Question 70: How frequently do you have fires on reformer reactor flanges? What bolting techniques and gasket types do you use to prevent leaks? What other fixes, such as flange resurfacing, have you employed? Do you use steam ri
GRUBB (Chevron USA, Inc.) Chevron has had some experience with flange fires in the past, so I’ve consulted with Dave Reeves, our corporate expert and also our Best Practice that we’ve developed for this. I know that I said temporary fixes up on the slide, but it’s not really a temporary fix. It’s more like you discover you have a leak and decide to temporarily put this on. It’s more like temporary while you’re figuring out the solution for the right gaskets to use. So we’ve employed some steam rings around some of these that were prone to leaks. Some of the leaks, since they’re hydrogen fires, are not visible during the day, so we’ve employed wrapping chicken wire around some of the rings to show the burn when it happens. The Best Practice that we developed and came up with was Kamm profile gaskets for anything over 24 inches. Some of the details are that the flange surface should be finished to 125 rms to 250 rms; you should use a high quality graphite material for the gasket covering; and, the stud loads should be set to between 20,000 psi and 25,000 psi gasket stress. We use a modified star pattern for bolting where we do the first four nuts in the star pattern, and then we go clockwise around twice, torquing to 100%. One keynote where we may have had problems since we’ve come up with these, our gasket selection has been fairly successful. Where we’ve had problems in the past is where we discovered a flange was accidentally insulated over, and then the bolt stud doesn’t hold under higher temperatures. We now try to go make sure that our flanges are not insulated after we’ve done maintenance.
NEWTON (Roddey Engineering Services, Inc.) Most of the refineries we work at use a two-step torquing procedure. They either get a hydraulic torque wrench or, as our Mechanical Engineer says, they take the end of the bolt and stretch it to 65% to 70% of yield strength and then hand-tighten the nuts. Then, you start heating up. After you reach a specified temperature, just go ahead and tighten it up all the way. One issue that he discussed with me about when we do the hydraulic torquing is to make sure that the service area is clean. You don’t want to have anything that would give you false readings. Most of the places we’ve worked in have had outside contractors come in and do this and that could be recommended.
Another solution we’ve seen is to use the Bellville type washers. I did not get permission from them to use any kind of diagram, but you can go to their website and see what they look like. But basically, it’s a spring-type washer to help the metal contacts or expands. It adjusts for that. Every client we’ve had use that has had great success with these washers.
HAZLE (NPRA) Relative to the two-step bolting procedure, Shell Deer Park recently had a flange fire on one of their reformers. They have a two-step procedure like that. They missed one of the flanges when they were going around and re-torquing and had a small fire, which then interrupted their startup. So to me, that’s an endorsement of that particular feature.
BRIAN HARRIS (Holly Refining & Marketing Company - Woods Cross) I am wondering if most people find that we have more failures. And if you cycle more, do you have to go back and retorque? Let’s say, you had a crash-down or a shutdown and you cooled off, do you go back and retorque at that point or are you good once you hot-torque the first time?
GRUBB (Chevron USA, Inc.) I don’t believe you go back and retorque.
NEWTON (Roddey Engineering Services, Inc.) We don’t retorque either.
MIKE FACKER (Western Refining Company) I just want to mention that as far as finding the leaks, we use a clear camera where you can see a lot of your vapors. It looks like a steam leak coming out of there, and that’s been handy detecting some of the leaks when you’re starting out.
Question 71 Is your company planning to install modified HF acid capability (usage of the volatility suppressing additive)? What are the incentives for doing this? What alternatives have you considered?
METKA (Sunoco, Inc.) In March 2006, in our continuing effort to support safe, reliable, and environmentally sound operation, we announced our plans to apply for a permit to independently initiate an alkylation process improvement project in our Philadelphia HF alkylation unit. The unit employs ConocoPhillips, now UOP, Split Olefin Feed Technology (SOFTTM), and the project includes voluntary incorporation of a modified acid capability. ConocoPhillips ReVAP® technology was selected for the project. As most of you are probably aware, this technology was later acquired by UOP. We had been evaluating the incorporation of modified acid technology for several years in order to determine if the technology could be applied without contributing to reliability or other operational concerns. Other options were considered and ReVAP® was selected based on demonstrated commercial application. The additive used in the modified acid technology reduces acid volatility, which provides several benefits. It provides a passive mitigation system that further enhances existing safety measures. Transportation risks are also reduced since the additive can be blended prior to shipment. Modified acid technology is one ingredient of an extensive safety program and it compliments other acid management systems, which include extensive inspection, maintenance, and equipment monitoring programs, existing active mitigation systems, feed quality control through selective hydrogenation, an online HF analyzer for continuous acid monitoring and control, and a rapid acid de-inventory system. The technology also compliments the planned implementation of compartment technology, which is another passive system, including a baffle in the settler that reduces the amount of material available in the unlikely event of a release. Other potential benefits include decreased acid usage and also slightly higher alkylate octane.
QUINTANA (Valero Energy Corporation) This response focuses more on the latter part of the question related to alternatives, which John has already touched on with a good start. We see vapor suppression additives as only one option of several available for consideration as part of a comprehensive Process Safety Management (PSM) program. The industry recommendations to consider are summarized in API Recommended Practice 751 for Safe Operation of HF Acid Alkylation Units. We believe an effective program will comprise of recommendations emphasizing leak prevention and monitoring, as well as the mitigation systems to be used in case of a leak event.
There are various elements recommended under RP 751 that are included in The Answer Book and the next three slides, so I will not go over them in detail here. The key elements include procedural aspects such as HAZOP assessments, MOC (Management of Change) programs, emergency response and control plans, and regular unit audits.
API RP 751 Elements:
•HAZOP assessment of existing unit equipment & controls
–per API RP 750 - Management of Process Hazards
•Management of Change program to address controls, instrumentation, metallurgy, procedures, relief system
•Thorough emergency response and control plan
Regular and thorough unit audits to address:
- Unit specific & industry incidents and risk exposure in the unit
- Inspection, maintenance & training records
- Mechanical & procedural changes since previous audit
- Testing & maintenance of detection, monitoring, control systems
- Testing & maintenance of mitigation systems in case of a leak
- Procedure compliance, understanding via observation, interviews
- Technology developments that further reduce accident risk
There are also equipment aspects, including regular equipment inspections, confirmation of correct metallurgy viamositive material inspection (PMI) programs, use of reliable instrumentation and minimum acid inventory, and then the mitigation systems.
API RP 751 Elements:
•A comprehensive program should include (continued):
–Regular and rigorous equipment inspections to confirm integrity of unit equipment, especially acid containing equipment
–Use of correct metallurgy
- per NACE 5A171
•Confirmation with Positive Material Identification program, especially in case of repairs or changes to equipment, piping
–Tracking mechanism to ensure resolution, close‐out of identified issues
–design tracking system to facilitate next audit
–Reliable level instrumentation systems less prone to fouling, such as nuclear, radar, ultrasonic or magnetic
–Minimum acid inventory
–Mitigation systems
These mitigation systems can include a variety of active and/or passive elements along with tell-tale components. The main active mitigation system components include water deluge or curtain systems, remote monitoring and activation systems, and rapid dump systems to limit the quantity of any leak and contain the leak to the unit area. Vapor suppression additives fall under the passive mitigation category and can be considered along with all of the other possible elements available as part of a PSM program.
API RP 751 Elements:
Mitigation systems can include active and/or passive elements as well as tell‐tale components:
- HF detectors can be point, open path or imaging systems
- Install as needed in unit risk envelope
- Acid sensitive paint on flanges, pump seals, etc.
Active mitigation systems can include:
- Water deluge and/or water curtain systems
- Remote video monitoring and remote activation, isolation systems
- Rapid dump system to contain acid, limit the extent of the leak
Passive systems can include:
- Barriers & catch pans to contain acid release
- Minimum acid inventory control & staging in equipment
- Vapor suppression additives
Each facility should assess its own location-specific risk profile and develop a mitigation strategy that includes the elements that together effectively minimize those risks while conforming to the applicable regulations for that facility.
API RP 751
Conclusion:
- Each facility should determine their location
- specific risk factors, and assess the appropriate combination of active and/or passive mitigation systems needed to minimize risks involved in operating the unit
- Local, state and/or federal laws and regulations should also be reviewed