Glossary of tube inspection, cleaning and decoking terminology

An untethered tool which has degrees of onboard power, sensors, logic and memory to enable the collection, retrieval and subsequent analysis of internal and external data from inside a pipeline.

The pig is propelled through a tube system or pipeline by either product flow or flow facilitated by external pumping. Typically water, the driving medium may be liquid or gas, depending on the tool technology and client requirment.

The process by which a metallic surface is degraded, which if unchecked can lead to a compromise in integrity and potential failure.

There are numerous mechanisms and threats to consider, but simplistically corrosion may manifest as a) discrete pitting b) general wastage or c) cracking.

The typical wet corrosion cell consists of four components a) anode, b) cathode c) an environment which supports ionic exchange, and d) electrical connectivity between anode & cathode for the movement of electrons ie. an electric current.

Corrosion can be accelerated by temperature, aggressive compounds in the environment, concentration gradients eg. under deposits, crevices etc.

The manifestation and progression of a crack caused by stress cycles on a susceptible material. Progress and severity can be influenced by stress frequency and amplitude as well as material properties. Corrosion is likely to exacerbate this effect.

Progressive wear of a material surface caused by certain flow conditions typically in the presence of suspended particles.

Corrosion is likely to exacerbate the effect.

A progressive, plastic deformation of material over time and under stress. Such stresses may result from high temperature steam or internal pressure.

Creep often occurs at levels below the material yield limits.

A physical barrier used to separate eg. a steel pipeline surface, from the adverse effects of the environment. The barrier is typically used for corrosion protection but also from mechanical damage, or erosion.

Coatings may be depositions, wraps, sprayed or hand applied. There are standards which dictate the surface cleanliness, manner of application and curing as well as the chemical composition.

The deliberate dosing of process fluids can improve the corrosion resilience of the metal substrate.

Inhibitor application may be continuous or facilitated by batch. The inhibitor may be organic film forming or an inorganic compound which encourages passivation.

Other forms of dosing can serve to scavenge ie. to manage the content of the process fluid.

Broad terms use to characterise corrosion related wastage or cracking. They may also represent other abnormalities such as weld intrusion.

It is usual to try and define the nature and extent of the effect as well as the location. Where a tube, pipe or pipeline is concerned location should consider: internal, external, axial position and orientation.

An engineering assessment used to determine if an asset is safe for continued operation. Assessments are prescribed by API 579-1/ASME FFS-1 standard.

Three levels of assessment are considered:

Level 1: Basic screening using minimal inspection data

Level 2: A more comprehensive assessment and calculative in nature

Level 3: Involves advanced techniques like Finite Element Analysis (FEA) typically undertaken by suitably qualified personnel. This level evaluates more complex load/damage scenarios.

An assessment undertaken to predict the future serviceability/integrity of an asset. The method takes into consideration performance criteria, operational history, material degradation, and non-destructive testing (NDT) data.

The process by which petroleum coke is formed by thermal cracking of hydrocarbons. Coke can be prematurely or inconveniently formed in process tubing leading to the requirement for a ‘decoking’ intervention. The term “coke” is broad, likely to contain inorganic material and varying in hardness.

As well as compromising process flow, coke acts an insulator compromising the transfer of heat flux to the product carried inside the process tube. To maintain heat transfer performance as coke is formed it becomes necessary to increase the amount of fuel gas burned, thus increasing tube skin temperature which can de-nature tube metal leading to degradation and potential rupture.

Coke scale can also exacerbate corrosion beneath its deposit, in particular where aggressive compounds such as sulphur are present.

The process by which scale forms within a process. Minerals such as calcium, magnesium within the feed water can precipitate on the tube surface creating a fine scale.

As well as compromising process flow the mineral scale acts an insulator compromising the transfer of heat flux to the product. To maintain performance it is necessary to increase the amount of gas burned thus increasing tube skin temperature which can de-nature process tube metal leading to material degradation and potential rupture.

Mineralised scale can also exacerbate corrosion taking place beneath deposit.

Heat Recovery Steam Generators (HRSG) and Once Through Steam Generators (OTSG) take waste heat from eg. gas turbines or other industrial processes and utilise this to generate steam.

The steam is typically used for other plant process or possibly for down-hole injection to reduce viscosity of recovered crude.

A sizeable equipment asset in which heat flux is transferred to a process flow.

Heat is typically provided through gas firing of a number of burners. Heat flux is transferred via radiation and convection ie. radiant zone, convection zone.

The process flow is typically contained in a serpentine coil arrangement, often with multiple ‘passes’ or ‘coils’.

The above is contained within a thermally lined fire box with exhaust gases leaving via chimney.

There are numerous types of fired heaters depending on the nature and intent of the process eg. crude heater, delayed coker, visbreaker, vacuum etc.

A phenomenon whereby a tube/pipe is distorted and loses its concentric and uniform nature. This maybe caused mechanically eg. mandrel bending or heat stress leading to a plastic strain.

Consequences can be out of roundness, bulging, variations in wall thickness.

Insulation materials are often applied to piping/pipeline surfaces to manage heat transfer. The insulation is often clad to hold the insulation in place and protect it from the environment.

Moisture from condensation or leak paths can permeate and wet the steel/insulation interface, facilitating a corrosion cell. The presence of aggressive ions and oxygen gradients can lead to accelerated and localised external corrosion which typically remains undetected.

An inspection method that uses high-frequency sound waves to measure internal diameter and material wall thickness.

Through the use of a couplant, eg. water/gel, sound waves travel to and into the tube material. Using time of flight calculations distance can be measured and defects identified.

A more advanced inspection method that uses multiple ultrasonic elements pulsed at specific time delays. Electronic phasing permits the steer, sweep, and focus of acoustic waves/beams at different angles without moving the probe.

Magnetic Flux Leakage

As the MFL pig passes through, the pipe surface is saturated with magnetic flux. In the presence of defects eg, wall loss, cracking etc. the magnetic field becomes distorted and there is flux ‘leakage’ out of the material. On board sensors measure and map the leakage to qualify and quantify defect(s).

Electro-Magnetic Acoustic Transducer

The EMAT tool is a non-contact and couplant-free ultrasonic testing method. Acoustic waves are generated using intersecting magnetic fields.

Recognised qualifications for inspection technicians.

A combination of piping and pipelines constructed for the purposes of testing, training and demonstration. Test loops may contain defect tubes to promote evaluation of inspection and measurement tools and operating techniques.

The test loop is typically designed to mimic process flow conditions and therefore be as close to a real world condition as is reasonably possible.

A bespoke section of pipe with known defects machined into the pipe surface, internally and/or externally. Such defects maybe grooves or pits. Crack-like defects can also be introduced.

The defect tube is typically placed into a Test Loop and used for evaluating tool performance and operating techniques.

As Low As Reasonably Practicable – a principle which sets the level of frequency that something will or won’t happen.

The term practicable is intended to allow a freedom that while every eventuality can arguably be avoided there must be a level at which risk becomes acceptable, often in financial or time-based terms.

A well-known and widely used technique used to mitigate the effects of corrosion.
Two techniques are commonplace.

1) Impressed Current – a transformer rectifier is used to create an ‘opposing’ electrical current to ‘offset’ the detrimental corrosion reaction
2) Sacrificial Anode – an element/alloy more ‘base’ than eg. the host pipeline which corrodes in preference to the host

A mechanical pipeline joint which is designed to prevent electrical continuity between the mating pipe sections.

Such a joint is often used to create isolation where cathodic protection systems are deployed or where there are dissimilar materials.

A valve (typically a ball valve) installed ‘in-line’ with process flow which can facilitate the entry/exit of a single bodied mechanical or smart pig. The valve chamber is accessible when rotated perpendicular to the flow and the chamber bled/vented. A bypass is typically utilised to maintain process flow whilst the intervention is made.

Convention is such that process flow is homogeneous i.e. a single product.

When the product is made up of more than one component the flow is termed multiphase. Typically this could be a mixture of oil, water and gas. Relative specific gravity, velocity and turbulence will determine the degree of phase separation or mixing.

The progressive removal of coke deposits using mechanical pigs under controlled water flow. The tools and techniques are found to be quite variable amongst those who practise this procedure.

The context relates to the ability for the activity of mechanical decoking/descaling and associated smart pigging carried out by the same contracting company. Use of one set of machinery and equipment operated by colleagues in one company presents a seamless flow of work.

Such a service removes awkwardness of contractual interfaces which typically requires an increased level of administration, as well as leading to potential conflict between contractors which may cause delay and additional cost.

The use of high velocity small particles of dry ice (carbon dioxide) as a form of abrasive blasting. The use of thermal shock and kinetic energy is designed to clean material surfaces.

The managed process of introducing and circulating chemicals into a process for the purpose of cleaning. The process must be strictly controlled to ensure the safety of operators and operations, and in particular the process of removal and ethical disposal.

An historic coke removal process involving the introduction of steam and air flow along with heating of the coil.

The process serves to facilitate the combustion and thus removal of coke. Although the process can be effective, a high level of skill and experience is required to monitor skin temperatures and carbon dioxide levels. Use of this method has potential for hazard and can be unpredictable in duration.

A coke removal process involving the introduction of steam, fired heating and water cooling. The decoking operation is thus facilitated by thermal shocks, literally to shatter the coke layers.

Typically only used as an interim measure, this process can work one pass at a time, thereby allowing the heater to be ‘on line’.

A dense coating (usually concrete) applied to pipelines to counter buoyancy effects and ensure a subsea pipeline remains on the sea bed and does not float.

Where a pipe section is found to be unsupported, typically associated with undermining on the sea bed; the unsupported section is said to be a ‘span’.

A pipe barrel dead-leg out of the line of process flow which serves to launch and receive pipeline pigs. The trap will contain a door, isolation and bleed functionality.

A generic term for a pipeline mechanical pig used for gauging or cleaning purposes. The term may also be used for an intelligent/smart pig.

Single / Double Pumping Unit. A purpose built pumping unit typically used for mechanical decoking. Numerous companies have built and branded such machines. The origins of such go back to the early 1990s when the principles of mechanical decoking were first established.

There is significant variation in the design, build, maintenance and use of such machines.

The simplest of mechanical pigs used for proof of passage as well as facilitating activities such as dewatering or indeed as an aid to other pigging operations.

When used in mechanical decoking or descaling the pig is typically sacrificial and serves to provide an indication of internal pipe condition.

A mechanical pig fitted with a gauging plate (usually aluminium). This pig is used for ‘proof of passage’ with the gauge plate deforming to represent any inline anomalies such as weld intrusion or pipe/tube ovality.

A mechanical pig usually with several polymeric discs and or wire brush sets which is used to clean a pipeline. There are numerous designs to suit different applications and processes.

The tool is typically symmetrical in order that it can be used bi-directionally.

Direct Current Voltage Gradient. An above ground survey technique whereby it is possible to locate and evaluate size coating defects.

Close Interval Potential Survey. An above ground survey technique whereby it is possible to locate and determine the severity of corrosion.

A physical identifier located above ground which marks the location of a buried pipeline. The marker may contain information on depth and nature of process flow.

A physical identifier located above ground which marks the location of a buried pipeline. The marker may contain information on depth and nature of process flow.

A physical identifier located above ground which marks the location of a buried pipeline and has connections to pipeline to facilitate measurement such as for CIPS.

A device typically attached to a pipeline which will identify when a pig has passed the location concerned. Often use to confirm launch/receive, this device can also be used along the length of the pipeline.

A simple annotation which identifies the external diameter of a pipe and its nominal wall thickness. Pipe schedule tables are commonplace and readily searchable.

Process piping/tubing is often accessible by a simple flange fitting. There are a variety of flange types and rating.

On certain systems the process passes are attached to / suspended from a ‘common header’ as opposed to a conventional flange. The common header is a larger diameter pipe typically with domed ends which may have access flange plates.

Piping and Instrumentation Drawing.

A drawing which sets out schematically the layout of equipment and instrumentation, along with tag numbers and dimensions.

Internationally accepted symbols serve to annotate certain equipment items such as valves and switches.

An industrial fired heater used in petroleum refining and chemical processing. This features a radiant coil configuration, multiple parallel U-tubes that branch off from common inlet and outlet header.

The design is a low-pressure drop and so these heaters are specialized for high-volume, gas-phase processes such as catalytic reforming.

Simplistically an organic compound of carbon and hydrogen. Classification is based on molecular structure and the nature of bonds formed.

Saturated (single bonds). Alkanes like methane, ethane and propane. Formulae CnH2n+2

Unsaturated (at least one double bonds). Alkenes like ethene (ethylene). Formulae CnH2n

Unsaturated (at least 1 triple bond). Alkynes like ethyne (acetylene) CnH2n-2

Aromatic: Cyclic compounds containing ring structures such as benzene.

A concept or principle which can mean different things to different people. Corporations often use the term as a headline to an internal standard or policy where it maybe interchangeable with Asset Management or Asset Integrity Management.

In its simplest sense this can be considered to define a goal or set of parameters to ensure containment integrity and thus assure process safety.