Boiler
& Pressure Vessel Code
• Guidelines
– IIAR Bulletin 109
– IIAR Bulletin 110
– IRC Mechanical Integrity Guidebook
• Currently in trial use
IIAR 109 & 110
109:4.7.3 – “Ammonia piping should be inspected…”
109:4.7.4 – “Uninsulated refrigerant piping should be
inspected…
110:6.4.2.1 - While the system is operational, the external
appearance of the surface of vessels or heat exchangers …
should be visually inspected weekly by the system
operating staff for any departures from normal.”
110:6.4.3 – “The external surface or the insulation and
associated vapor barrier applied to…vessels and heat
exchangers should be inspected no less than once every 12
months.”
IIAR 109 & 110
110:6.7.1 – “All uninsulated piping and associated
components…shall be inspected annually for any
damage or deterioration…”
110:6.7.2 – “At least as part of the annual piping inspection,
but preferably more frequently, the external condition of
the insulation and supports shall be inspected.”
• Additional components for yearly inspection in 110
– Ammonia pumps
– Shut-off valves
• 6 months for exposed stems
– Relief valves
Conducting the Inspection
• Establish a plan
– Identify and categorize equipment within scope of
1910.119 §(j)
– Establish prioritized list of appropriate inspections &
tests
– Conduct necessary tests and inspections within
prescribed frequencies
– Train all personnel –- consistent inspections
– Establish “go, no-go” criteria for continued service
– Document inspection and tests
Conducting the Inspection
• Assign inspection duties & timeframe
– Undesirable:
• All inspection duties fall on 1 person
• All inspections are planned for the day they are due
– Desirable:
• Diversify inspection duties
– Be certain inspection criteria is consistent
– Incorporate with other inspection/maintenance of valves, valve
tags, vessels, evaporators, etc.
– Involve new hires in process as part of OTJ training
• Plan inspection at least 1 month before due
• Train all involved and document their training
Potential Failure Mechanics
•
•
•
•
Which can we catch in a visual inspection?
No
Weld Failure
No
Stress Corrosion Cracking (SCC)
No
Internal Erosion
External Corrosion
Yes!
– Corrosion Under Insulation (CUI)
Almost
Corrosion
• “The deterioration of a material, usually a metal,
by reaction with its environment.”
- National Association of Corrosion Engineers (NACE)
• An anodic-cathodic reaction
– Positive ions travel through
an electrolyte (i.e. water,
ice, etc.)
– Material is sacrificed
• General (Uniform) Corrosion
• Pitting Corrosion
Corrosion
• Positive ions detach at the anode and
travel through a electrolyte (i.e. water, ice, etc.)
which acts as a carrier connecting to the cathode
the anode and cathodes need to be joined to
complete the circuit
– Anode => metal of the refrigeration system
– Cathode => metal of the refrigeration system
– Electrolyte => water
Controlling water is essential!!
Corrosion “Low Risk” Areas
• Uninsulated, painted pipe
– Easy to see any corrosion forming
• High temperature pipe
– If pipe is on the high side of the
system and insulated (i.e. HPL)
there aren’t large driving forces
pulling moisture into the
insulation system
Frozen
Insulation
• “Always Frozen”
– Ice is a poor electrolyte slowing
the corrosion process
– Be careful of what is defined as
“always frozen”
Wet
Insulation
Frozen
Pipe
Solid
Ice
Corrosion Under Insulation (CUI)
• CUI is general corrosion that occurs undetected
under piping insulation
– Water infiltrates the insulation system through a
break in the jacket/vapor barrier
– Insulation then becomes an enabler which aids in
corrosion by holding the water
tight to the pipe
– Pipe must also be without or
have a failure in the surface
protection (i.e. pipe paint)
Corrosion Under Insulation (CUI)
“Vapor Barrier”
Soaked Insulation
Pipe
Rust/Insulation
Inside Insulation
Outside Insulation
How Does Moisture Enter?
• Insulation system failures
– Breaches in jacket, vapor
retarder and insulation
– Travel under/through the
insulation from a breach
elsewhere in the system
• Water trapped at time of installation
• Diffusion of water vapor in the air
into insulation
– Driving forces pull moisture laden
air through cracks, holes and
unsealed joints
– Vapor retarder not barrier
Corrosion “High Risk” Areas
• Piping that is near to or above the
freezing point
• Piping that cycles temp (defrost
condensate)
• Piping that has circumferential
temp distribution (wet suction)
• Low points in the piping system
– Dips in line or end/corner of horizontal
run
– Bottom of vertical run
– Bottom edge of a horizontal pip run
• Piping that is hard to inspect
– under supports
– Behind walls/piping chases
Other Tell-Tale Signs
Biological Growth
External Frost
Especially in Summer
Corrosion
of the
Jacket
Wet Suction Returns
• Vapor sits in bottom of pipe
– Bottom always frozen
– Top can freeze-thaw
• CUI at mid-pipe or higher
• Look for bottom frost/water
Cross-section
Vapor
NH3
Ammonia Condensate Defrost Lines
80
• Large swings in
temperature
60
40
– Above and below
freezing (32oF)
20
– Large driving
0
force for moisture
– Multiple freeze/thaw cycles
that tear apart the insulation
2
4
6
8
10 12 14 16 18 20 22 24
Physical Impact
• Physical damage to insulation, pipe or vessel is usually
easy to spot
• Equipment susceptible to damage is often located in
areas of heavy traffic, outside (exposed to the elements)
or in an area subject to frequent clean-up wash downs
• Look anywhere fork trucks
can reach (and areas they can’t)
–
–
–
–
Behind guards
Ceiling hung evaps
Piping running up or along walls
Vessels in spaces
Documentation
1910.119 (j)(4)(iv) The employer shall document each
inspection and test that has been performed on
process equipment. The documentation shall identify
the date of the inspection or test, the name of the
person who performed the inspection or test, the
serial number or other identifier of the
equipment on which the inspection
or test was performed, a description
of the inspection or test performed,
and the results of the inspection
or test.
Questions?
• Innovation – Knowledge – Progress
www.irc.wisc.edu