When an ASME Code Stamped Pressure Vessel is built, it is fabricated to the specifications of the ASME Boiler and Pressure Vessel Code. Repairs, however, are covered by the National Board Inspection Code, commonly referred to as the NBIC.
Common Pressure Vessel Repairs
Some of the most common types of repairs to pressure vessels that are covered by the NBIC include:
Failed and corroded weld repairs
Nozzle replacement and installation
Heat exchanger tube repair or replacement
Mounting clips for ladders and other externally mounted components
1. Weld Repairs
Anywhere there’s a joint, there’s a potential weakness in your pressure vessel. Especially in pressure differentials, welds can fail under stress. There are many causes of weld failure, some occurring in production, such as porosity in the weld or the inclusion of slag. Others — namely corrosion — occur over long stretches of time, as the weld is exposed to the elements and gradually corrodes, eventually causing cracks and other issues.
2. Nozzle Replacement and Installation
Nozzles on pressure vessels see a lot of use, and as such, they comprise a common type of pressure vessel repair. Nozzles can wear out over time, and their components can become degraded, sparking a need for replacement. Additionally, installing new nozzles when the need arises is common and also falls under the NBIC. Technology can change over the lifespan of a pressure vessel (which can be over 20 years), and replacing older nozzle designs with new, more efficient ones can be a repair well worth making.
3. Heat Exchanger Tube Repair or Replacement
Graphite heat exchangers on pressure vessels can require a variety of tube repair services, as tubes and tube sheets can take a variety of damage: corrosion of the tube or sheet end, cracking, joint failure, excessive loads, and vibration damage or weakening of the tube materials. When these kinds of issues occur, tubes and tube sheets can be totally replaced or repaired by means such as plugging the damaged tubes or with welding or adhesives.
4. Mounting Clips for Ladders
Working on and around pressure vessels carries some inherent risk. For cases when ladders must be installed on pressure vessels for access to gauges or making repairs, mounting clips are to be installed according to the code, in order to prevent damage to the vessel itself and ensure adequate, ergonomic access to necessary components of the equipment for technicians.
Any repairs or additions that require welding non-pressurized components to pressurized components or boundary components of the vessel fall under the NBIC, and require special care to guarantee the soundness of the weld and avoid compromising the vessel’s ability to maintain the pressurized environment.
Inspecting for Necessary Repairs
Because pressure vessels are pressurized and contain sensitive materials, keeping up with maintenance and repairs is critical. To know when repairs are needed, reduce downtime, and keep your pressure vessel operational, you should have a regular inspection program.
The NBIC clearly defines who is and who is not authorized to conduct repairs that fall under the code, like fortifying corroded welds. To perform repairs governed by the code, repair shops must be certified by the National Board to use the proprietary R-stamp. This certification ensures the qualification of the servicer to meet the necessary design, materials, and quality standards of the code.
When you need NBIC-compliant pressure vessel repairs, call PALA. We are certified to use the NBIC R-stamp, and can perform all repairs governed by Part 3, Section 3 of the National Board Inspection Code. We fabricate and service a variety of pressure vessels, including ASME Div. 1 and 2 code vessels, API 650 and API 620 tanks, and Section VIII pressure parts. We not only hold the NBIC R-stamp accreditation, but also accreditation for U-, U2-, and S-stamps.
Industrial pressure vessels provide the safe storage of a variety of materials, some relatively harmless and others volatile or hazardous. Regular inspection and testing are a must whether it be for a storage tank or vessel, a boiler, a heat exchange, a process vessel, or some other type of pressure vessel. Because of the extreme pressure in most vessels, it’s essential that they are always in top shape with no leaks, cracks, or deficiencies.
In this article, we’ll cover the general pressure vessel inspection and testing requirements, as well as what a pressure vessel inspector is looking for during an inspection.
How Often Should Pressure Vessels Be Inspected?
As a general rule, any pressure vessel should be inspected once it is installed and before it’s put to use. This ensures that any pressure vessel going into service is tested and approved to perform as it should.
Outside of starting service, pressure vessels should be inspected and tested at least every five years. Specific requirements vary by industry and by hazard potential of the vessel. For example, a vessel containing more hazardous materials will require more frequent inspection than a vessel with relatively safe contents.
Some common pressure vessel standards include the ASME Boiler and Pressure Code, the AIAA Metallic Pressure Vessel Standard, and the API 510 standard. The specific standard your vessel must adhere to will again depend on your pressure vessel, its contents, your industry, as well as your location.
5 Types of Pressure Vessel Testing
There are a variety of ways a pressure vessel can be tested, depending on what an inspector is looking for, the contents of the pressure vessel, and what kind of inspection is required. For example, an NDT (non-destructive testing) method is necessary if a pressure vessel is in use. An internal inspection may be required for more in-depth inspections, which must happen while the vessel is empty. Some of the most common types of pressure vessel testing include:
01. Visual Testing
Visual testing is the most common form of pressure vessel inspection. It’s non-destructive and mostly consists of an inspector looking at the vessel’s interior and exterior for any cracks or flaws in the vessel.
02. Dye Penetrant Testing
This is a unique type of testing where a liquid containing a fluorescent dye is sprayed onto a pressure vessel. When put under a UV light, the dye will glow, identifying any defects or flaws on the pressure vessel’s surface.
03. Ultrasonic Testing
Ultrasonic testing is used to detect any possible flaws both on the surface of and within a pressure vessel. Using sound waves, an inspector can measure the thickness of a material’s surface, telling them whether there are any interior or exterior defects.
04. Magnetic Particle Testing
Used to test the surface of a pressure vessel, in magnetic particle testing, a magnetic current is sent through the vessel to identify any deformations or surface defects.
05. Radiographic Testing
Another volumetric form of testing, radiography is used to detect defects near or on the surface of a pressure vessel.
Pressure Vessel Inspection Checklist
With a clearer picture of how pressure vessels are tested, you may wonder what a pressure vessel inspector is looking for during that testing. While this is by no means a comprehensive list, here are a few key items inspectors watch out for during both internal and external inspections.
Internal Pressure Vessel Inspection
Internal inspections are performed when a vessel is empty or not in operation. They require close attention to detail on the inside of the vessel. A few key items an inspector is looking for include:
Any possible defects. Anything from a small crack to a bit of corrosion, blistering, or even a more significant deformation can all point to a defective pressure vessel in need of repair.
Secure threaded connections. An inspector will inspect all threaded connections to ensure that the right number of threads are engaged to properly secure connection points.
Any openings. If the pressure vessel has any openings, like external fittings or controls, the inspector will check to ensure there are no obstructions to those openings.
Special closures. Any special closures will be inspected to ensure they are closing properly and securely.
High-stress areas. Pressure vessels are designed to store contents at high pressure. Any pressure vessel has high-stress points and areas that are more prone to wear. An internal inspection will closely examine these areas to ensure the pressure vessel is in good shape.
External Pressure Vessel Inspection
External inspections can be completed when a vessel is in operation or when it is empty. These are usually more frequent than internal inspections as they can be completed at any time. External inspection points usually include:
All coverings. Any pressure vessel covering, including any insulation or corrosion-resistant coatings are inspected for defects. Missing coating or insulation can lead to bigger problems down the road, so it’s important to identify and fix them sooner rather than later.
Exterior of the pressure vessel. The entire exterior of the vessel is inspected for any signs of leakage. Whether a vessel contains gas, vapor, or liquid, an inspector will look closely to ensure there are no escape points for any contents.
Mountings. All mountings will be inspected to ensure they are allowing for the proper amount of expansion and contraction.
Vessel and vessel connections. All connections will be inspected to ensure there are no cuts, cracks, gouges, or deformations. The inspector should extend this part of the inspection to nozzles, manholes, and reinforcing plates.
Nuts, bolts, and flange faces. Any additional components on the surface of the vessel will be inspected for defects and corrosion.
Shell surfaces and heads. All shell surfaces and heads will be inspected for deformations like blisters or bulges.
Welded joints and adjacent areas. Welded joints are a notorious weak point for any pressure vessel, which is why special attention will be paid to welded joints and surrounding areas.
Pressure vessel inspection is necessary for the safety of your facility and its employees, as well as for the profitability of your organization. Poorly maintained pressure vessels are both dangerous and expensive. No matter which type of pressure vessel your facility has PALA can ensure it’s always in peak operating condition.
The experts at PALA are specialists in pressure vessel design, fabrication, and maintenance, so we’re here to support you from start to finish. Holding R, U, U2, and S stamps, we’re qualified to deliver the best in service, time and time again. For more information, give us a call or contact our team.
When it comes to pressure vessel fabrication, you need manufacturers who are certified experts. They must be capable of completing your projects to the required standards. With that in mind, it’s important to know what the required standards are for pressure vessels, and how they’re indicated. This blog will cover U, U2, R, and S stamps, what they are, and why they’re important.
What are pressure vessel stamps?
Pressure vessel stamps are certifications awarded to manufacturers and inspectors of pressure vessels for compliance with specific pressure vessel code requirements. Vessels that are designed, constructed, inspected, and tested by manufacturers that have been awarded a stamp for their compliance with the specific code bear that stamp.
Essentially, a pressure vessel stamp is a certification or guarantee of quality. This is similar to other industries, where you may see a stamp or sticker on an item verifying that it has been inspected by the quality assurance team and meets the relevant specifications.
Where these stamps differ from other QA/QC stamps is that they aren’t internal to the manufacturer—they’re determined by a third party against standards that are not developed by the manufacturer, but by a third party. This means that there is consistency in the minimum acceptable quality of stamped vessels across manufacturers.
What do the different pressure vessel stamps mean?
Pressure vessels bearing the U stamp meet the requirements of a pressure vessel described in Section VIII Division 1 of the BPVC.
In order to retain the use of the stamp, manufacturers must update design and fabrication processes regularly and are subject to routine inspections and examinations.
The U2 stamp is also an ASME certification for pressure vessel design, fabrication, inspection, and testing. Pressure vessels bearing this stamp meet the requirements for pressure vessels described in Section VIII Division 2 of the BPVC. This division of the standard provides rules alternative to those of the U stamp.
The ASME stamp allows manufacturers to fabricate ASME-compliant pressure retaining parts, power boilers, and power piping. Like the U and U2 stamps, it requires a quality assurance program that meets the standards outlined in the ASME Boiler and Pressure Vessel Code.
Retain a complete copy (print or electronic) of the current edition of the NBIC.
Retain and make accessible a copy of the construction code relevant to the scope of work.
Have an inspection agreement with an inspection agency that is authorized by the NBBI.
Complete the application process for the R stamp Certificate of Authorization.
Why are pressure vessel stamps important?
If your industrial application uses pressure vessels of any kind, pressure vessel stamps are an important consideration when choosing a manufacturer from which to source your pressure vessels. The stamp assures that the vessel will meet the requirements of the relevant code, ensuring that the vessel will be fit for service in your application.
Additionally, codes like the ASME BPVC exist to ensure safe and efficient operations of pressure vessels. Depending on your application and industry, regulations may require that your pressure vessels meet the requirements of one of these stamps. Such regulations may also stipulate inspection criteria and timelines, including requiring certified inspectors.
No matter which stamp you need or which ASME code requirements your pressure vessel must meet, the PALA team has the facilities and the capability to deliver. For more information, give our team a call or contact us online today.
Pressure vessels are storage tanks that are designed to maintain a pressurized environment. These vessels are used in many industries and applications to contain things like hazardous waste, petrochemicals, flammable liquids, and much more.
The nature of pressure vessels and the requirements for these containment systems make the material used for pressure vessel fabrication of the utmost importance for maintaining compliance and optimal function of the vessel, given its specific application. While pressure vessels are made of many different materials—including chrome, steel, aluminum, nickel, fiberglass, and even plastic—here is the run-down on four of the best materials for pressure vessels: titanium, nickel alloys, stainless steel, and carbon steel.
Titanium Pressure Vessels
Titanium has several unique benefits that suit it to use for pressure vessel construction. Not only is titanium resistant to corrosion and easy to clean and maintain, but it is also non-toxic in its natural form—meaning that titanium is biocompatible (compatible with and not harmful to living tissues), a crucial characteristic for many industries’ applications. Titanium is strong and durable, maintaining its structural integrity, with tensile strength ranging from 30,000 psi to 200,000 psi (210-1380 MPa). It also has a higher melting point than steel and many other materials.
Titanium Pressure Vessel Applications
Titanium-fabricated pressure vessels are frequently used in sectors such as:
Oil and gas
Nickel Alloy Pressure Vessels
Nickel Alloy Benefits
Pressure vessels fabricated from nickel alloys have long lifespans due to the performance characteristics of such alloys. They resist corrosion and have ideal oxidation and carburization levels, allowing for use in harsh, inhospitable environments. Nickel alloys offer protection from thermal expansion to both the contents of the vessel and the vessel itself.
There are many different nickel alloys to choose from, depending on the specific application and desired performance characteristics. Alloys known for their high performance include Monel, Hastelloy, Inconel, Alloy 20, and Haynes Alloys, among others.
Nickel Alloy Pressure Vessel Applications
Pressure vessels fabricated from nickel alloys have myriad uses across industries such as:
Stainless Steel Pressure Vessels
Stainless Steel Benefits
Stainless steel is beneficial as a material for pressure vessel fabrication because of its performance characteristics and versatility. Stainless steel is durable and can withstand both very high and low temperatures, as well as high pressures, direct sunlight, and humidity. It resists rust, stains, and a wide array of chemicals, which enhances its lifespan and allows it to be easily cleaned for use in applications requiring a high level of purity.
Stainless Steel Pressure Vessel Applications
Given its versatility and durability, stainless steel pressure vessels have numerous use cases across many industries. Some notable applications include:
Food and beverage
Carbon Steel Pressure Vessels
Carbon Steel Benefits
Carbon steel is frequently used as a material for pressure vessels, and for good reason. It is resistant to melting, cracking, and other forms of damage. Carbon steel resists shock and vibrations and has high tensile strength. Like stainless steel, carbon steel is durable and able to withstand high pressures, generally at a lower price point than stainless. Carbon steel can corrode, but vessels made of carbon steel can be galvanized or coated to protect them from rust. An additional, underrated benefit of carbon steel is that it can be easily recycled, which is an increasingly important consideration in nearly every industry and use case.
Carbon Steel Pressure Vessel Applications
Carbon steel pressure vessels are used in a variety of industries, and are commonly seen in:
Oil and gas
Paper and pulp
The performance attributes of these materials make them ideal for pressure vessels in diverse contexts and use cases. Titanium, nickel alloys, stainless steel, and carbon steel all boast durability and resistance to leaks and cracks, which is absolutely necessary for maintaining a pressurized environment, especially for containment of sensitive materials. In addition, these materials used for pressure vessels boast many other qualities that suit them to industrial applications.
Whether your application requires stainless steel, titanium, or any other pressure vessel fabrication material, PALA is here to help. Our fabrication facilities in Baton Rouge and Hammond, Louisiana are equipped to handle pressure vessel fabrication and maintenance with ease. Part of our 70,000 square foot facility includes 10,000 square feet of a designated alloy shop so we can provide you with an exceptional product regardless of the complexities involved. Some of our qualifications and capabilities include:
U, U2, R & S Stamps
Section VIII Pressure Parts
Design and fabrication of ASME Div. 1 and Div. 2 Vessels (Design using PVElite Eng. Software)
A pressure vessel is an extremely important piece of equipment that enables the proper function of a variety of machines in countless industries, including food, chemical, petrochemical, pharmaceutical, oil and gas, and many more. Designed as a storage tank that holds gasses or liquids at a much higher or lower pressure than the surrounding environment, a pressure vessel provides a safe place to contain substances that are crucial to the manufacture of various products.
Importantly, not all pressure vessels are designed the same way. Many different types exist based on their function and the substances they will contain. And because a leaking pressure vessel poses a serious threat to its surrounding environment, experts take great care in the design, construction, and testing of a pressure vessel before it’s put to use.
Working with a trained expert who has a keen understanding of the different types of pressure vessels as well as the corresponding inspection codes will help ensure proper function and safety. It’s also helpful to familiarize yourself with the basic types of pressure vessels, how they are categorized, and how they are used.
Types of Pressure Vessels by Shape
Pressure vessels are often categorized according to their shape, which helps determine how they are made and what they are for.
Cylindrical Pressure Vessels
As the name suggests, a cylindrical pressure vessel has a cylinder-shaped shell with an enclosure on each end. These are the most common pressure vessels because they are easy to produce, inexpensive, and versatile. Though they have weak spots on each end where the head connects to the shell, this weakness can be mitigated by using a thicker material and more rounded end enclosures.
Spherical Pressure Vessels
In contrast to the cylinder, the spherical pressure vessel doesn’t have the same weak spots since the internal and external pressure is evenly dispersed across the entire surface. On the other hand, the spherical design is much more difficult and expensive to produce.
Types of Pressure Vessels by Function
Another helpful way to distinguish the most common types of pressure vessels is according to their primary function.
A storage vessel is a holding container for liquids and gasses typically used for industrial purposes. These substances might include natural gas, liquid nitrogen, petroleum products, or even air or water at high or low pressures. It may hold substances until they are needed in the production process, or it may hold the finished product prior to packaging and distribution. These storage vessels provide a protective barrier for both the product itself and the outside environment.
Heat exchangers shift heat from one liquid to another and therefore experience pressure due to the temperature differences. In some instances, it’s necessary to remove the heat because it is a detriment to the production process. At other times, a heat exchanger is used to add heat to a chemical process. These are used in nearly every type of industry, including food, energy, bioprocessing, manufacturing, and pharmaceutical.
Process vessels hold liquid and gas substances during important parts of the production process. The substances within are combined in some way to create a new product, and this reaction can create significant internal pressure changes. Process vessels vary in design depending on the process they are being used for, which may include mixing and agitation, decantation, distillation, and chemical reaction.
Whatever the situation may be, it’s crucial to have the right type of pressure vessel constructed by trained experts with a keen understanding of industry regulations and safety standards. From storage vessels to process vessels, we are your industrial construction and fabrication experts. With fabrication shops in Hammond and Baton Rouge, Louisiana, we are equipped to design, fabricate, and repair pressure vessels for your application. Contact the PALA team today to get started!