Corrosion under insulation is a real threat to the onstream reliability of many of today’s plants. This type of corrosion can cause failures in areas that are not normally of a primary concern to an inspection program. The failures are often the result of localized and not general wasting over a large area.

Pembahasan – Muhajirin, Isya

Corrosion Under Insulation

Corrosion under insulation is a real threat to the onstream reliability of many of today’s plants. This type of corrosion can cause failures in areas that are not normally of a primary concern to an inspection program. The failures are often the result of localized corrosion and not general wasting over a large area. These failures can be catastrophic in nature or at least have an adverse economic effect in terms of downtime and repairs. The American Petroleum Institute code, API 570, Inspection, Repair, Alteration and Rerating of In-service Piping Systems, the piping code first published in June 1993, identifies corrosion under insulation as a special concern. Typically, as happened with API 653 and the Clean Water Act, the API codes become an industry standard, and the regulations demand that organizations maintain a program to meet that standard. OSHA 1910 is the rule that ensures the standard is met.
Corrosion under insulation is difficult to find because of the insulation cover that masks the problem until it is too late. It is expensive to remove the insulation, particularly if asbestos is involved. There are a number of methods used today to inspect for corrosion under insulation. The main ones are profile radiography, ultrasonic spot readings, and insulation removal. The other method now available is real time X-ray. Real time X-ray has proven to be a safe, fast, and effective method of inspecting pipe in plant operations.
The problem occurs on carbon steels and 300 series stainless steels. On carbon steels it manifests as generalized or localized wall loss. With the stainless pipes it is often pitting and corrosion induced stress corrosion cracking. Though failure can occur in a broad band of temperatures, corrosion becomes a significant concern in steel at temperatures between 0 and 149 ºC (32 and 300 ºF) and is most severe at about 93 ºC (200 ºF). Corrosion and corrosion induced stress corrosion cracking rarely occur when operating temperatures are constant above 149 ºC (300 ºF) (Kobrin and Moniz, 1993). Corrosion under insulation is caused by the ingress of water into the insulation, which traps the water like a sponge in contact with the metal surface. The water can come from rain water, leakage, deluge system water, wash water, or sweating from temperature cycling or low temperature operation such as refrigeration units.
Systems Susceptable to Corrosion Under Insulation
API 570 specifies the following areas as susceptible to corrosion under insulation: areas exposed to mist overspray from cooling water towers; areas exposed to steam vents; areas exposed to deluge systems; areas subject to process spills, ingress of moisture, or acid vapors; carbon steel piping systems, including those insulated for personnel protection, operating between -4 and +120 ºC (25 and 250 ºF). Corrosion under insulation is particularly aggressive where operating temperatures cause frequent condensation and re-evaporation of atmospheric moisture.
Other susceptable areas include: carbon steel piping systems that normally operate in-service above 120 ºC (250 ºF) but are in intermittent service; deadlegs and attachments that protrude from insulated piping and operate at a temperature different than the active line; austenitic stainless steel piping systems that operate between 60 and 204 ºC (150 and 400 ºF), as these systems are susceptible to chloride stress corrosion cracking; vibrating piping systems that have a tendency to inflict damage to insulation jacketing, providing a path for water ingress; steam traced piping systems that may experience tracing leaks, especially at the tubing fittings beneath the insulation; piping systems with deteriorated coatings and/or wrappings; locations where insulation plugs have been removed to permit thickness measurements on insulated piping should receive particular attention.

Tanya – Thurman S

Pak Isya,

Apakah sudah ditemukan cara untuk prevent corrososion under insulation ini.
Dan seandainya kita suspect ada corrosion under insulation, bagaimana tindakan
yang sebaiknya diambil dengan pertimbangan minimum impact kepada operasional struktur ?

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