Induction Heat Treatment
The importance of fast, accurate and uniform heating as part of the pipeline welding specification has grown significantly. This has resulted from the increased use of heavy wall pipe and modern automatic and semi-automatic welding systems.
Traditional gas flame and resistance heating systems are often impractical where higher temperatures are specified. They are not only too slow to meet the cycle times demanded by the industry, but also the heating is too inaccurate and lacks uniformity around the full circumference and bandwidth of the weld joint.
The benefits of the induction heating system are:
- Much faster temperature rise than gas or resistance heating
- Variable control over temperature/time parameters
- Accurate, uniform heating over a controlled bandwidth and around the full pipe circumference
- Fast, accurate, reliable and cost-effective
- Minimal damage (if any) to factory coating
- Designed with the lay contractor in mind
- Equipment is robust and reliable
- Simple, lightweight, user-friendly equipment operation
- Induction heat is 'direct into metal'
- No deleterious surface residues are produced
- No naked flames or exposed elements
- Heat is localised
- Temperature measurements stay within specification
- Does away with the need to set aside a large storage area for gas
- Unlike gas heating, the induction system is not impaired by very low ambient temperatures
Pipeline Induction Heat's pre-weld induction heating systems have been designed for both onshore and offshore field operation, at mainline / front end or double jointing locations. Originally engineered for use on large diameter heavy wall pipes, in association with automatic welding systems, induction pre-heat is equally useful where manual stick-welding is being employed during cold weather conditions.
In certain circumstances, particularly for offshore fast production pipe lay using automatic welding systems, unexpected delays can disrupt the welding process on the lay barge firing-line.
These 'hold-ups' can lead to degradation of the partially welded joint, which may require further filling before it is fully completed. To prevent degradation and embrittlement of the weld, which could lead to a negative NDT / X-ray result down line, PIH have designed a re-heat induction heating system. This consists of a hinged coil designed to pass heat into the localised area of the weld margin only.
As an integral part of many modern pipeline welding specifications Interpass Heating is performed at a number of welding stations, in order to prevent stresses building up in the weld metal, which would otherwise necessitate a post-weld stress relieving (annealing) cycle.
For offshore operations, hinged Interpass/Re-Heat induction heating coils are suspended by air hoists from a monorail which runs overhead to the welding stations, either at the mainline or double joint areas. When required, the coil can be rapidly located around the partly welded field joint. The coil is immediately energised and the joint temperature boosted to a level which complies with the welding specification, thus overcoming any hardness or minimum heat requirements at the next welding station.
Our Interpass/Re-Heat systems are generally offered as an 'extra', when a client selects to utilise PIH induction pre-heat systems.
Post Weld Heat Treatment
PIH's post-weld induction heating system is intended for lay barge operation, for diameters ranging from 6" to 72", with no limit on wall thickness. Temperature ranges are typically 0 to 650°C.
The purpose of induction post-heating is to provide a rapid, accurate heating cycle, to stress-relieve (anneal) a recently welded pipe joint. This is typically required following specialist automatic welding of very heavy wall pipe, which can result in embrittlement of the weld metal, leading to unacceptable 'hardness values'. To overcome this problem, the weld area must be subjected to a pre-calculated heat treatment programme, within the fast laybarge welding production cycle.