Insulation, stress-corrosion cracking

Little information is available on the performance of copper and of copper alloys in contact with concrete, but concrete sometimes contains ammonia, even traces of which will induce stress-corrosion cracking of copper pipe. The ammonia may be derived from nitrogenous foaming agents used for producing lightweight insulating concrete. 

Where waterside deposits are evident, they provide a heat insulating effect and also permit under-deposit contaminant concentration. Under conditions of high pressure, heat flux, or stress, this combination of factors may lead to the development of embrittlement corrosion or stress corrosion cracking (SCC). 

Insulating materials exposed to stainless steel surfaces should be free of chlorides to avoid the phenomenon of stress corrosion cracking that can lead to system contamination and the destruction of tanks and critical system components. 

NACE studies determined that the most severe corrosion problems occurred under thermal insulation at temperatures between 140° and 250° F (60° to 120° C) where the temperatures were too low to quickly boil off any intruding water. At temperatures higher than the boiling point of water, other corrosion problems can occur. The intruding water can carry chlorides and other corrosive elements that can concentrate and result in stress corrosion cracking. [15]... 

Figure 19.7. Stress-corrosion cracking of 18-8, type 304 stainless steel exposed to calcium silicate insulation containing 0.02-0.5% chlorides, 100°C (250x). Note that the cracks for this environment start at a pit. An undulating path accounts for disconnected cracks as viewed in one plane [47]. (Copyright ASTM International. Reprinted with permission.)...

Control of halogen elements in materials (e.g. pipe insulation) in contact with stainless steel components should be ensured by design in order to avoid intergranular stress corrosion cracking (IGSCC). 

C 692 Method for Evaluation of Insulation (used to measure susceptibility to stress corrosion cracking)... 

Standard Test Method for Evaluating the Influence of Thermal Insulations on External Stress Corrosion Cracking Tendency of Austenitic Stainless Steel Standard Test Method for Electronic Measurement for Hydrogen Embrittlement fi-om Cadmium-Electroplating Processes... 

Extreme stress corrosion cracking (ESee) occurs when chlorides from the atmosphere, water leaks, or insulation concentrate on the surface of an 18-8 t)/pe stainless steel. Ferric ions from rusted steel flanges will aggravate the situation. ESCC is best combatted by coating vessels and piping over 4 in. using a zinc-free and chloride-free paint system. 

Avoid stress corrosion cracking under thermal insulation. 

The possibihty of stress corrosion cracking of austenitic stainless steels exposed to media such as chlorides and other halides, either internally or externally the latter can result from improper selection or application of thermal insulation. 

The type of corrosive environment responsible for brittle fracture of suspension composite insulators was established. A series of FTIR experiments was performed to identify chemical functionalities formed during the degradation process of composite insulators affected by brittle fracture. It was shown that the brittle fracture process was caused by the formation of nitric acid either outside or inside an insulator leading to stress corrosion cracking of the glass/polymer composite rod material. Nitrate was detected on the composite fracture surfaces inside a 115 kV suspension composite insulator which failed in service by brittle fracture. 17 refs. 

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