NDT Testing Services
We offer the following NDT Services
Further information on each of the methods is described below.
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Ultrasonic Testing (UT)
Ultrasonic testing is a non-destructive testing method where pulses of ultrasound are introduced into the sample under test and by analysing the resulting echo or echoes an experienced operator is able to make a judgement of the quality of the part.
Some of the benefits of ultrasound are:
- Often cheaper than radiography, especially for large parts or high volumes.
- Can be advantageous over radiography on heavy sectioned parts or on dense materials.
- In many instances a satisfactory ultrasonic examination can take place with access to only one side of the part.
- Under some circumstances ultrasonic examination can take place whilst item under test is still in use, for example testing welds or wall thicknesses on pipework.
- Modern ultrasonic equipment is lightweight, highly portable and is powered by batteries and unlike radiography it poses no risk of ionising radiation to either the operator or people nearby.
- Accurate wall thickness measurements can easily be taken, often even under unfavourable conditions and with only one side accessible.
Some of the problems of using ultrasound are:
- The accuracy and correct interpretation of results is highly dependant on operator skill, judgement and experience. This risk can be greatly reduced by making sure detailed procedures and instructions are in place prior to testing.
- Often no permanent record of ultrasonic data is produced, so analysis at a later stage is not possible. Modern techniques are seeking to address this shortcoming but currently have limited applications, with pipe welds being the most common use.
Typical uses of ultrasonic testing method are:
Magnetic Particle Testing (MT or MPI)
- Testing of steel castings, looking for shrinkage voids, porosity, cracks, cold laps etc.
- Wall thickness checking of castings to ensure that any cores have not moved during the casting process.
- Testing of forged and rolled bar stock, looking for axial looseness, forging bursts,surface cracks, etc.
- Testing of rolled steel plate, looking for laminations and inclusions.
- Wall thickness checking of tanks, vessels and pipes.
- Testing of many types of welds for lack of fusion, lack of root penetration, cracks, porosity, etc.
- Checking of composite materials for thickness or incomplete bonding.
Magnetic particle inspection or testing is a method which can only be used on ferromagnetic materials, most commonly steel. The method works by either fully or locally magnetising the part and whilst the part is magnetised a small amount of coloured iron filings are applied to the area under test, this can either be in the form of a powder but more commonly in the form of a liquid suspension called magnetic ink.
Whilst the part is suitably magnetised any surface breaking defects (and some cases subsurface defects) will cause a disruption in the magnetic field. When the iron filings are applied they will accumulate around this anomaly and allow it to become visible to the operator.
Some of the benefits of magnetic particle testing are:
- A quick and relatively low cost method for finding surface breaking defects, especially good at finding surface breaking cracks.
- A flexible technique that can be used to inspect products in many different industries and has been used to find defects in items ranging from 400 ton castings to small TIG welds in steel pipe..
- Portable equipment can be used for on-site work.
- Indications found by magnetic particle testing are by and large fairly easy for the operator to detect and correctly interpret.
Some of the problems of using magnetic particle testing are:
- Only suitable for ferromagnetic materials, many types of stainless steel, and all types of aluminium, titanium, etc. cannot be inspected using the MPI technique.
- In order to fully test the part a magnetic field has to be set up in two perpendicular directions as the technique will only find flaws which cross the magnetic field lines.
- If correct procedure is not followed residual magnetism can sometimes be left in the part after testing, which may cause problems later on or in service.
- Correct interpretation of indications is down to operator skill and experience. Again, this risk can be greatly reduced by making sure detailed procedures and instructions are in place prior to testing.
Typical uses of the magnetic particle testing method are:
Penetrant Testing (PT or DPI)
- Detecting cracks, forging laps and other defects in fixings, bolts, rivets, etc.
- Surface breaking flaws in new and in-service fabrications, pipework etc.
- Finding cracks in gear teeth during the overhaul of gearboxes.
- Looking for cracks, inclusions, cold laps, porosity/gas, etc in steel and iron castings.
- Checking of repair welds in castings and fabrications for surface breaking defects.
- Confirming that cracks detected using other methods i.e. via ultrasonic or radiographic testing have been correctly located and are indeed surface breaking.
Penetrant testing, dye penetrant testing or sometimes shortened to dye pen is a method which can be used to find surface breaking defects on nearly all non-porous materials.
A bright dye is applied on the surface of the object and then left for a specified period of time. During this time dye will be drawn in to any surface breaking defects due to a phenomena known as capillary action. After the ‘dwell’ time has elapsed the dye is removed from the surface of the part, with care being taken not to over clean the part. After the part has been suitably prepared a special developer is applied, often a chakly suspension which is sprayed on in a thin coating, leaving a absorbant residue on the part.
The part is now left to ‘develop’. After a specified period to time, the part is inspected and areas where any residual dye has been absorbed by the developer become readily visible revealing flaws in the parts.
Some of the benefits of penetrant testing are:
- A quick and low cost method for finding surface breaking defects.
- Highly portable, to conduct a basic penetrant test only three cans of aerosol consumables are required. Excellent for use in remote locations.
- Unlike MPI, penetrant testing can be used on any non-porous material, including stainless steels, magnesium, aluminium, glass and glazed ceramics.
- Indications found by penetrant testing are by and large fairly easy for the operator to detect and correctly interpret.
Some of the problems associated with using penetrant testing are.
- The penetrant method is only able to find defects that break the surface of the item under test.
- Parts with coatings, galvanising or platings are unsuitable for penetrant testing.
- Processing large parts can be time consuming and labour intensive.
- Post test residual dye can corrode certain metals and alloys and cause other unwanted effects, so parts must be thoroughly cleaned after testing.
- Correct interpretation of indications is down to operator skill and experience. As always, this risk can be greatly reduced by making sure high quality procedures and instructions are in place prior to testing.
Typical uses of penetrant testing are:
Visual Testing (VT)
- Detection of hot tears, cold shuts, gas, porosity and inclusions in castings, especially in non-ferrous castings or with castings with geometry that makes MPI inspection difficult.
- Finding defective areas of weld in fabrications made from stainless steel, aluminium and other non-ferrous materials.
- Looking for tears, cold shuts or porosity in white metal bearing linings.
- Finding cracks and laps in austenitic stainless steel forgings..
- Checking for surface defects on composite welds. For example, lack of fusion defects in Inconel weld overlay sections on stainless steel parts.