CODES AND STANDARDS

CODES AND STANDARDS

CLASS OF WORK

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

Pressure vessels Bridges

Oil rigs Earth moving equipment

Aero-engines 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.

CODE OF PRACTICE

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

Materials 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 strong backs

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)