Month: June 2021

Your pressure rated vessel needs to be repaired to the required standards to ensure safe operation.  But, how can you be sure your vessel meets those standards when the repair is complete?  Ensuring an ASME Code Weld repair is completed in accordance with ASME Division I Section VIII Rules for Construction of Pressure Vessels requires several steps.

Let’s dig into the process. 

When you have a pressure rated vessel that requires modification – or in need of repair that includes welding – gathering the right information is the most important factor in getting the project moving correctly.

First, get the build drawings and the vessel’s U-1 Report. These essential elements include the necessary calculations that ensure its pressure rating won’t be compromised by the modification or repair.

Once an engineer completes any follow-up calculations, any replacement parts must also be tested prior to installation, in order to ensure the replacement parts are also up to standard.  Be sure that your replacement parts include a material test report (MTR) and that these reports are reviewed prior to installation.

Next, remove the broken unit or make the necessary modifications.  Once any replacement components have been welded into their required locations, polish the surface surrounding the repair to the finish specified in the original drawings.

If the equipment requires electropolish and passivation, a qualified surfacing finishing technician ensures both processes meet the required standard to complete the repairs and prepare the vessel for testing.

Finally, once the repairs, modifications and polishing are complete, test the equipment per the specifications from the U-1 Report. This test must be witnessed by an Authorized Inspector in order to meet ASME specifications.

Once the vessel passes all tests, the repair tag will be welded to the vessel and it is ready to be placed back into service.

Your choice in service providers is critical to success.

One of the most challenging factors in a project like this is retaining a service provider that can supply all of the necessary elements for a successful, standards-compliant repair or modification.

An Engineering Department, Certified Welders, a Mechanical Polishing crew to polish the final surface to the desired finish, in addition to a Surface Finishing crew to complete the electropolish and/or passivation requirements, are all essential.

It’s rare to find a single provider that can accomplish all of these steps. And yet, working with multiple providers can often lead to difficulty in resolving any issues, questions or concerns that might arise during the project.

Working with a single company,  qualified to complete the entire process from end-to-end, ensures that you have clear communication, accountability and consistent practices applied to your project. When it’s done, you have confidence the vessel is both safe and meets to the required standards when the testing is complete.

Testing your service provider’s qualifications

When selecting a provider, keep these details in mind:

• Drawing and the U-1 Report

The drawing must be reviewed to determine the design is adequate for the modifications or repairs requested.  The U-1 Report will give information not found on the drawing about the testing that was performed originally or any modifications that have been done since it was originally manufactured.

• Qualifying a Welder

The welder must be certified to weld the material (Stainless Steel) and qualified by ASME Division I Section IX Welding, Brazing, and Fusing Qualification.

• Electropolishing and Passivation

The work affected areas may require Electropolishing and/or Passivation. The area should be Electropolished according to ASTM B912 and Passivation according to ASTM A967 to ensure the desired finish and proper certifications.

• Testing of repair

The testing must be witnessed by an Authorized Inspector from The National Board of Boiler and Pressure Vessel Inspectors (NBBI)

• Welding the repair tag on the vessel

The repair tag is placed as close as possible to the area on the tank with the original tag with the serial number and National Board number when it is welded to the vessel.

Ensuring you have the right personnel performing the work to modify or repair a pressure vessel ensures your equipment is safe to perform as intended.

We all want our products to shine over the competition’s.  But, are you having trouble getting the best surface finish on your stainless steel equipment?  There are plenty of factors that can contribute to – or even prevent – finished surfaces from achieving the best possible finish or shine.

When parts processed in February, then the next order in July and a final order in November, it’s not unusual that their consistency and finish will noticeably vary. So, why do they look different?

Variables that contribute to consistency or uniformity while electropolishing include, amps, process time, fixture, position and electropolishing solution.  For instance:

• If amps are too low, the parts will have a dull or uneven finish; too many amps will cause micro pitting – also known as “orange peel” or ”frosting”.
  
• Process times vary depending on the size of the part, its thickness, and the configuration or shape of the part.
• While securing the part to the fixture in the same way every time seems like a simple matter, wear on the fixture itself can cause the current to arc, leaving a burn mark. Even something as simple as insufficient current flowing through the part will leave dull areas or a bullseye pattern in the center of the part.
  
• The layout of the fixture and the angle at which the part is positioned in the electropolishing solution can cause gassing. When gas bubbles form during the electropolishing process and run along the part, this prevents the electrolytic solution from making contact with the surface, creating an area of weakness that will not receive the full electropolishing process.
  
• Electropolishing solution can vary within an acceptable range. The interaction of the solution with the amps, process time and fixture can cause finish variation if not tightly controlled.

With this many variables, how can you ensure your parts will look great every time?  This is where a process control plan is critical to consistent results. When the amps, time, and fixture information are recorded, this helps ensure the same finish on every part, every time.

A second crucial area is the electropolishing solution. The solution must be examined by a chemist regularly and throughout the process. This ensures the solution remains within the ranges that are required to achieve the desired results.

When process control plans and proper chemistry are combined by an expert service provider, your products will shine above the competition with the desired finish every time.

Let’s talk about “rouge” (French for ‘red’) and I don’t mean the cosmetic term…

Rouging is a symptom of corrosion that occurs on stainless steel due to iron contamination.  Often unpredictable and imperfectly understood, the rouge is composed of corrosion products that include hydrogen and iron oxides in different states of oxidation.

Specific colors (or rouging) vary depending on the type of iron oxidation and is thought to be the result of a momentary deterioration within the passive surface. Another theory connects rouging to the interaction of passive layers that are high in chromium with water.  The resulting corrosion depends on the chemical composition of the steel and its operating environment.

There are fundamentally three types of rouging:

• • Type 1 – Red, Orange, Brown – This is the most common. Type 1 is rich in iron oxide with crystals forming on the surface of the metal. This type can be easily wiped off, but can also be dislodged while the product is being processed resulting in particulate contamination. These crystals start out at sizes smaller than a micron, but can easily grow to measure 100 microns (0.1mm).
  • Type 2 – Gold, Red, Brown – This type of forms at the site it is discovered, and if dislodged, it may reveal the bright surface of the stainless steel underneath. It is generally caused by the presence of chlorides in the water and it often appears on surfaces where the passive layer has become weak or where passivation was never performed.
  • Type 3 – Gray or Black – Also known as “scale” and dependent on the surface where it appears, this rouge is unique to high temperature, high purity steam systems, and is a form of magnetite. Type 3 typically gets darker as it grows and is formed by the iron interacting with hot water vapor binding with the oxygen to form a ferrous oxide, which gives it its black color, along with ferric oxide. When on a rough surface such as un-passivated, mechanically polished steels, it may appear loose and powdery. On a smooth surface, it can be shiny and is often detected when it appears on filters or autoclaved items.

There are various consequences from rouging that are a major concern including:

• Unsanitary finish on the surface of the metal – leading to contamination of the product being produced.
• Equipment malfunction – if left untreated, rouge can lead to structural damage of components or full even system failure.
• Process failure to meet specification – may lead to fines from government regulators.

Solution:

• Type 1 – This can simply be removed via a little ‘elbow grease’ and a specific non-abrasive chemical treatment then passivated for protection.
• Type 2 – It can be harder to remove than the similar-looking Type 1 rouge. It cannot simply be wiped off, but be treated with a de-rouging process. More severe cases may require chemical electropolishing to completely eliminate it from the surface. Regardless of the cleaning process used, the surface must be passivated afterward to restore the passive layer which will have been damaged by the rouge as well as the removal process.
• Type 3 – It may have a relatively high silica content which makes it more resistant to the usual chemical treatments. Often, more aggressive chemical treatments needed as well as mechanical polishing or electropolishing. Passivation is also an essential step to be taken after de-rouging.

These solutions can be completed by your maintenance team if they have the capabilities or through on-site service providers with mechanical polishing, electropolishing, and passivating capabilities.