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Guide to understanding (WPS), (PQR), (WPQR)

Introduction
Welding requires skill. Determining “how to weld” requires knowledge regarding the materialsbeing welded and welding process, among numerous other factors. Because of huge numberof variables involved, the knowledge of the welding engineer and the skill of the welder needto be validated by a series of tests. All this information is documented on Welding ProcedureSpecification (WPS), Procedure Qualification Record (PQR), Welding ProcedureQualification Record (WPQR), and associated Test Reports.What is Welding Procedure Specification (WPS)? A WPS is a document that describes how welding is to be carried out in production. Itspurpose is to aid the planning and quality control of the welding operation. They arerecommended for all welding operations and most application codes and standards makethem mandatory.What is Procedure Qualification Record (PQR)? A PQR is required when it is necessary to demonstrate that your company has the ability toproduce welds possessing the correct mechanical and metallurgical properties. A welding procedure must be qualified in accordance with the requirements of an appropriatewelding procedure standard, such as ASME Sec IX, as follows:1. Produce a welding procedure specification (WPS) as stated above.2. Weld a test piece in accordance with the requirements of your specification. The jointset up, welding and visual examination of the completed weld should be witnessed bya certified welding inspector such as an AWS certified CWI or an Inspection Body.The details of the test such as the welding current, pre-heat etc., must be recordedduring the test.3. Once the welding is complete the test piece must be subject to destructive and nondestructive examination such as radiography and mechanical tests as defined by thewelding procedure standard. This work must be carried out in a qualified laboratorybut the Inspection Body may require witnessing the tests and viewing anyradiographs.4. If the test is successful you or the test body completes the appropriate documentswhich the test body’s surveyor signs and endorses.

What information should they include?
Sufficient details to enable any competent person to apply the information and produce a

weld of acceptable quality. The amount of detail and level of controls specified on a WPS is
dependant on the application and criticality of the joint to be welded.
For most applications the information required is generally similar to that recorded on a
Procedure Qualification Record (PQR), except that ranges are usually permitted on
thicknesses, diameters, welding current, materials, joint types etc.
If a WPS is used in conjunction with an approved procedure qualification record (PQR) then
the ranges stated should be in accordance with the approval ranges permitted by the PQR.
However careful consideration should be given to the ranges specified to ensure they are
achievable, so that these ranges represent good welding practice.
What is a Prequalified WPS?
Some codes, such as AWS D1.1, allow “Prequalified WPS”, whereby it is established that the
WPS written per code will produce welds with correct mechanical and metallurgical
properties. It is not necessary to prepare a PQR in such cases. However, the pre-qualified
WPS have a specified range of parameters under which the weld must be produced. When
welding variables fall outside these ranges, a WPS with supporting PQR must be prepared.
What are SWPSs?
In an effort to standardize and harmonize the process of WPS approvals, AWS started
writing “Standard Welding Procedure Specifications (SWPSs)” with input from the pioneers
and experts in the welding industry. An extensive testing program was undertaken whereby;
these SWPSs were then supported by numerous PQRs.
When the use of SWPSs is permitted by referencing code section, your company does not
have to perform one or more procedure qualification tests. You can simply purchase the
applicable SWPS for unlimited intra-company use from the American Welding Society
(www.aws.org).

What is Welder Performance Qualification Record (WPQR)?
Once the procedure is approved it is necessary to demonstrate that all your welders working to it have the required knowledge and skill to put down a clean sound weld. If the welder has satisfactorily completed the procedure test then he is automatically approved but each additional welder must be approved by completing an approval test to an appropriate standard such as ASME Sec IX as follows:

1.Complete a weld test as stated above. The test should simulate production conditions and the welding position should be the position that the production welds are to be made in or one more severe.
2. For maximum positional approval a pipe inclined at 45 degrees (referred to as the 6G position) approves all positions except vertical down.
3.Test the completed weld in accordance with the relevant standard to ensure that the weld is clean and fully fused.
4. For a butt weld this is normally a visual examination followed by radiography or bend tests.
5.Once the test is completed the necessary forms have to be completed by you or the test body and signed by the test body’s surveyor.
6. Note that any changes that require a new welding procedure (WPS) may also apply to the welders approval, refer to the referencing code/ standard for precise details
Acceptance Standards
In general welds must show a neat workman like appearance. The root must be fully fused along the entire length of the weld, the profile of the cap should blend in smoothly with the parent material and the weld should be significantly free from imperfections. Reference should be made to the acceptance standard for precise details.
Documentation
The necessary documents for a successful Welding Program are as follows:
1.Welding Procedure Specification (WPS), Procedure Qualification Record (PQR), Independent Laboratory Test Report for the PQR, Welder Performance Qualification Record (WPQR), and Independent Laboratory Test Report for the WPQR; OR
2.Pre-qualified Welding Procedure Specification (Applicable to some Codes only), Welder Performance Qualification Record (WPQR), and Independent Laboratory Test Report for the WPQR; OR

3.Code adopted Standard Welding Procedure Specification (SWPS), Welder Performance Qualification Record (WPQR), and Independent Laboratory Test Report for the WPQR

 

PQR/ WPQR Testing
The following tests by Independent Test Laboratory may be required on your PQR and WPQR Coupons:

Weld Visual Examination by a AWS Certified Welding Inspector
Bend Test
Hardness Test
Transverse Tensile Test
All Weld Metal Tensile Test
Charpy Impact Test
Weld Metal Chemical Analysis
 Macroetch Test
 Torque Test
Peel Test
Nick Break Test
Radiography Test
 Ultrasonic Test

Weld Inspection and Testing
In addition to the above, you may require independent inspection of the welds by the following qualified personnel:
 Visual Inspection by AWS Certified Welding Inspector (CWI)
Radiographic Testing by Level II personnel certified as per SNT-TC-1A
Ultrasonic Testing by Level II personnel certified as per SNT-TC-1A
Magnetic Particle Testing by Level II personnel certified as per SNT-TC-1A
Penetrant Testing by Level II personnel certified as per SNT-TC-1A
AEIS can perform the above tests at your facility or at our laboratory.

Radiographic and Ultrasonic Testing of Welds

Radiographic and ultrasonic weld inspection are the two most common methods of non-destructive testing (NDT) used to detect discontinuities within the internal structure of welds. The obvious advantage of both these methods of testing is their ability to help establish the weld’s internal integrity without destroying the welded component. We shall briefly examine these two methods of non-destructive testing (NDT). We shall consider how they are used and what types of welding discontinuities they can be expected to find. We shall examine their advantages over other inspection methods and their limitations.

Radiographic Testing (RT) – This method of weld testing makes use of X-rays, produced by an X-ray tube, or gamma rays, produced by a radioactive isotope. The basic principle of radiographic inspection of welds is the same as that for medical radiography. Penetrating radiation is passed through a solid object, in this case a weld rather that part of the human body, onto a photographic film, resulting in an image of the object’s internal structure being deposited on the film. The amount of energy absorbed by the object depends on its thickness and density. Energy not absorbed by the object will cause exposure of the radiographic film. These areas will be dark when the film is developed. Areas of the film exposed to less energy remain lighter. Therefore, areas of the object where the thickness has been changed by discontinuities, such as porosity or cracks, will appear as dark outlines on the film. Inclusions of low density, such as slag, will appear as dark areas on the film while inclusions of high density, such as tungsten, will appear as light areas. All discontinuities are detected by viewing shape and variation in density of the processed film.

Radiographic testing can provide a permanent film record of weld quality that is relatively easy to interpret by trained personnel. This testing method is usually suited to having access to both sides of the welded joint (with the exception of double wall signal image techniques used on some pipe work). Although this is a slow and expensive method of nondestructive testing, it is a positive method for detecting porosity, inclusions, cracks, and voids in the interior of welds. It is essential that qualified personnel conduct radiographic interpretation since false interpretation of radiographs can be expensive and interfere seriously with productivity. There are obvious safety considerations when conducting radiographic testing. X-ray and gamma radiation is invisible to the naked eye and can have serious heath and safety implications. Only suitably trained and qualified personnel should practice this type of testing.

Ultrasonic Testing (UT) – This method of testing makes use of mechanical vibrations similar to sound waves but of higher frequency. A beam of ultrasonic energy is directed into the object to be tested. This beam travels through the object with insignificant loss, except when it is intercepted and reflected by a discontinuity. The ultrasonic contact pulse reflection technique is used. This system uses a transducer that changes electrical energy into mechanical energy. The transducer is excited by a high-frequency voltage, which causes a crystal to vibrate mechanically. The crystal probe becomes the source of ultrasonic mechanical vibration. These vibrations are transmitted into the test piece through a coupling fluid, usually a film of oil, called a couplant. When the pulse of ultrasonic waves strikes a discontinuity in the test piece, it is reflected back to its point of origin. Thus the energy returns to the transducer. The transducer now serves as a receiver for the reflected energy. The initial signal or main bang, the returned echoes from the discontinuities, and the echo of the rear surface of the test piece are all displayed by a trace on the screen of a cathode-ray oscilloscope. The detection, location, and evaluation of discontinuities become possible because the velocity of sound through a given material is nearly constant, making distance measurement possible, and the relative amplitude of a reflected pulse is more or less proportional to the size of the reflector.

One of the most useful characteristics of ultrasonic testing is its ability to determine the exact position of a discontinuity in a weld. This testing method requires a high level of operator training and competence and is dependant on the establishment and application of suitable testing procedures. This testing method can be used on ferrous and nonferrous materials, is often suited for testing thicker sections accessible from one side only, and can often detect finer lines or plainer defects which may not be as readily detected by radiographic testing.

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