As a Senior Integrity and Corrosion Engineer, Leonardo Araya has handled a wide variety of issues surrounding pipelines, tanks, and valves. Stainless Steel World Americas was excited to speak with Araya about the several methodologies that are used to assess a pipeline, and explore a few case studies involving valves and the mediation of corrosion in stainless steel and titanium tanks.
By Stephanie Matas and Sarah Bradley
Assessing pipeline integrity
The technical reports Araya prepares address any areas of jeopardized integrity along the pipeline. He mentioned there are three distinct methodologies used to assess the integrity of a pipe.
Hydrostatic testing is a process in which piping systems, pressure vessels, and gas cylinders can be assessed for strength and leaks. These tests cannot be conducted while the component is in service, nor can they offer continuous monitoring of the equipment for leaks after the test is completed. Components often require hydrostatic testing after a shutdown or repair has been completed in order to validate the equipment that is being placed back in service. For the hydrostatic testing method, water is put into a pipe and pressure is applied; if the pipe breaks it is considered faulty.
In-line inspections evaluate the integrity of a pipe or pipeline using ‘smart pigs’ to detect internal damage and irregularities such as corrosion, deformations, and cracks. Intelligent pigging can be done on many types of pipeline sizes without the need to stop the flow of materials. An inspection pig is loaded into a receiver at a valve or pump station that is specially configured for the task. Once received, sealed, and closed, the pig is driven down the line either by a cable (tethered) or by the flow of material (non-tethered). The pig then gathers important data on the presence and location of any irregularities on the inner walls of the pipe.
In scenarios where it is not feasible to conduct a hydrostatic test or in-line inspection – this could include varying pipe sizes, bends, or valves – a direct assessment is conducted. “Direct assessment involves plenty of external inspections. The first step is to complete a pre-assessment,” Araya states. “All of the previous data sheets must be reviewed to prepare a feasibility analysis, which determines whether or not it is possible to conduct a direct assessment on the pipeline.”
Cases studies of carbon, stainless steel and titanium tanks
Araya is familiar with many types of high-grade corrosion resistant alloys (CRAs) and the processes used to mitigate the risk of corrosion in each. During one project, Araya conducted an inspection at a paper mill plant, where the facility was required to upgrade a carbon steel tank to a stainless steel model. “That is not a small expense even for one valve, and all the valves at the plant and their welds needed to be changed. The mill had been replacing its carbon steel tank every three years. After careful consideration of its processes and following the behavior of the mill for eight years, it was determined that the carbon steel could withstand corrosion for up to four years, while stainless steel would resist corrosion for 10 to 12 years. By replacing the tank and its material of construction, the application’s lifespan would be increased, significantly changing the cost-benefit relation.”
In some industries, higher-grade alloys such as titanium or Hastelloy® are required for applications that need to withstand more hazardous environments. In one instance, while working in a copper mine, Araya handled the upgrade of a tank from stainless steel to titanium. “Titanium has a very high resistance to most types of corrosion in current thermodynamic and atmospheric conditions,” he explains.
Even when a high-grade material is being used, coatings for tanks should still be considered an asset. “Companies are paying for coatings, so they need to be properly checked and maintained. The lifespan of a coating must be adhered to. Often coatings are applied very well the first time and is expected to last forever, but this is not the case. It does not matter if it has been seven or 20 years since the coating was applied – you must be aware of your coating’s performance.”
Managing data and valve assets
Araya considers the data management of assets a statistical process. For example, capability analyses are used to logically estimate where corrosion will appear in the future. “In analyzing the data, you can expect the increase of corrosion rates in some areas.” Araya also breaks the data into two types: data collected and data observed.
To explain further the idea of data collection and observation, Araya detailed a project he had worked on recently. About a year ago in Chicago, Araya and his team installed a data collector in a valve. They studied the valve, put a GPS on it, and collected data for three days from the same sensor point. On days one and two, there was no inconsistent data. But on day three, the readings were considered ‘strange’. “We thought to ourselves, ‘What happened?’” The team examined the fluctuations overnight, including the impact of the rain, to see why the conditions had changed. Moisture is considered conductive and can affect readings, which is why during the dry season, these inconsistencies did not occur.