Knowledge Centre

Glossary

3D Scans

The latest laser technology can be used to provide accurate 3D images. This can be useful for storage tanks where shell distortion is important, such as floating roof tanks. The scan can also be used to accurately measure the tanks capacity (Calibration).

ACFM

Alternating current field measurement (ACFM) is an electromagnetic technique used for the detection and sizing of surface breaking cracks in metallic components and welds. It has the advantage of being able to inspect through paint and coatings and is especially beneficial for testing welds under coated tank floors.

Acoustic Emission

AE is a process whereby sensors located around a test item (Such as a storage tank) listen for stress waves caused by the effects of stress on items such as cracks, leaks and fibre breakage in composites. The technology is capable of “hearing” very small defects, and uses triangulation to pinpoint where the source is located. The system is best used as a screening tool to pinpoint areas for in-depth NDT such as UT or MPI.

API 510

(Pressure Vessel Inspection Code: In-Service Inspection, Rating, Repair, and Alteration). First published in 1958 as a recommended practice, API 510 is regarded as the benchmark for the inspection and repair of in service and out of service pressure vessels and pressure relieving devices. The code covers any pressure vessel constructed to known or unknown codes and provides limits for minimum thickness and maximum working pressures as well as providing parameters for the repair of any defective areas.

API 570

(Inspection, Repair, Alteration, and Rerating of In-service Piping Systems). First launched in 1993, API 570 is now in its 4th edition. The document is classed as a statutory code in the US but is seen as a best practice for the inspection and repair of piping systems elsewhere. The document provides guidance on common issues associated with process piping systems as well as formulae to be used for establishing safe operating limits. It provides recommended inspection intervals and is very useful when repairs are required.

API 653

(Tank Inspection, Repair, Alteration, and Reconstruction.) First published in 1991 by the American Petroleum Institute, API 653 is in its 5th edition. Considered to be the main code for the inspection, repair, alteration & reconstruction of above ground storage tanks outside of Europe, the document takes the form of a code rather than a guide (As EEMUA 159). The document is primarily to be used for the inspection of tanks constructed to API codes 650 or 620. Experience has shown API 653 to be the preferred document for repairs of above ground storage tanks.

Bund Capacity Assessment

The capacity of a tank bund should be large enough to accommodate the inventory of the tanks located within it. Limits exist which stipulates the minimum allowable capacity of a tank bund should there be a loss of inventory from one or more tanks. To ensure a bund meets existing limits, it is necessary to measure the bund dimensions and then compare the bund volume to the total tank inventory volume.

Corrosion Mapping

Corrosion mapping is a non-intrusive UT technique for the detailed thickness measurements of corroded surfaces. As its title suggests, the equipment produces maps of the area tested to show the location & depth of internal pitting. The process is especially useful on pressure vessels but can also be used on storage tanks or pipework.

EEMUA 159

(Above ground flat bottomed storage tanks – a guide to inspection, maintenance and repair.) The Engineering Equipment and Materials User Association publication 159 has been around since 1994 and is now in its 5th edition. The document is intended primarily to assist in the establishment of essential inspection & maintenance requirements for above ground, vertical, cylindrical steel storage tanks, and as such provides comprehensive guidance on acceptable limits, key design features, common experienced problems and repair methods. It is used throughout Europe and is considered by the HSE as the benchmark for the inspection of above ground storage tanks. The document is mainly focused towards tanks constructed to BS or EN codes, but can also be used for tanks constructed to API codes.

IRIS

Internal Rotary Inspection System is a UT based tool for the inspection of tubing or piping wall thickness for corrosion or erosion. The system uses a small ultrasonic probe which is inserted into the tube and reflects off a rotating mirror. The ultrasonic signal passes through a medium (Usually water) whereby it enters the wall of the tube. The signal is reflected back, and the thickness then calculated by the system. The technique is very accurate but is heavily dependent on having a clean internal surface on the tube, keeping the probe in the centre of the tube and requires a water supply.

ECT Tube Testing

A very accurate system for the detection of defects in non-ferrous materials. A probe is inserted into the tube, which in turn creates Eddy Currents in the tube wall. Any defects in the tube wall breaks the eddy currents path and are detected by sensors. These signals are then compared to calibrated signals by the system allowing accurate defect severity measurements.

Ferrite Measurement

The amount of ferrite in and around the welds of austenitic and duplex stainless steels is important for both the structural integrity & corrosion resistance qualities of the test piece. Low ferrite content leads to a weak joint, too high a content can reduce the corrosion resistance of the material as well as the ductility & toughness.

Hardness Testing

A materials hardness can be used to determine its toughness, resistance to wear and to predict its tensile strength. There are a number of scales by which to measure these characteristics and each one is influenced by differing requirements. We can conduct hardness testing to Vickers, Brinell or Rockwell scales.

Holiday Testing

A holiday is a breakage or hole in a protective coating such as paintwork or lining. There are a number of ways for finding holidays depending on what component is being tested, but each involve applying an electrical current to the test piece. The current will earth in the presence of a holiday, triggering an alarm on the test system.

Level Survey - Tank Floor Profile

Tank floors are primarily just a membrane, and should they be correctly supported, are under very little stress. However, should the foundation under the floor undergo excessive settlement, this will result in stresses to the fillet welds of which the floor plates are joined. Should these stresses prove to be excessive, this will result in a failure of the welds and a loss of inventory. A tank floor profile survey can help detect excessive settlement before it becomes an issue. However, to be conducted properly, the tank floor needs to be under weight to ensure it takes the contour of the foundation. This is achieved by filling the tank with a few inches of water.

Level Survey - Differential Shell Settlement

Depending on the type of foundation, it is common for storage tanks to “settle” into their foundations and this is often accommodated when designing & construction a tank. If the settlement is uniform throughout the diameter of the tank, the settlement is usually of little consequence. However, should the settlement be concentrated to one area, this can induce localised stresses in the tank shell which can lead to further complications. A simple survey can be undertaken to check for differential settlement and the amount of settlement assessed to ensure it is within acceptable limits.

Level Survey – Floor Edge Settlement

Storage tank floors occasionally settle at the edge due to the weight of the shell & roof impacting on the foundation. EEMUA 159 stipulates limits for the amount of allowable edge settlement.

Level Survey - Tank Floor Profile

Tank floors are primarily just a membrane, and should they be correctly supported, are under very little stress. However, should the foundation under the floor undergo excessive settlement, this will result in stresses to the fillet welds of which the floor plates are joined. Should these stresses prove to be excessive, this will result in a failure of the welds and a loss of inventory. A tank floor profile survey can help detect excessive settlement before it becomes an issue. However, to be conducted properly, the tank floor needs to be under weight to ensure it takes the contour of the foundation. This is achieved by filling the tank with a few inches of water.

Level Survey - Tank Verticality

EEMUA 159 provides limits for the amount of acceptable “Out of Verticality” of a storage tank. Tank verticality is assessed by first measuring the angle of the shell, then comparing this to the calculated limits set out by EEMUA 159.

LRUT

Long Range Ultrasonic Testing is a technique which allows large lengths of pipeline to be screened for wall losses. Typically, lengths of up to 100m above ground & 10m below ground can be tested (Depending on various factors) by inducing a sound wave along the length of a pipe. Echoes, including corrosion, are measured by an array of probes for both depth & distance.

PEC

Pulsed Eddy Current is a technique which can be used to measure carbon steel wall thicknesses through layers of insulation, fireproofing or other coatings. The technique is now commonly used to detect CUI of pipelines, vessels or storage tanks.

Phased Array

Phased array is an ultrasonic technique which utilises an array of transducers to allow the accurate sizing of flaws, primarily in welds.

Pipework Corrosion Scanning

Depending on pipe diameter, surface condition & sensitivity required, there are a number of ways of scanning pipework for internal wall losses. From a simple scan using a 0º UT probe, a screen using LRUT to a detailed scan by phased array or guided wave, we can assist in the selection process & provide the necessary equipment & expertise to ensure your pipework is thoroughly inspected.

PMI

Positive Material Identification is used when it’s important to know the characteristics of a material. The process uses either x-ray fluorescence or optical emission spectrometry to identify the composition of metals, which is then referenced to known materials, thus establishing the test material.

Remote Field

A probe is inserted into the tube which then generates a magnetic field in the tube wall. Corrosion causes a build-up of the magnetic field, which is detected by sensors on the probe. The system is able to compare the signals to calibrated signals, thereby giving a wall loss severity. The system can only be used on ferrous materials.

Remote Visual Inspection

The use of borescopes or endoscopes for inspection of hard to reach areas such as inside tubing or piping.

Repair Guidance

Documents such as API 653, API 510, API 570 & EEMUA 159 give guidance on acceptable ways of repairing defects in process plant. We are qualified & experienced to be able to provide guidance on how to repair defects thus keeping your plant code compliant.

RBI

Risk Based Inspection is a process whereby both the potential & consequence of failure of process plant is assessed. This allows the owner to focus on items found to be high risk and schedule inspections accordingly. There are many models for RBI, however, we are able to offer assistance for conducting RBI assessments to both API 580 & EEMUA.

Rope Access

Rope access is now established as a satisfactory means of accessing areas inaccessible for inspection by ropes. Rigorous procedures ensure that personnel are competent, and equipment is fit for use, ensuring the technique has a good safety record.

Secondary & Tertiary Containment Assessments

Secondary & tertiary containment is often overlooked. However, the incident at Buncefield showed the importance of both secondary & tertiary containment. We can conduct assessments of your facility to ensure the secondary &/or tertiary containment systems are suitable & comply with applicable regulations.

Surface Eddy Current

Probes are used to generate eddy currents in the test piece for the detection of surface breaking or sub-surface defects in metals. The process can be used on ferrous or non-ferrous materials.

Tank Floor Scans

The technology used to inspect tank floors is continually evolving but is based primarily on 2 technologies. MFL (Magnetic Flux Leakage) and ECT (Eddy Current). Both technologies generate a form of magnetic field in the plate being tested. Corrosion causes changes in the field which is detected by sensors, analysed by software and usually displayed on a laptop in colours relating to the amount of change (To the magnetic field) detected. Like any specialised inspection technology, the system is dependent on an experienced, skilled technician. Specialist Inspection utilise the latest MFL system.

Tank Shell Inspection

The tank shell is the main area of containment for a storage tank and as such it is critical to find and assess any corrosion/erosion which could affect the shell’s fitness for service. The most common means of inspecting storage tank shells is by UT thickness measurements of the plate thickness. These figures are then entered into calculations which allow an assessment to determine if the shell can take the loads it is being subjected to. Access to the shell can be via rope access, MAWP, scaffold or tank crawler. Systems are also available which allow scans of the shell to detect thinning of the plate.

Unmanned Aerial Vehicles

Unmanned aerial vehicle (Aka Drones) technology is rapidly moving forward and can be a useful inspection tool for hard to reach areas, such as the upper sections of storage tanks. The technology is being recognised by EEMUA as a viable means of conducting close visual inspections of hard to reach areas via high definition cameras.

UT Thickness Surveys

Ultrasonic thickness is a well-established technique for measuring the thickness of solids (Such as plates & pipes) using ultrasound. It does have some limitations but is critical when establishing the condition of process plant and for the information required to conduct FFS calculations.

Written Schemes of Examination

Under the Pressure Systems Safety Regulations 2000, users and owners of pressure systems (>0.5 bar) are required to demonstrate that they know the safe operating limits (principally pressure and temperature) of their systems, and that they are safe under those conditions. They need to ensure that a suitable written scheme of examination is in place before the system is operated. They also need to ensure that the system is actually examined in accordance with the written scheme of examination. Although the legal requirement is for systems within the PSSR, maintaining a WSE for non PSSR assets is seen as good practice. We can help with the details & creation of WSE’s.

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