Dye penetrant inspection:

• Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or Penetrant Testing  (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non – porus materials (metals, plastics, or ceramics).
• The penetrant may be applied to all non-ferrous materials and ferrous materials, although for ferrous components magnetic particle inspection is often used instead for its subsurface detection capability.
• LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.

Principles:

• Dye penetrant inspection (DPI)  is based upon capillary action, where low surface tension fluid penetrates into clean and dry surface-breaking discontinuities.
• Penetrant may be applied to the test component by dipping, spraying, or brushing.
• After adequate penetration time has been allowed, the excess penetrant is removed and a developer is applied.
• The developer helps to draw penetrant out of the flaw so that an invisible indication becomes visible to the inspector.
• Inspection is performed under ultraviolet or white light, depending on the type of dye used – flurescent or nonfluorescent (visible).

Inspection Steps:

Below are the main steps of Dye penetrant inspection (DPI), liquid penetrant inspection (LPI) or Penetrant Testing  (PT):

1. Pre-cleaning:

• The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting.
• The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination.
• Note that if media blasting is used, it may “work over” small discontinuities in the part, and an etching bath is recommended as a post-blasting treatment.

2. Application of Penetrant:

• The penetrant is then applied to the surface of the item being tested.
• The penetrant is allowed “dwell time” to soak into any flaws (generally 5 to 30 minutes).
• The dwell time mainly depends upon the penetrant being used, material being tested and the size of flaws sought.
• As expected, smaller flaws require a longer penetration time.
• Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant.

3. Excess Penetrant Removal:

• The excess penetrant is then removed from the surface.
• The removal method is controlled by the type of penetrant used.
• Water-washable, solvent-removable, Liphopilic post-emulsifiable, or hydrophilic  post-emulsifiable are the common choices.
• Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a water spray.
• When using solvent remover and lint-free cloth it is important to not spray the solvent on the test surface directly, because this can remove the penetrant from the flaws.
• If excess penetrant is not properly removed, once the developer is applied, it may leave a background in the developed area that can mask indications or defects.
• In addition, this may also produce false indications severely hindering your ability to do a proper inspection.
• Also, the removal of excessive penetrant is done towards one direction either vertically or horizontally as the case may be.

4. Application of Developer:

• After excess penetrant has been removed, a white developer is applied to the sample.
• Several developer types are available, including:non- aqueous wet developer, dry powder, water-suspendable, and water-soluble.
• Choice of developer is governed by penetrant compatibility (one can’t use water-soluble or -suspendable developer with water-washable penetrant), and by inspection conditions.
• When using non-aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while soluble and suspendable developers are applied with the part still wet from the previous step.
• NAWD is commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a propellant that is a combination of the two. Developer should form a semi-transparent, even coating on the surface.
• The developer draws penetrant from defects out onto the surface to form a visible indication, commonly known as bleed-out. Any areas that bleed out can indicate the location, orientation and possible types of defects on the surface.
• Interpreting the results and characterizing defects from the indications found may require some training and/or experience [the indication size is not the actual size of the defect].

5. Inspection:

• The inspector will use visible light with adequate intensity (100 foot-candles or 1100 lux is typical) for visible dye penetrant.
• Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimeter squared is common), along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations.
• Inspection of the test surface should take place after 10- to 30-minute development time, depends of product kind.
• This time delay allows the blotting action to occur.
• The inspector may observe the sample for indication formation when using visible dye.
• It is also good practice to observe indications as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws.

6. Post Cleaning:

• The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are scheduled.

Dye penetrant inspection (DPI)

Advantages and Disadvantages:

• The main advantages of Dye penetrant inspection (DPI), are the speed of the test and the low cost.
• Disadvantages include the detection of only surface flaws, skin irritation, and the inspection should be on a smooth clean surface where excessive penetrant can be removed prior to being developed.
• Conducting the test on rough surfaces, such-as “as-welded” welds, will make it difficult to remove any excessive penetrant and could result in false indications.
• Water-washable penetrant should be considered here if no other option is available. Also, on certain surfaces a great enough color contrast cannot be achieved or the dye will stain the workpiece.
• Limited training is required for the operator — although experience is quite valuable. Proper cleaning is necessary to assure that surface contaminants have been removed and any defects present are clean and dry. Some cleaning methods have been shown to be detrimental to test sensitivity, so acid etching to remove metal smearing and re-open the defect may be necessary.

API 510 Pressure Vessel Inspector

API 510 Pressure Vessel Inspector

Chapter 1

Interpreting ASME and API Codes Passing the API ICP examination is, unfortunately, all about interpreting codes. As with any other written form of words, codes are open to interpretation. To complicate the issue, different forms of interpretation exist between code types; API and ASME are separate organizations so their codes are structured differently, and written in quite different styles.

1.1 Codes and the real world

Both API and ASME codes are meant to apply to the real world, but in significantly different ways. The difficulty comes when, in using these codes in the context of the API ICP examinations, it is necessary to distil both approaches down to a single style of ICP examination question (always of multiple choice, single-answer format).

1.2 ASME construction codes

ASME construction codes (VIII, V and IX) represent the art of the possible, rather than the ultimate in fitness for service (FFS) criteria or technical perfection. They share the common feature that they are written entirely from a new construction viewpoint and hence are relevant up to the point of handover or putting into use of a piece of equipment. Strictly, they are not written with in-service inspection or repair in mind. This linking with the restricted activity of new construction means that these codes can be prescriptive, sharp-edged and in most cases fairly definitive about the technical requirements that they set. It is difficult to agree that their content is not black and white, even if you do not
agree with the technical requirements or acceptance criteria, etc., that they impose. Do not make the mistake of confusing the definitive
requirements of construction codes as being the formal arbiter of FFS. It is technically possible, in fact common-place, to use an item safely that is outside code requirements as long as its integrity is demonstrated by a recognized FFS assessment method.

1.3 API inspection codes

API inspection codes (e.g. API 510 Pressure Vessel Inspector) and their supporting recommended practice documents (e.g. API RP 572 and 576) are very different. They are not construction codes and so do not share the prescriptive and ‘black and white’ approach of construction codes. There are three reasons for this:
. They are based around accumulated expertise from a wide variety of equipment applications and situations.
. The technical areas that they address (corrosion, equipment lifetimes, etc.) can be diverse and uncertain.
. They deal with technical opinion, as well as fact.

Taken together, these make for technical documents that are more of a technical way of looking at the world than a solution, unique or otherwise, to a technical problem. In such a situation you can expect opinion to predominate.
Like other trade associations and institutions, API (and ASME) operate using a structure of technical committees. It is committees that decide the scope of codes, call for content, review submissions and review the pros and cons of what should be included in their content. It follows therefore that the content and flavour of the finalized code documents are the product of committees. The output of committees is no secret – they produce fairly well-informed opinion based on an accumulation of experience, tempered, so as not to appear too opinionated or controversial, by having the technical edges taken off. Within these constraints there is no doubt that API 510 Pressure Vessel Inspector API codes do provide sound and fairly balanced technical opinion. Do not be surprised, however, if this opinion does not necessarily match your own.

1.3.1 Terminology

API and ASME documents use terminology that occasionally differs from that used in European and other codes. Non-destructive examination (NDE), for example, is normally referred to as non-destructive testing (NDT) in Europe and API work on the concept that an operative who
performs NDE is known as the examiner rather than by the term technician used in other countries. Most of the differences are not particularly significant in a technical sense – they just take a little getting used to. In some cases, meanings can differ between ASME and API codes (pressure and leak testing are two examples).API 510 Pressure Vessel Inspector  API codes benefit from their principle of having a separate section (see API 510 section 3) containing definitions. These definitions are selective rather than complete (try and find an accurate explanation of the difference between the terms approve and authorize, for example). Questions from the ICP examination papers are based solely on the terminology and definitions understood by the referenced codes. That is the end of the matter.

1.3.2 Calculations

Historically, both API and ASME codes were based on the United States Customary System (USCS) family of units. There are practical differences between this and the European SI system of units. SI is a consistent system of units, in which equations are expressed using a combination of base units. For example: Stress = pressure X diameter / 2 X  thickness In SI units all the parameters would be stated in their base units, i.e.
Stress: N/m2 (Pa)
Pressure: N/m2 (Pa)
Diameter: m
Thickness: m
Compare this with the USCS system in which parameters may be expressed in several different ‘base’ units, combined with a multiplying factor. For example the equation for determining the minimum allowable corroded shell thickness of storage tanks is:
tmin =  (2.6H –  1)DG/SE
where tmin is in inches, fill height (H) is in feet, tank diameter (D) is in feet, G is specific gravity, S is allowable stress and E is joint efficiency.
Note how, instead of stating dimensions in a single base unit (e.g. inches) the dimensions are stated in the most convenient dimension for measurement, i.e. shell thickness in inches and tank diameter and fill height in feet. Remember that:
. This gives the same answer; the difference is simply in the method of expression.
. In many cases this can be easier to use than the more rigorous SI system – it avoids awkward exponential (106, 106, etc.) factors that have to be written in and subsequently cancelled out.
. The written terms tend to be smaller and more convenient.

1.3.3 Trends in code units

Until fairly recently, ASME and API codes were written exclusively in USCS units. The trend is increasing, however, to develop them to express all units in dual terms USCS(SI), i.e. the USCS term followed by the SI term in brackets. Note the results of this trend:
. Not all codes have been converted at once; there is an inevitable process of progressive change.
. ASME and API, being different organizations, will inevitably introduce their changes at different rates, as their codes are revised and updated to their own schedules.
. Unit conversions bring with them the problem of rounding errors. The USCS system, unlike the SI system, has never adapted well to a consistent system of rounding (e.g. to one, two or three significant figures) so errors do creep in.
The results of all these is a small but significant effect on the form of examination questions used in the ICP examination and a few more opportunities for errors of expression, calculation and rounding to creep in. On balance, ICP examination questions seem to respond better to being treated using pure USCS units (for which they were intended). They do not respond particularly well to SI units, which can cause problems with conversion factors and rounding errors.

1.4 Code revisions

Both API and ASME review and amend their codes on a regular basis. There are various differences in their approach but the basic idea is that a code undergoes several addenda additions to the existing edition, before being reissued as a new edition. Timescales vary – some change regularly and others hardly at all. Owing to the complexity of the interlinking and crossreferencing between codes (particularly referencing from API to ASME codes) occasional mismatches may exist temporarily. Mismatches are usually minor and unlikely to cause any problems in interpreting the codes. It is rare that code revisions are very dramatic; think of them more as a general process of updating and correction. On occasion, fundamental changes are made to material allowable stresses (specified in ASME II-D), as a result of experience with material test results, failures or advances in manufacturing processes.

1.5 Code illustrations

The philosophy on figures and illustrations differs significantly between ASME and API codes as follows:
. ASME codes (e.g. ASME VIII), being construction-based,contain numerous engineering-drawing style figures and
tables. Their content is designed to be precise, leading to clear engineering interpretation.
. API codes are not heavily illustrated, relying more on text. Both API 510 Pressure Vessel Inspector and its partner pipework inspection code, API 570, contain only a handful of illustrations between them.
. API Recommended Practice (RP) documents are better illustrated than their associated API codes but tend to be less formal and rigorous in their approach. This makes sense, as they are intended to be used as technical information documents rather than strict codes, as such. API RP 572 is a typical example containing photographs, tables and drawings (sketch format) of a fairly general nature. In some cases this can actually make RP documents more practically useful than codes.

1.6 New construction versus repair activity
This is one of the more difficult areas to understand when dealing with ASME and API codes. The difficulty comes from the fact that, although ASME VIII was written exclusively from the viewpoint of new construction, it is referred to by API 510 Pressure Vessel Inspector  in the context of in-service repair and,to a lesser extent, re-rating. The ground rules (set by API) to manage this potential contradiction are as follows (see Fig 1.1).
. For new construction, ASME VIII is used – and API 510 Pressure Vessel Inspector plays no part.
. For repair, API 510 Pressure Vessel Inspector is the ‘driving’ code. In areas where it references ‘the construction codes’ (e.g. ASME VIII), this is followed when it can be (because API 510 Pressure Vessel Inspector has no content that contradicts it).
. For repair activities where API 510 Pressure Vessel Inspector and ASME VIII contradict, then API 510 Pressure Vessel Inspector takes priority. Remember that these contradictions are to some extent false – they only exist because API 510 Pressure Vessel Inspector is dealing with on-site repairs, while

 

 

 

 

 

 

 

 

 

 

 

ASME VIII was not written with that in mind. API 510 Pressure Vessel Inspector Two areas where this is an issue are:
. some types of repair weld specification (material, fillet size, electrode size, etc.);
. how and when vessels are pressure tested.

1.7 Conclusion:

interpreting API and ASME codes In summary, then, the API and ASME set of codes are a fairly comprehensive technical resource, with direct application to plant and equipment used in the petroleum industry. They are perhaps far from perfect but, in reality, are much more comprehensive and technically consistent than manyothers. Most national trade associations and institutions do not have any in-service inspection codes at all, so industry has to rely on a fragmented collection from overseas sources or nothing at all. The API ICP scheme relies on these ASME and API 510 Pressure Vessel Inspector API codes for its selection of subject matter (the so-called ‘body of knowledge’), multiple exam questions and their answers. One of the difficulties is shoe-horning the different approach and style of the ASME codes (V,VIII and IX) into the same style of questions and answers that fall out of the relevant API documents (in the case of the API 510 Pressure Vessel Inspector ICP these are API 571/572/576/577). Figure 1.2 shows the situations. It reads differently, of course, depending on whether you are looking for reasons for difference or seeking some justification for
similarity. You can see the effect of this in the style of many of the examination questions and their ‘correct’ answers. Difficulties apart, there is no question that the API 510 Pressure Vessel Inspector API ICP examinations are all about understanding and interpreting the relevant ASME and API codes. Remember, again, that while these codes are based on engineering experience, do not expect that this experience necessarily has to coincide with your own. Accumulated experience is incredibly wide and complex, and yours is only a small part of it.

Non Destructive Testing

 

Non Destructive Testing  is the use of noninvasive techniques to determine the integrity of a material, component or structure or quantitatively measure some characteristics of an object. It is the testing of materials, for surface or internal flaws or metallurgical condition, without interfering in any way with the integrity of the material or its suitability for service.

i.e. Inspect or measure without doing harm.

Importance of Non Destructive Testing (NDT)

1.Non Destructive Testing (NDT) increases the safety and reliability of the product during operation.

2.It decreases the cost of the product by reducing scrap and conserving materials, labor and energy.

3.It enhances the reputation of the manufacturer as a  producer of quality goods. All of the above factors boost the sales of the product which bring more economical benefits for the manufacturer.

4.Non Destructive Testing (NDT) is also used widely for routine or periodic determination of quality of the plants and structures during service.

5.This not only increases the safety of operation but also eliminates any forced shut down of the plants.

Six Most Common Non Destructive Testing (NDT) Methods:

1. Visual Testing (VT)
2. Dye Penetrant Testing (DPT)
3. Magnetic Particle Testing (MPT)
4. Ultrasonic Testing (UT)
5. Eddy Current Testing (ECT)
6. Radiography Testing (RT)

Visual testing is the most basic and common inspection method involves in using of human eyes to look for defects. But now it is done by the use special tools such as video scopes, magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area.

Visual Testing Equipments:

• Mirrors (especially small, angled mirrors),
• Magnifying glasses,
• Microscopes (optical and electron),
• Borescopes and fiber optic borescopes,
• Closed circuit television (CCTV) systems,
• Videoscope.

Visual Testing Equipments

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dye Penetrant Testing

This method is commonly used for detect the surface cracks or defects. Dye penetrant Testing (DPT) is one of the most widely used Non Destructive Testing (NDT) methods. DPT can be used to inspect almost any material provided that its surface is not extremely rough.

Dye Penetrant Testing Process

Three liquids are used in this method.

1.Cleaner

2.Penetrant

3.Developer

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dye Penetrant Testing of a Boiler

 

 

 

 

 

 

 

 

 

 

 

 

 

At first the surface of the material that is to be tested is cleaned by a liquid. The liquid is called cleaner.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Then a liquid with high surface wetting characteristics is applied to the surface of the part and allowed time to seep into surface breaking defects. This liquid is called penetrant. After five or ten minutes the excess penetrant is removed from the surface.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Then another liquid is applied to pull the trapped penetrant out the defect and spread it on the surface where it can be seen. This liquid is called deveoper.

Findings

After Dye Penetrant Testing there are two surface cracks are Detected.

 

 

 

 

 

 

 

 

 

 

 

 

Advantages of Dye Penetrant  Testing

• This method has high sensitivity to small surface discontinuities.
• Large areas and large volumes of parts/materials can be inspected rapidly and at low cost.
• Indications are produced directly on the surface of the part and constitute a visual representation of the flaw.
• Aerosol spray can make penetrant materials very portable.
• Penetrant materials and associated equipments are relatively inexpensive.

Limitations of Dye Penetrant  Testing

• Only surface breaking defects can be detected.
• Precleaning is critical since contaminants can mask defects.
• The inspector must have direct access to the surface being inspected.
• Surface finish and roughness can affect inspection sensitivity.
• Post cleaning of acceptable parts or materials is required.
• Chemical handling and proper disposal is required.

Magnetic Particle Testing

This method is suitable for the detection of surface and near surface discontinuities in magnetic material, mainly ferrite steel and iron. Magnetic particle Testing (MPT) is a nondestructive testing method used for defect detection. MPT is fast and relatively easy to apply, and material surface preparation is not as critical as it is for some other Non-Destructive Testing (NDT) methods.

 

 

 

 

 

 

 

 

 

 

 

 

Basic Principle of MPT

 

 

 

 

 

 

In the first figure the magnetized metal has no crack and there only two poles that is north pole and south pole. And in second figure the magnetized metal has a crack and at the crack point there creates another north and south pole for the magnetic flux leakage.

Magnetic Particle Testing Process

The first step in a magnetic particle testing is to magnetize the  test component by a MPT equipment. If there any defects on the surface or near to the surface are present, the defects will create a leakage field.

Then finely milled iron particles coated with a dye pigment are applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the defects. This indication can be visually detected under proper lighting conditions.

 

 

 

 

 

 

 

 

Magnetic Particle Testing in Superheater Pipe Welding

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

First the welding joint is magnetized by MPT equipment. Then finely milled iron particles are applied to the magnetized weld joint.

Magnetic Particle Testing in Gas Pipe Welding:

Iron particles make a cluster at the welding joint for magnetic flux leakage because of welding defects.

Advantages Magnetic Particle Testing:

• It does not need very stringent pre-cleaning operation.
• It is the best method for the detection of surface and near to the surface cracks in ferromagnetic materials.
• Fast and relatively simple Non Destructive Testing (NDT)  method.
• Generally inexpensive.
• Will work through thin coating.
• Highly portable NDT method.
• It is quicker.

Limitations of Magnetic Particle Testing:

• Material must be ferromagnetic.
• Orientation and strength of magnetic field is critical.
• Detects surface and near-to-surface discontinuities only.
• Large currents sometimes require.

Ultrasonic Testing

This technique is used for the detection of internal surface (particularly distant surface) defects in sound conducting materials. In this method high frequency sound waves are introduced into a material and they are reflected back from surface and flaws. Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features.

 

 

 

 

 

 

 

 

Basic Principle of Ultrasonic Testing

A typical UT system consists of several functional units, such as the pulser/receiver, piezoelectric transducer, and display devices. A pulser/receiver is an electronic device that can produce high voltage electrical pulses. Driven by the pulser, the transducer generates high frequency ultrasonic energy. The sound energy is introduced and propagates through the materials in the form of waves. When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected back from the flaw surface. The reflected wave signal is transformed into an electrical signal by the piezoelectrical transducer and is displayed on a screen.

In the figure below, the reflected signal strength is displayed versus the time from signal generation, when a echo was received. Signal travel time can be directly related to the distance. From the signal, information about the reflector location, size, orientation and other features can sometimes be gained.