Plant Integrity & Diagnostics -> Vessel Integrity Inspection

The oil, gas and petrochemical industries use a wide range of vessels including tanks, separators, towers, columns and many more. Assessing and maintaining the structural integrity and operational efficiency of these vessels is a key element in optimising production, pricing and profitability. Roxby Services can provide the technology and expertise to carry out these tasks professionally and cost-effectively.

In meeting our customer needs in this field, we make use of a variety of technologies including gamma scanning and the Neuscan detector. We also apply a number of non-destructive testing techniques such as ultrasonics, magnetic particle inspection and dye penetrant inspection to name a few.

Despite the superior quality of our equipment, the extensive experience of our fully qualified personnel and the high level of service we provide, our charges are highly competitive and likely to provide significant cost-savings.

Gamma Scan

Gamma scanning is used to determine what is happening inside a vessel and assess its operating characteristics. It is most often used on trayed columns and packed bed towers, but can be used on a wide range of vessels.

A small gamma ray source and an electronic detector are positioned on opposite sides of the vessel to be scanned. As they move along the outside of the vessel, gamma rays travel through the vessel, are moderated by the contents and are then counted by the detector. In this way, a density profile is generated.

On trayed columns, potential problems can include pressure surges during start up and gradual fouling leading to pressure differentials across trays. Gamma scanning can identify and diagnose a variety of problems such as damaged, blocked or missing trays and internals, as well as determining the height of aerated liquid on each tray, the location of any flooding, entrainment, weeping or foaming, the height of liquid on chimney and draw trays and the level of liquid in the base of the column.

Packed bed towers can also be evaluated using gamma scanning, which can check correct placement and levelness of demisters, distributors, trays and bed tops, measure base liquid levels and levels on chimney trays and draw pans, and pinpoint the location of hold down and support plates. Gamma scanning can also identify damaged, crushed or settled packing, the location and extent of any fouling or liquid maldistribution. For some of these tasks, a grid scan, consisting of a series of four scans across the bed, is necessary.

Gamma Scanning is used to determine

• Damaged or missing trays and internals
• Height of aerated liquid loading on trays
• Height of liquid in downcomers
• Location of entrainment and liquid weeping
• Location and characteristics of foaming
• Location and extent of flooding
• Fouling of packing or catalysts
• Flow maldistributions in packing
• Base liquid levels

Nuescan Detector

The Neuscan detector is a lightweight, hand-held tool used for accurate level measurement of all common hydrogen-bearing substances in tanks, separators and other vessels, whether standard, curved, insulated or heavy-walled. It can be used with water, hydrocarbons, acids, bases and other organic liquids.

The detector is a high quality, professionally manufactured, sealed unit. This is of particular importance in terms of health and safety as radioactive isotopes are used in the process. The sealed radioactive source is mounted next to a very sensitive Helium-3 slow neutron detector tube. The source emits fast neutrons which penetrate the vessel wall, interact with the hydrogen atoms in the contents and lose energy. Some neutrons are then backscattered to the detector as slow neutrons. Differences in hydrogen content allow the detector’s count rate meter to determine the boundaries between solids, liquids and vapours, and even the interfaces between two liquids.