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Uniform or Localized Loss of Thickness

Terms in this set (96)

-All insulated piping and equipment are susceptible to CUI under conditions noted above even on piping and equipment where the insulation system appears to be in good condition and no visual signs of corrosion are present.
-Examples of locations where CUI can occur are listed below:
1) CuI can be found on equipment with damaged insulation, vapor barriers, weatherproofing or mastic, or protrusions through the insulation or at insulation termination points such as flanges
2) Equipment designed with insulation support rings welded directly to the vessel wall (no standoff); particularly around ladder and platform clips, and lifting lugs, nozzles and stiffener rings
3) Piping or equipment with damaged/leaking steam tracing
4) Localized damage at paint and/or coating systems
5) Locations where moisture/water will naturally collect (gravity drainage) before evaporating (insulation support rings on vertical equipment) and improperly terminated fireproofing
6) Vibrating piping systems that have a tendency to inflict damage to insulation jacketing providing a path for water ingress.
7) Deadlegs (vents, drains, other similar items)
8) Pipe hangers and other supports.
9) Valves and fittings (irregular insulation surfaces)
10) Bolted-on pipe shoes
11) Steam tracer tubing penetrations
12) Termination of insulation at flanges and other piping components
13) Insulation jacketing seams located on the top of horizontal piping or improperly lapped or sealed insulation jacketing
14) Termination of insulation in a vertical pipe
15) Caulking that has hardened, has separated, or is missing
16) Bulges or staining of the insulation or jacketing system or missing bands. (bulges may indicate corrosion product buildup).
17) Low point in piping systems that have a known breach in the insulation system, including low points in long unsupported piping runs
18) Carbon or low-alloy steel flanges, bolting, and other components under insulation in high-alloy piping systems
19) Locations were insulation plugs have been removed to permit piping thickness measurements on insulated piping and equipment should receive particular attention. These plugs should be promptly replaced and sealed. Several types of removable plugs are commercially available that permit inspection and identification of inspection points for future reference.
20) The first few feet of a horizontal pipe run adjacent to the bottom of a vertical run.
-An inpection plan should be structured and systematic approach starting with prediction/analysis, then looking at the more invasive procedures. The inspection plan should consider operating temperature; type and age/condition of coating; and type and age/condition of insulation material. Additional prioritization can be added from a physical inspection of the equipment, looking for evidence of insulation, mastic and/or sealant damage, signs of water penetration and rust in gravity drain areas around the equipment.
-Although external insulation may appear to be in good condition, CUI damage may still be occurring. CUI inspection may require removal of some or all insulation. If external coverings are in good condition and there is no reason to suspect damage behind them, it may not be necessary to remove them for inspection of the vessel.
-Considerations for insulation removal are not limited to but include:
1) History of CUI for the vessel or comparable equipment.
2) Visual condition of the external coverings and insulation
3)Evidence of fluid leakage e.g. stains
4) Equipment in intermittent service
5) COndition/age of the external coating, if applicable
-Common areas of concern in process units are high moisture areas such as those down-wind from cooling towers, near steam vents, deluge systems, acid vapors, or near supplemental cooling with water spray
-When developing the inpection plan for CUI inspection, the inspector should consider
1) Areas that are most susceptible to CUI. If CUI damage is found, the inspector should inspect other susceptible areas on the vessel.
2) Utilize multiple inspection techniques to produce the most cost effective approach, including:
--Partial and/or full stripping of insulation for visual examination
--UT for thickness verification
--Real-time profile x-ray (for small bore piping)
--Neutron backscatter techniques for identifying wet insulation
--Deep penetrating eddy-current inspection (can be automated with a robotic crawler)
--IR thermography looking for wet insulation and/or damaged and missing insulation under the jacket
--Guided wave UT
-Cooling water corrosion and fouling are closely related and should be considered together. Fluid temperature, type of water (fresh, brackish, salt water) and the type of cooling system (once-through, open circulating, closed circulating), oxygen content, and fluid velocities are critical factors
-Increasing cooling water outlet temperatures and or process side inlet temperatures tend to increase corrosion rates as well as fouling tendency.
-Increasing oxygen content tends to increase CS corrosion rates
-If the process side temperature is above 140F, a scaling potential exists with fresh water and becomes more likely as process temperatures increase and as cooling water inlet tempertures rise. Brackish and salt water outlet temperatures above about 115F may cause serious scaling.
-Fouling may occur from mineral deposits (hardness), silt, suspended organic materials, corrosion products, mill scale, marine and microbiological growth.
-Velocities should be high enough to minimize fouling and drop out of deposits but not so high as to cause erosion. Velocity limits depend on the tube material and water quality
-Low velocities can promote increased corrosion. Velocities below about 3 fps are likely to result in fouling, sedimentation and increased corrosion in fresh and brackish water systems. Accelerated corrosion can also result from dead spots or stagnant areas if cooling water is used on the shell side of condensers/coolers rather than the preferred tube side.
-300SS can suffer pitting corrosion, crevice corrosion and SCC in fresh, brackish and salt water systems
-Copper/zinc alloys can suffer dezincification in fresh, brackish and salt water systems. The copper/zinc alloys can suffer SCC if any ammonia or ammonium compounds are present in the water or on the process side
-ERW carbon steel may suffer severe weld and/or heated affected zone corrosion in fresh and/or brackish water
-When connected to more anodic material, titanium may suffer severe hydriding embrittlement. Generally, the problem occurs at temperatures above 180F but can occur at lower temperatures.