01362 691484
info@corrolesseastern.co.uk

Corrosion Under Insulation, Norfolk

THE PROBLEM

The existing carbon steel vacuum pipes had suffered from corrosion under insulation, resulting in the loss of wall thickness that necessitated there replacement.

What is corrosion under insulation?

Corrosion Under Insulation (CUI) refers to the hidden, localized corrosion that occurs on the exterior surface of piping, tanks, or other equipment that are insulated. This type of corrosion is particularly challenging to detect because it happens beneath the insulation material, making it a significant concern in industries like oil and gas, chemical processing, and power generation, where equipment is often insulated for thermal control, energy efficiency, or personnel protection.

Causes of CUI:

  1. Moisture Ingress: Insulation materials can absorb or trap moisture from rain, humidity, condensation, or leaks. This moisture can seep through gaps or breaches in the insulation or protective coating, leading to corrosion.
  2. Temperature Range: CUI typically occurs in a temperature range of about -4°C to 175°C (25°F to 350°F). Below this range, the water may freeze, and above it, water usually evaporates, reducing the likelihood of corrosion. However, this range is where water can remain in liquid form and cause corrosion.
  3. Type of Insulation: Certain types of insulation, especially those that are hygroscopic (absorb moisture), can exacerbate the problem by holding water against the metal surface.
  4. Environmental Factors: Harsh environmental conditions, such as high humidity, salty air, or industrial pollutants, can accelerate the corrosion process.

Consequences of CUI:

  • Structural Integrity: CUI can severely weaken metal structures, potentially leading to equipment failure, leaks, or even catastrophic accidents.
  • Economic Impact: The cost of repairing or replacing equipment damaged by CUI can be substantial. Additionally, downtime associated with inspection, maintenance, and repairs can be costly.
  • Safety Risks: Corroded equipment poses significant safety hazards to workers, including the risk of leaks, explosions, or fires, especially in environments dealing with hazardous materials.

THE SOLUTION

As requested we proposed a coating system for the protection of the newly installed sections of pipe.

Initially the new steel pipe once installed was cleaned by method of pressure washing, incorporating the use of an emulsifying degreaser. This was undertaken to ensure that any oils, greases and soluble salts were removed prior to preparation.

The effectiveness of this cleaning operation with regard to soluble salts was confirmed by the undertaking of a soluble salt test using the Bresle extraction method.

The new steel was supplied in Rust Grade A as per ISO8501-1 and therefore in accordance with industry standards and the manufacturers recommendations was prepared by abrasive blasting to SA2.5.

Pipework Painting 01
Pipework Painting 02

The surface profile of the steel following preparation was tested in order to ensure correct adhesion of the new protective coatings.

All surfaces were vacuumed clean and the effectiveness of this confirmed by the conduction of a dust tape assessment.

Given the pipes external location the first coat had to be applied as soon as possible after blasting and cleaning in order to ensure that the blast standard was not lost.

An initial coat of Hempel Hempadur 85671 was applied to achieve a nominal dry film thickness of 150 microns.

Pipework Painting 03

Following the application on an initial full coat in order to ensure that the preparation standard was not lost, a separate stripe coat was applied to all angles, edges and welds as per best coating practice.

Once cured a second full coat of the same material was applied in a contrasting colour as per best protective coating practice.

The cured coating was then checked for thickness and porosity using a low voltage wet sponge holiday tester. Any areas below thickness or porosity identified was marked prior to making good using the same protective coating material.

Pipework Painting 04
Pipework Painting 05