Canadian firm inspects heavy wall pressure vessels fast and cost-effectively. Tim Auger, president of Custom Pipe Services shares his experience with AIS.

Custom Pipe Services, based in Leduc, Alberta, Canada, is an inspection services company servicing the Canadian pipeline industry. One of their specialties is the inspection of heavy-wall pressure vessels used in refineries, breweries, and reactors.

Custom Pipe Services owns an AIS eight-channel NB-2000MC and a motorized Mag XY Scanner. The scanner is equipped with a TOFD Frame to examine heavy-wall pressure vessel welds in accordance with ASME Code Case 2235, "Use of Ultrasonic Examination in Lieu of Radiography.”

Q: What are some of the reasons why clients come to you for inspection services?

A: Industry regulation and code compliance is certainly a big reason why companies perform inspection. But a lot of it is self-interest, too. End-users of the inspected equipment want their workers to work in a safe environment. They also don’t want their welds to fail, because it would cost a lot of money. For instance, we inspect drill pipes. If one of those were to fail in a drilling operation, it could cost the operator half a million dollars.

Q: Why do you use ultrasound inspection instead of radiography to inspect heavy-wall pressure vessels?

A: Pressure vessels can exceed four inches in wall thickness. Only ultrasound gives us the ability to do internal inspection accurately. Radiography is limited in this particular application. It has a hard time resolving small defects and certain planar defects where the weld preparation is primarily vertical. Also with radiography, there are cost and safety issues. The thicker your material, the larger the x-ray source. If we’re in a manufacturing facility, we don’t have to shut down the line and clear room to protect the workers. This would cost our customers a lot of money.

Q: When performing an inspection, the area of greatest interest is usually the weld volume and the heat affected zone. Explain in greater detail the type of defects that AIS allows you to detect.

A: The two major types of defects that we are interested in are planar and volumetric. Plan defects refer to cracks or lack of penetration, where the weld metal did not fuse to the base metal properly. We classify these as critical. Again, radiography has a hard time picking these up. Volumetric defects occur when there are air pockets in the weld. It can also be a slag inclusion that occurs when the weld is not properly cleaned and prepared between weld passes. Volumetric defects are considered to be less serious.

Q: Aside from detecting these defects, can you measure and disposition them on the spot?

A: Yes. When examining heavy-wall pressure vessel welds in accordance with ASME Code Case 2235, all indications are assessed as acceptable or rejectable based on their height (through wall dimension), length (along the weld), and where the defect is embedded or surface connected. Once these dimensions are determined, they are algorithmically compared against the Code and assigned a go-no-go value.

The AIS system uses sophisticated techniques to measure these dimensions. The most difficult and critical dimension to measure is the height of the indication. AIS does this by measuring the forward scattered diffraction tips via a TOFD (time of flight diffraction) examination. If the TOFD examination results are unclear, then the AIS system resorts to measuring the height using a backscattered tip diffraction method which requires the transducer to be rastered across the weld. Both techniques are well proven and provide reliable results.

Q: How would you describe the return on investment of your AIS system?

A: It’s hard to put a number on it. But for sure, AIS has helped us market and expand our business. We would not be inspecting heavy-wall pressure vessels, if it weren’t for their automated UT system. I can tell my clients about AIS and that their equipment is used to inspect welds on pipelines and pressure vessels all around the world – and in very harsh conditions. I know the Chinese are inspecting 13-14 inch walls. That’s good enough for my clients. The quality of the AIS system is well known. With the recorded inspection data, we can analyze and present accurate findings to our clients, and they can do the same to confirm or assess our work. The results are trustworthy and this goes a long way to cementing our relationships with clients.