Vessel (CUI）Metal jacketing is used to protect against mechanical damages and weather conditions, and caulking/sealants are used in
addition for flashing of protrusions and overlaps.Due to several causes , water or moisture still gets in the insulation and will cause deterioration of thermal properties and start
corrosion (C.U.I.)

Even with high-quality metal jacketing and proper caulking/sealants, thermal cycling, wind loading, and aging inevitably break down flashing seals at protrusions (such as nozzles, brackets, and pipe supports) and overlaps. Once the barrier breaches, water creates a catastrophic feedback loop: it destroys the insulation’s thermal efficiency and rapidly accelerates Corrosion Under Insulation (CUI).

Your choice of hardware directly interrupts this failure mechanism by replacing a "sealed sponge" concept with a drainable air-gap design.

Material Performance Breakdown

For the system components you selected, the performance matrix under typical operational environments is as follows:

Component	Material	Key Properties & Selection Criteria
Vessel Spacers	PPS (Polyphenylene Sulfide)	High rigidity, exceptional dimensional stability, and excellent chemical resistance. Ideal for continuous operating temperatures up to 200°C–240°C. It prevents the insulation blocks from crushing or sagging over time.
	Silicone	High flexibility and excellent damping properties. Best suited for vessels experiencing heavy vibration or operational thermal expansion/contraction cycles. Typically rated up to 200°C.
	Stainless Steel	Ultimate structural load-bearing capacity. Impervious to chemical attack and suitable for extreme high-temperature or cryogenic applications (>250°C). Note: Must be paired with an isolation barrier if installed on carbon steel vessels to prevent galvanic corrosion.
Drainplugs	Engineered Black PPS	Highly robust, UV-stabilized (all-weather Black prevents solar degradation), and self-extinguishing (high flame retardancy) to meet refinery and chemical plant fire-safety standards (e.g., UL 94 V-0).

Mechanical Operation: How Spacers and Drainplugs Prevent CUI

By shifting from a completely tight insulation fit to a managed air gap, the hardware works in tandem to evacuate moisture:

    [ Metal Jacketing Breach at Protrusion/Overlap ]
                          │
                          ▼
             [ Moisture Enters Insulation ]
                          │
                          ▼
  ┌─────────────────────────────────────────────────────────┐
  │ 1. PPS/Silicone/SS Spacers create an open annular space │
  │    between the insulation and the vessel shell.         │
  └───────────────────────┬─────────────────────────────────┘
                          │ (Gravity Flow)
                          ▼
  ┌─────────────────────────────────────────────────────────┐
  │ 2. Liquid water tracks down the vessel walls through    │
  │    the spacer air gap instead of soaking the insulation.│
  └───────────────────────┬─────────────────────────────────┘
                          │ (Lowest Vertical Point)
                          ▼
  ┌─────────────────────────────────────────────────────────┐
  │ 3. Black PPS Drainplugs allow water to drain freely     │
  │    out of the outer jacketing while allowing air venting│
  └─────────────────────────────────────────────────────────┘

Breaking Capillary Action: The spacers separate the insulation block from the steel shell. This eliminates the "wicking effect" where wet insulation holds water directly against the metal surface.
Gravity-Driven Drainage Channels: The open space created by the spacers serves as an internal drainage track, directing all ingress water straight to the lowest gravitational points of the vessel.
Vapor and Liquid Ejection: Installing the high-strength, self-extinguishing Black PPS Drainplugs at the bottom of the outer jacketing allows liquid water to discharge freely. Additionally, these plugs facilitate ambient air movement, allowing the internal system to dry out naturally during thermal cycles.