A LIFE Cycle Management/Mechanical Integrity (LCM/MI) program will provide safer conditions, risk reduction, optimization of tank maintenance and inspection costs, maximization of tank availability, regulatory compliance, and more predictable outcomes.
“It’s not that we can avoid all outcomes, but if they’re predictable and nothing catches us by surprise, that’s certainly something to go for,” said Joel Andreani, principal engineer for The Equity Engineering Group Inc. He spoke during the International Liquid Terminals Association’s 2016 International Operating Conference May 23-25 in Houston, Texas.
In his presentation, “Recommendations for Storage Tank Life Cycle Management,” Andreani said LCM is a “process of managing the entire life cycle of fixed pressurized equipment from initial design, construction, use in-service, and retirement.”
He said the goals of LCM coincide with those of MI programs: safety, reliability, environmental protection, and optimized LCM costs over the entire life cycle.
His recommendations for implementing a LCM/MI plan:
• Have a champion (MI manager/facilitator).
• Document. Early on, establish documentation requirements—suitability for service (SFS), 3D laser scans/drawings, and corrosion control documents (CCDs).
• Train. Determine training needs and consider codes and standards activities.
• Capture corporate knowledge and best practices through internal specs.
• Assess gaps and set goals for continual improvement.
• Move deliberately. It may be slow at first.
• Celebrate successes.
He said that for LCM, the applicable standard in the ASME road map is API 571 (Damage Mechanisms Affecting Fixed Equipment in the Refining Industry). From an MI standpoint, the design standards and best practices go beyond API, and written procedures may include corrosion control documents (CCDs).
In LCM, damage review involves:
• Product corrosion factors: product, temperature, biologically induced corrosion; tank design (external floating roofs versus internal, blanketed tanks, and fill frequency.
• Stress corrosion control (SCC) mechanisms (ethanol SCC and ammonia SCC).
• External corrosion (marine and contact with soil and moisture).
“All these things play into the damage review side,” he said.
In LCM design and construction, the applicable standards are: API 620 (Design and Construction of Large, Welded, Low-Pressure Storage Tanks); API 625 (Tank Systems for Refrigerated Liquefied Gas Storage); API 650 (Welded Steel Tanks for Oil Storage). Others are API 12 Series (12B, 12D, 12F, 12P), UL, AWWA, and corporate best practices.
“The Committee for Refining Equipment (CRE) has taken over the Series 12 tank documents, so we’re in the midst of a big review of API 12 Series documents and updating them,” he said. “We’re more than halfway through.”
Some best design and construction practices:
• Use annular rings.
• Ringwalls and mats. “They certainly have gone the way of preferred foundations for most things.”
• Release Prevention Barriers (with CP). “In design or retrofit situations, this is the biggest bang for the buck from at least an API 581 risk-based inspection (RBI) side of things. Mathematically, in your calculation of the consequence of a tank bottom hole, it reduces the actual product fill in that calculation from whatever the height of your tank to three inches. How they came up with three inches, I’m not sure. But that significantly impacts your RBI calculation and the required inspections as a result.”
• Specifying the sand (resistivity, pH, chlorides, and sulfates). “I’ve seen this become what may turn out to be a $40 million mistake or at least a $40 million problem. Specify things like chloride limits or the resistivity you want out of your sand.”
• API 650 Annex F and API 620 tank compression rings. “What types of compression rings out of those two books are you going to allow? There are eight or 10 or 12 varieties you can come up with, and some of them function better than others. Pick any that have both reinforcement in the shell and the first ligament, if you will, of the roof, and you will be better off than having it one place or the other.”
• Settlement measurement benchmarks. “I saw a lot of settlement measurements taken in the past than with current technology. But they’re taken all over the place and are not consistent benchmarks.”
• 3D Laser Scan (3DLS): time of construction condition, calibration of tank volume. “We’re seeing a few folks do the initial scan of your structure and its shape. You can calibrate from this and see if there were any initial problems that weren’t caught in the tolerance side of things. And also it gives you a starting point if you have settlement over the years.”
Standards for in-service inspections: API 653 (Tank Inspection, Repair, Alteration, and Reconstruction); API 580/581 (Risk-Based Inspection, Risk-Based Inspection Technology). Others are API 575, EEMUA, STI SP001. From an MI standpoint, inspection interval and process are the key.
Prescriptive versus RBI intervals:
• API 653—Prescriptive Intervals (Internal). Initial 10-year base. Extension for safeguards like lining, release prevention barriers with cathodic protection. Subsequent prescriptive based on remaining corrosion allowance. “So after I’ve done my first inspection and I have a corrosion rate calculated, I can do a prescriptive interval based on the remaining corrosion allowance.”
• API 653—Risk Based Inspection. Now you can use this for initial interval and subsequent interval. There are viscous, non-hazardous exemptions. API 580 is required by API 653. “When you use RBI to meet 653, the requirement is for the RBI to be API 580. This is the overarching general background document for RBI. It doesn’t get into calculations and so forth, but gives you a process for building an RBI team and stepping through the RBI process and documenting it along the way.”
• From an MI standpoint, RBI can be used to schedule or defer inspections. “Deferrals should be evaluated and documented. When you do deferrals of anything, but particularly inspections, there should be an evaluation step done, whether it’s RBI or not, and it should be well documented.”
Best Practices for tank RBI:
• Selecting an approach. The benefits of a quantitative approach rather than qualitative approach are consistency and repeatability.
• Inspection guidance. API 581 Effectiveness Tables are a great resource.
• RBI and tank design. Added bottom CA, annular. RPB (and cathodic protection): COF cut back by two orders magnitude. Sand can be two to three times improvement in the damage rate. Drainage, water draw, etc are all to the improvement of the RBI results.
In terms of damage and fitness for service, the standards are API 579-1/ASME FFS-1 (Fitness-For-Service); API 653 (Suitability-for-Service, Settlement FFS). API 653 directly (and indirectly) references API 579.
For FFS of tanks, five or six methods in API 579 apply to storage tanks:
• Part 3: Brittle Fracture—when you fail API 653 Section 5 method. “There are a variety of things: How thick am I? What’s my highest stress? What’s my temperature? If you fail those, there is a method in 579 that may be of value to you to define your NDMT or your DMT or whatever you are using for minimum metal temperature.”
• Part 4: General Metal Loss—when thinning exceeds API 653 Section 4.
• Part 5: Local Metal Loss—often Level 3 (bottom corner).
• Part 6: Pitting.
• Part 8: Shell and Weld Distortions/Misalignments, Settlement & Upsets (pressure or temperature)—often Level 3.
• Part 9: Crack-like Flaw Assessments—original weld flaws and actual cracking (environmental or cyclic).
Reactive uses of fitness for service (traditional use) involve finding damage “outside acceptable limits.”
“I have an equipment deficiency and I need to either repair it or check it out with a fitness for service analysis,” he said.
Proactive uses of FFS involve undocumented tanks (suitability for service assessment), brittle fracture screening/change in service—triggered by HAZOP or PSM MI, and flaw assessment criteria (hydrostatic test exemption). ♦
