Tuesday, December 2, 2008


There are many types of work which require engineering materials to be joined by welding, for example:

Pressure vessels
Oil rigs
Earth moving equipment
Ventilation systems
Storage tanks
Heavy vehicle chassis
Car bodies
Food processing plant

The quality requirements of the joints in these fabrications depend on their fitness-for-purpose and differ significantly from one application to the next. Pressure vessels require welds, which can withstand the stresses and high temperatures experienced in operation. Oilrigs are designed to withstand the effect of wave formation and wind loads. Earth moving equipment has to accommodate differences in terrain and earth conditions and is subject to fatigue loading. Welds in food processing plants must withstand corrosion by hot acidic liquors.
Below are listed some typical codes of practice and standards which cover various types of constructions fabricated by welding.

Code----------- Class of Work
BS 5500-------- Unfired fusion welded pressure vessels
ASME VIII------ American boiler and pressure vessel code
BS 2633-------- Class 1 arc welding of ferritic steel pipe work for carrying fluids
BS 4515-------- Process of welding steel pipelines on land and offshore
BS 5950-------- Structural use of steelwork in building
AWS D1.1------- Structural welding code (American)
BS 5400-------- Steel, concrete and composite bridges
BS 6235-------- Code of practice for fixed offshore structure
API 1104------- Standard for welding pipelines and related structures

These documents can also provide a useful source of data for applications where codes do not exist. It should be remembered, however, that the principal criterion in the codes listed is the quality of the joint in relation to the service conditions. There are other applications where success is judged by different criteria, such as dimensional accuracy.
Another important consideration is controlling the cost of welding. Variations in weld times and quantities of consumables can readily result if the method of making a weld is left to the welder to decide.
The continuous and satisfactory performance of weldments made to various codes requires that specific guidelines are laid down to cover all variables. These guidelines are usually grouped under the general heading of a Weld Procedure.


A code of practice is a set of rules for manufacturing a specific product. It should contain:
Design Requirements (e.g. fit-up, preparation and type of joints)
Material (e.g. types, thickness ranges)

Manufacturer’s Working Practice
Inspection Criteria (e.g. 100% visual, percentage other NDT)
Acceptance Criteria (e.g. defect size, limits, etc.)
Welding Process (e.g. type, consumables)
Types Of Tooling (e.g. use of strongbacks)

Contractual Information
The difference between a code and a standard is that a code states how to do a specific job and does not contain all relevant information, but refers to other standards for details.
A code or standard generally mentions three parties - the customer or client, the manufacturer or producer and the inspection authority. In a code the term ‘shall’ means mandatory - must be done, and the term ‘should’ means recommended - not compulsory.
A concession is an agreement between the contracting parties to deviate from the original code requirements. (BS 5135)


At any point in the course of welding, i.e. tacking, root pass, filler pass or capping pass, but particularly for the root and cap, a detailed inspection may be required. British Standard 5289: 1976 gives guidance on tools and responsibilities together with sketches of typical defects.

The inspector at this point must -
a)observe, identify and perhaps record (measure) the features of the weld.
b)decide whether the weld is acceptable in terms of the particular levels that are permitted; defect levels may be ‘in-house’ or national codes of practice.

When the defect size is in excess of the permitted level then either a concession must be applied for (from a competent person), or the weld rejected.

Illumination:Good lighting is essential.
Inspection Lenses: The magnification should not exceed 2 - 2.5 diameters. If higher magnification is required use a binocular microscope.Optical viewing can progressively develop from eyesight, to use of a hand torch and mirror, to the addition of a magnifier and light source.

In order to achieve accessibility, remote probe units are available which must have the following properties.
a)Large field of vision
b)Freedom from distortion of image
c)Accurate preservation of colour values
d)Adequacy of illumination

A code of practice for an inspection department should take the form outlined below. It is appreciated that full implementation of the code would be extremely costly and therefore it may be necessary to reduce the amount of inspection to less than is theoretically required.

The inspector should be familiar with the following:
a)All applicable documents
b)Workmanship standards
c)All phases of good workshop practice
d)Tools and measuring devices

Before Assembly:
Check * All applicable documents.
* Quality plan is authorised and endorsed with signature, date and company stamp.
* Application standard is up to date with the latest edition, revision or amendment.
* The drawings are clear, the issue number is marked and the latest revision is used.
* Welding procedure sheets (specifications) are available, have been approved and are employed in production.
* Welder qualifications with identification and range of approval are verified and that only approved welders as required are employed in production.
* Calibration certificates, material certificates (mill sheets) and consumer certificates are available and valid.
* Parent material identification is verified against documentation and markings.
* Material composition, type and condition.
* Correct methods are applied for cutting and machining.
* Identification of welding consumables such as electrodes, filler wire, fluxes, shielding and backing gases and any special requirements (e.g. drying) are met.
* Plant and equipment are in a safe condition and adequate for the job.
* Safety permits e.g. hot work permit, gas free permit, enclosed space certificate are available and valid.

After Assembly
Check * Dimensions, tolerances, preparation, fit-up and alignment are in accordance with the Approved drawings and standards.
* Tack welds, bridging pieces, clamping and type of backing - if any used are correct.
* Cleanliness of work area is maintained.
* Preheat in accordance with procedure.

NOTE Good inspection prior to welding can eliminate conditions that lead to the formation of defects.

Check * The welding process must be monitored.
* Preheat and interpass temperatures must be monitored.
* Interpass cleaning - chipping, grinding, gouging, must be monitored.
* Root and subsequent run sequence.
* Essential variables such as current, voltage, travel speed to be monitored.
* Filler metals, fluxes and shielding gases are correct.
* Welding is in compliance with weld procedure sheet and application standard.

Check * Visual inspection to be carried out to ascertain acceptability of appearance of welds.
* Dimensional accuracy to be ascertained.
* Conformity with drawings and standards requirements.
* Post weld heat treatment, if any, monitored and recorded.
* NDT carried out and reports assessed.
* Assess defects as to either repairing, or application for concession.
* Carry out any necessary repairs.
* Control of distortion
* Repair procedure and welding code should be authorised.
* Defect area should be marked positively and clearly.
* Check when partially removed and fully removed (visual and NDT).
* Re-welding should be monitored.
* Re-inspect completed repair.

Collate all documents and reports. Pass the document package on to a higher authority for final inspection, approval and storage.


Ensure compliance with standard or code.
Ensure workmanship.
Ensure welding criteria by ‘policing’ work and documentation.

Honesty and integrity.
Fitness - physical and eyesight.


Welder’s Test Position (ASME IX QW-461.3-461.7)

Groove Welds in Plate - Test Positions
1G, 2G, 3G & 4G

Groove Welds in Pipe - Test Positions
1G (rotated), 2G, 5G, 6G

Fillet Welds in Plate - Test Positions
1F, 2F, 3F, 4F

Fillet Welds in Pipe- Test Positions
1F (rotated), 2F, 2FR (rotated), 4F & 5F

Stud Welds - Test Positions
1S, 2S & 4S