A problem for the petroleum and petrochemicals industry, RTJ flange stress corrosion cracking can also affect reactors, furnaces, tubes, valves and pipelines too.
Due to the high temperatures and pressure conditions machining is force to work in, it is natural for deterioration to occur - unfortunately corrosive materials can accelerate this process.
This results in groove cracks in a RTJ flange, but what can be done to resolve the issue? We take a look at some steps to delay and potentially avoid the damage entirely.
Finding the problem
As you will know, your current operations, dependent upon material you are transporting through pipelines, will be protected against potential corrosion anyway, therefore its important at the stage of identifying the problem to find out what the actual cause is.
Take into consideration the age and climate the RTJ flange operates in, as well as the job it serves. High stress concentration in the groove may be the simple explanation for the pipeline failure.
Look out also for inherent equipment stress by looking back through reports and maintenance reports. If these fail to materialise into an answer, the problem may just be caused by corrosion.
To avoid corrosion, RTJ flange and all grooves must be kept clean - this is the simplest solution.
Depending upon the material and contents, depends on what can be used to keep the flange clean. This will be clearly marked in your products' information pack.
It is not recommended to use any tool that may damage the surface of the flange. This includes any wire brush that may indent the surface.
You must also look out for external corrosion on the grooves as well as any damage that may effect performance.
A corrosion case study
The importance of checking your machine's information pack for maintenance tips cannot be over estimated, as this case study from Science Direct will show.
An RTJ flange used within the petrochemicals industry was found to have a high branch main crack in the base material. After deep inspection, the flange was found to have stress corrosion cracking (SCC) caused by the unknown presence of chloride in the system.
This was routed back to the use of an anti-seize grease used in the installation and maintenance procedure for the flange. The unqualified supply had damaged the flange to the point of replacement.
From the incident, the company in the case study moved to ensure all products used during maintenance were qualified for the machine. This was built into their future plans for high pressure stainless steal flanges.
When looking to care for all machinery and pipeline flanges, its important to first asses the product's chemical limitations. Prevention is certainly better than cure when it comes to stress corrosion cracking, just ensure you're using the write procedures for your equipment.
Photo Credit: Science Direct