Corrosion and Wear: The Persistent Threat
Challenge
Some of the most familiar issues relating to the above-ground storage tanks include; Corrosion. External corrosion and internal corrosion usually contribute to the thinning of the metal of the tank and can also cause pitting as well as extensive structural failures. Most tanks are very old with many constructed over three decades ago, and the plate corrosion may alter the tank shell, bottom, or roof, thus posing a safety and/or environmental hazard.
Corrosion can be caused by several factors, including:
- It is equally vulnerable to moisture and oxygen in the environment.
- Direct interaction with crude natured chemicals and petroleum products has been noted to be stored in the tank.
- Some of the things include corrosion or deterioration of protection including coatings or cathodic protection.
Moreover, the normal usage of tanks to contain ‘‘bottoms’’ and ‘‘sidewalls’’ experiences considerable wear and tear arising from regular operations such as filling, emptying and product movement which can worsen the situation in terms of corrosion.
Solution
A proper strategy in handling corrosion or wear problems in tanks required repair is to adopt detection at the initial stage and repair before the problem compound. NDT is important for periodically inspecting pipes before corrosion is allowed to progress to the point where corrective action is expensive; the most common NDT are UTT and MFL.
When corrosion is identified, there are several ways to repair the damage, depending on the severity:
- Welded Repairs: When corrosion occurs at only one area, major corrosion or pitting, reinforced or renewed welds can be applied to the tank. In API 653, some information with regard to the kinds of welding practices that is desirable or acceptable and tests that should be performed after repair or welding is given.
- Bottom Plate Replacement: In severe corrosion areas, especially on the bottom of the tank, shell or tank bottom may require full or partial change. API 653 defines how bottom plates can be removed and or replaced while maintaining the stability of this equipment as well as meeting the requirements of its standards.
- Corrosion Prevention Systems: Cathodic protection systems can be installed or upgraded to provide protection to the tank in the future, as well as reapplying coatings. The survivability of these tanks depends largely on proper maintenance of the underlying systems on a continuous basis.
Settlement and Foundation Issues
Challenge
From the case of large liquid storage tanks, it is possible to have a ground load pressure which causes a settlement of the tank foundation. API Spec 650 states that uneven settlement is very bad for the tanks since it brings about deformations on the shell and at the bottom of the tank and may lead to leakage, cracking and overall failure of the tank.
Leakage could also be another cause of foundation problems because generally, water is likely to accumulate under tanks, which in turn leads to the weakening and consequently the sinking of the tanks.
Solution
To avoid complications regarding settlement problems, it is obligatory to design and maintain the foundation of the tank. API 653 or tank inspection codes outline how the integrity of the foundation and evidence of settlement can be assessed through cracking, tilting and any distortions seen in any structure of the tank.
Steps to address settlement and foundation issues:
- Foundation Inspections: Basically, a construction engineer should note that the process of settlement detection should involve both visual and instrument foundation inspection of the tank. Should settlement be observed, additional investigation based on soil analysis should be carried out to establish the extent of the problem.
- Re-leveling the Tank: In the worst case, an uneven settlement might have happened and, therefore, it will be important to re-level the tank. This is done through hydraulic jacking where the tank is raised and then the foundation is realigned or strengthened in order to gain balance.
- Foundation Upgrades: Sometimes the potential tank base requires reinforcement or even complete replacement. This could be done by enhancing the subgrade around the tank by putting a better drainage system or compaction of the soil or by installing more support structures like gravel beds or concrete annular rings.
Preventing undue settlement in the first place can be accomplished by making certain that all tanks are erected on well-prepared foundations and that adequate provisions for drainage are made when constructing tanks.
Dealing with Hazardous Materials
Challenge
Hazards are associated with many tanks such as containing flammable liquids, toxic chemicals or any substance that will cause corrosion. Such an endeavor further exposes workers and the environment at large more and especially when the tank is in use or contains residual products.
However, they must be emptied, cleaned and decontaminated before any repair work on the tank can begin safely. But this process is usually tiresomely involved and may pose some serious risks of exposure to some hazardous vapors or materials in the course of the process if certain and specific measures are not fully followed. Furthermore there is a likelihood of polluting the environment during the cleaning and repair process.
Solution
Dealing with repositioned tanks that may carry hazardous material requires that other strict safety measures be observed, and that employees working with the tanks should be trained on safety measures to observe as well as provided with PPE.
Steps for safely handling hazardous materials during tank repairs:
- Tank Cleaning and Decontamination: Any repairs to the tank require the container to be drained and then washed so as to remove any existing liquids, sludge or other hazardous substances. This may be achieved by use of pressure washing or steaming and sometimes, depending on the contents of the tank, the use of chemical washes.
- Gas-Freeing Procedures: After cleaning the tank, it is made free of gas, and this is in a bid so that there are no dangerous gases trapped inside the tank. This is undertaken in a bid to eliminate compressed flammable or even toxic gases within the tank with a view of minimizing incidents such as explosion or chemical influence on the employees.
- Environmental Protection: To avoid water pollution it is advisable to provide so called secondary containment systems or spill sensitization during the cleaning and repair work.
- Safety Plans and Permits: It is also important to ensure that all repairs are conducted under certain standard operating procedures such as acquisition and alteration of a variety of permits and compliance to confined space entry.
Welding Challenges
Challenge
Allow us consider welding as an essential step in repairing the tanks, as it comes as the main component of most techniques of repairing the tanks, where there are some corroded sections, or when there is need to replace bottom plates or even alter the structural shape of the tanks. Welding on tanks is not as straightforward as welding on flat surfaces; in fact, each tank comes with a challenge especially if it were old or previously used to store chemicals.
Key challenges include:
- Welding on thin or corroded metal where there exists high risk to produce new leaks or points of corrosion inclusion.
- Inspection and guarantee of the quality of welds that is consistent with API 653 and capability to pass through testing that is carried out after welding.
- Preventing the welds forming part of the structure from being contaminated by residues of the tank contents.
Solution
It is therefore critically important to engage skilled welders and to plan effectively if welding challenges are to be surmounted. The welding process must be controlled especially to conform to the API 653 standard and any other lug standards.
Strategies for overcoming welding challenges:
- Pre-Weld Testing: Check the tank material for any damage using Non Destructive Testing (NDT) technique to be very certain that the material used in constructing the tank will not buckle or crack under heat and stresses of welding. It can point out some of the problem areas, which may need to be strengthened in order to improve the overall result of the learning process for all the learners.
- Welding Procedures: Perform welds in accordance with the method of welding that is recommended for the type of material used or the thicken-ness of the tank. API 653 also describes the correct kind of weld to apply when repairing the tank depending on the particular situation.
- Post-Weld Testing: In order to ensure the quality of welded connections, perform the non-destructive test to check welded parts with, for example, a radiographic test or an ultrasonic test. Before the tank is put back into use any flaws or areas of constructive failure should be rectified.
Occasionally, more sophisticated methods of welding, like hot tapping, which permits the making of welds on a tank whilst in service may be necessary to reduce time loss.
Ensuring Compliance with API 653
Challenge
Tank repair works present one of the most significant concerns of the necessity to complete all such works according to API 653. The standard is rather broad and provides not only the recommendations for intervals between inspections but also for welding. Inadequate compliance with API 653 can lead to potential risks which include the following; safety risks, regulatory consequences, and higher liability costs on those operating the facilities.
Solution
It is therefore important to state that the need for compliance to API 653 involves a good plan, documentation, and expertise. This means that only certified inspectors and contractors who are conversant with the standard should be used in carrying out the repairs with a view of ascertaining that all works meet the necessary requirements.
Best practices for ensuring API 653 compliance:
- Use Certified Inspectors: Tank inspections and repair should only be done by certified API 653 inspectors. These inspectors are fully conversant with the details of this standard and can guarantee that all work to be done is done to the required specification.
- Maintain Detailed Records: It is important to maintain the records of all sorts of inspections, repairs and alterations done on the building. This entails documentation on the type of NDT done for the tank, the welding process and any alterations of the tanks structure.
- Regular Audits and Reviews: All tanks requirements be submitted to regular audits to enable the implementation of the tank maintenance program to meet the set API 653. It could assist in helping avoid problems once they get major and make sure all the repairs have been made on time.
Conclusion
Redevelopment aboveground storage tanks as per API 653 is a very time consuming and technical job which involves proper planning, skilled work and quick execution along with safety norms and compliance with government rules and regulation. From economical considerations such as controlling corrosion and settlement to specialized issues such as handling of hazardous products or poor weld performance, each is best addressed by a unique approach.
These issues and their solutions show that when facility operators and their repair teams are aware of them, their tanks can continue to be safe, reliable and in contravention of the API 653 standard. Finally, this assists in avoiding accidents, decreasing downtime, and increasing the operational time of the important storage systems.