Discussion on Chloride Issues in Hydrostatic Testing and Insulation of Austenitic Stainless Steel Equipment
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The Code requires that during hydrostatic testing, the chloride content in water for austenitic stainless steel equipment shall not exceed 0.005%. Where does the basis for this come from? GB150 requires that chloride ions be no more than 25 mg/L during hydrostatic testing. According to the provisions in GB17393, the chloride ion content in many insulation materials is well above the limits set for these two values. So where does the basis for the limit on chloride content in hydraulic tests come from in the existing regulations? Does the chloride content requirement for hydrostatic testing in GB150 and pipeline codes conflict with the chloride content requirements for insulation? What is the connection between the two?
Also, the chloride ion concentration in the **standard circulating water has reached 200PPM. The material used for our heat exchange tubes is also 304 and 316; we’re puzzled by this as well.
The reason is to control chloride ions. It is simply to prevent intergranular corrosion of stainless steel caused by chloride ions. In fact, a brief pressure test has very little impact, so there’s no need to worry about whether it’s 0.005% or 25 mg/L; either way, it won’t be a problem.
**The standard (GB/T 5750-2006) specifies that the chlorine concentration in drinking water should be within the range of 5–100 μg/50 ml.
Small devices can be dried; the others can’t……
Chloride ions cause pitting or crevice corrosion in stainless steel, rather than intergranular corrosion.
I originally wanted to make changes. Chloride ions require three conditions for stainless steel: temperature, stress, and then chloride ions together with the stainless steel.
Chloride ions mainly cause stress corrosion cracking. Note that it is cracking; in terms of the microstructure, this manifests as intergranular corrosion. The presence of stress is also one of the necessary factors
I personally don’t agree with your view. Intergranular corrosion is different from Cl ion corrosion; intergranular corrosion represents a degradation of the material, while Cl ion corrosion is a type of corrosion, and the nature of the two is different. Stress corrosion cracking is another case, one that is more complex. For ordinary stainless steel sheets, they will still be corroded when placed in a Cl ion environment, and this has nothing to do with stress.