Tubular NDT (
nondestructive testing) is the application of various technologies to detect anomalies such as
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
and manufacturing defects in
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
lic
tubes
Tube or tubes may refer to:
* ''Tube'' (2003 film), a 2003 Korean film
* ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom
* "Tubes" (Peter Dale), performer on the Soccer AM television show
* Tube (band), a ...
. Tubing can be found in such equipment as
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, centr ...
s and
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...
s. To carry out an examination ''
in situ
''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...
'' (i.e. examination of the tubes in position, where they are installed), a
manhole
A manhole (utility hole, maintenance hole, or sewer hole) is an opening to a confined space such as a shaft, utility vault, or large vessel. Manholes are often used as an access point for an underground public utility, allowing inspection, m ...
cover is usually removed to allow a technician access to the tubes. Alternatively, a tube bundle may be removed from a heat-exchanger and transported by
forklift to a maintenance area for easier access.
The usual means of examination is to insert some type of probe into the tubes, one at a time, while data is recorded for later interpretation. The technologies listed below (ECT, RFT, IRIS, and MFL) are all able to detect defects on the outside of the tube from the inside. The tubes must be clean enough to allow passage of the probe: deposits of debris, rust, or scale may have to be removed by chemicals or
pressure washing
Pressure washing or power washing is the use of high-pressure water spray to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles and concrete surfaces. The volume of a mechanical pressure w ...
. In
water-tube boiler
A high pressure watertube boiler (also spelled water-tube and water tube) is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which boils water in the steam-gen ...
s, the tubes may be examined from the outside when the boiler is shut down, often using
ultrasonic testing
Ultrasonic testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. In most common UT applications, very short ultrasonic pulse-waves with center frequencies ...
.
Common methods
*
Eddy-current testing
Eddy-current testing (also commonly seen as eddy current testing and ECT) is one of many electromagnetic testing methods used in nondestructive testing (NDT) making use of electromagnetic induction to detect and characterize surface and sub-surfa ...
(ECT) is commonly used on non-
erromagneticmetals and alloys such as copper, brass, and
copper nickel
Cupronickel or copper-nickel (CuNi) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. The copper content typically varies from 60 to 90 percent. (Monel is a nickel-copper alloy that contains a minim ...
. Variations on ECT are partial saturation ECT and magnetic biased ECT, both of which use magnets to allow ECT to operate in lightly ferromagnetic materials or in thin-wall ferromagnetic tubes.
*
Remote field testing (RFT) is used on
erromagneticmaterials such as carbon steel.
*
IRIS (Internal rotary inspection system) can be used on all types of metal tubes. IRIS is very slow, but very accurate, and is often used as a back-up to a remote field examination.
*
Magnetic flux leakage
Magnetic flux leakage (TFI or Transverse Field Inspection technology) is a magnetic method of nondestructive testing that is used to detect corrosion and pitting in steel structures, most commonly pipelines and storage tanks. The basic princip ...
(MFL) testing is used on carbon steel tubes, although it tends to be less accurate than remote field testing.
[K. Krzywosz and G. Dau. "Comparison of Electromagnetic Techniques for Nondestructive Inspection of Ferromagnetic
Tubing," ]
Materials Evaluation
{{Webarchive, url=https://web.archive.org/web/20060923010957/http://www.asnt.org/publications/materialseval/materialseval.htm , date=2006-09-23 '', Vol. 48, No. 1, January 1990, pp. 42–45.
References
Sources
*
Heat exchangers: Monitoring and maintenance
* H. Sadek, ''NDE technologies for the examination of heat exchangers and boiler tubes – principles, advantages and limitations,'
PDF 2.1 MB.
* Fathi E. Al-Qadeeb, ''Tubing Inspection Using Multiple NDT Techniques''
PDF 118 kB.
Nondestructive testing