Inspection and maintenance of pressure vessels are of utmost importance to conducting a safe and effective mechanical integrity program. At a typical plant, you are likely to bump into fixed assets that are clearly pressure vessels, like a butane sphere or a propane bullet tank, but equipment such as heater exchangers and condensers can also qualify as a pressure vessel under API 510.
DISCLAIMER: This article should not be construed as professional advice. While there is no substitute for an expert, certified understanding of API 510 and its reference documents, we’ve assembled a high-level list of considerations as an entry point to this topic. Gecko Robotics has on-staff API inspectors should you require consultation.
What is API 510 and What Vessels Does it Cover?
API 510 is a code written by the American Petroleum Institute to recommend best practices for the “In-service Inspection, Rating, Repair, and Alteration” of pressure vessels. This lays out the inspection intervals, items that need to be monitored and tested, calculations of critical factors, and methods of repair. API 510 also references supporting codes, most importantly API 571 and API 572, which cover Damage Mechanisms and Inspection Procedures, respectively.
The first and simplest definition of coverage is any pressure vessel that was constructed as a pressure vessel. That may seem obvious, but it is the first qualification for coverage. The ASME Boiler and Pressure Vessel Code, Section VIII is an example of this. Equipment falling under this code is typically operating at pressures greater than 15 psi. The second definition is if your jurisdiction tells you it falls under API 510. The last definition is any vessel that was constructed without a code or was constructed with a code but has lost its nameplate or stamping. This last case is a catchall to take an abundance of caution.
When Do I Need to Conduct an Inspection?
At installation: The first time the pressure vessel is inspected is upon installation. The two primary reasons are:
- to ensure that the vessel is ready for its intended operation and
- to initiate measurement baselines and record keeping.
Upon each subsequent inspection due date: Each vessel is inspected according to an inspection plan designed by the owner of the vessel. The plan takes into consideration:
- the materials the vessel contains
- type of deployment
- likely damage mechanisms
This establishes the protocols and inspection intervals for the equipment; and may follow either a fixed time schedule or an RBI program designed for the facility. At the appointed time, an API inspector conducts the inspection and communicates the findings back to the owner.
NOTE: if the type of service the vessel performs changes, a new inspection plan must be created and inspection intervals re-visited. This is good practice and stands to reason.
Change of owner and location: The inspection plan is the responsibility of the owner based on the environment. If both the owner and location have changed, API 510 requires an external and internal inspection to ensure the vessel is ready for use. If the new service is anticipated to have cracking damage mechanisms, additional baseline examinations of welds are warranted.
What are the Time Intervals Between Inspections?
There are two general methodologies for determining the interval between different types of inspections. The first method is time-based inspections and the second is risk-based inspections (RBI).
API 510 calls out four specific types of inspections:
- Internal
- External
- On-stream
- Thickness measurement
Time-based and RBI can be used to generate the intervals. For time-based inspections, those intervals are summarized below.
RBI assessments are governed by a separate code, API 580, and are unique to each owner and facility. The time intervals are governed by a facility-wide minimization of risk defined through a combination of the probability of failure and consequence of failure decisions for each piece of equipment. The intervals established by the RBI may exceed the time-based limits, with some caveats. For instance, for any RBI interval of an internal or on-stream inspection that exceeds 10 years, the RBI assessment must be reviewed at intervals not to exceed 10 years to re-determine applicability.
Are There Advantages of Similar Service Pressure Vessels?
Having a good understanding of the equipment in-same or in-similar service has the potential advantage of being able to substitute an on-stream inspection for a 10-year internal inspection. The benefits of replacing an internal inspection with an on-stream are numerous. First and foremost, the vessel can be kept online doing its job saving costs associated with emptying the contents and cleaning it to prepare for a confined-space-entry (CSE). Because there is no CSE required, the owner avoids a hazardous entry, thus increasing safety, not to mention costs due to additional personnel monitoring the CSE.
This technique is most suitable when you have a large number of pressure vessels in similar service and you have a strong grasp of the corrosion environment. According to API 510, this is only permissible when there are more than 10 years of service life remaining. In addition, there are a number of other requirements that must be true to take advantage of this comparison.
What Should Be Done After an Inspection?
The inspection is the start of a set of in-concert activities for that inspection interval. Based on the inspection and its recommendations, the owner will need to update the calculations for the vessel, make immediate (reactive) repairs, and plan for additional predictive maintenance to coincide with an upcoming turnaround.
Assuming all the required maintenance is completed or scheduled, and the vessel is in a stable condition, the focus of the post-inspection steps can focus on making the best decision on the next inspection interval. That will be determined by the calculations of short-term and long-term corrosion rates, Maximum Allowable Working Pressure (MAWP), and remaining life estimates. In addition, Fitness-For-Service (FFS) estimations need to be applied to key structural areas and any evidence of corrosion or damage.
The last step is to fully document these findings into the inspection plan and/or RBI assessments for that pressure vessel.
Summing it All Up
Every piece of equipment has its own personality and nature. Luckily, the API codes have been written to steer owners and maintenance professionals towards best practices to maximize safety and effectiveness across classes of assets. In this blog, we covered key considerations covered under API 510 for pressure vessels. Our goal is to highlight aspects of the code for the owner/operator for further investigation.
Gecko Robotics has an on-staff team of API inspectors that can consult on any and all aspects of the API 510 Inspection process. Head over to our API 510 Pressure Vessel Inspection Program page to learn more.
