Strengthening structures for recertification WHO have exhausted its design life
Improvement due to design errors
Repairs due to damage Caused by:
Error during installation
Incidents, eg ship-groundings, storms, falling objects from the upper deck, etc.
cracks at the junction due to environmental conditions (waves, wind)
The Addition of the structure Because of changes in operations (riser clamp installation, caisson, etc..)
Anode installation
As Mentioned above That have not been many interested parties to implement these underwater welding techniques. It is evident That there are only 50 events under the water for repair welding of offshore structures were published during That the last 40 years, it's also a bit of information That is technique. The industry is still interested in using hyperbaric welding or mounting clamp even though it took preparation is more complicated and more expensive costs. Below are described some of the obstacles still exist That Make That the industry is still reluctant to use this technique, as well as some challenges if we want to use it. Interventions for the above, there are Several commonly used techniques Such as
Grinding out cracks
- Clamps
- Grout filling
- Hyperbaric welding
- Underwater welding
The reluctance of the industry to use underwater welding technique is understandable considering the Following things:
Class, either DNV or have not received LR technique for permanent repairs. There are weld the which almost always accompanies defects (porosity, lack offusion, cracking) these burdensome welding technique for permanent improvement purposes. element is to repair the 'less important', classs can accept it as a conditional permanent Could be Considered a permanent home in the next inspection found no significant reduction of the quality of welding TSB.
AWS D3.6 refers to: 1999 'Specification for underwater welding', the best results can be obtained from this technique is a new Class B. Such results can only be acceptable if the purpose of welding That is only for the applications are less Important / critical applications where lower ductility, porosity is more, the discontinuities are Relatively more acceptable. If welding is used usually only applied for purposes That are 'fit for purpose' only.
The high risk of hydrogen cracking in the HAZ area, ESPECIALLY for That material has higher levels of carbon equivalent of 0.4%. Especially in the North Sea, offshore structures used to use this material.
Of experience in the industry, welding technique is only performed up into no more than 30 m.
Shielded metal arc process performance (SMA) of ferritic electrodes deteriorate with advancing into.
Commercial producers also limit the use of electrodes to a depth of 100 meters.
The nature of the welding results also deteriorated with Increasing depth, ESPECIALLY for small ductility and toughness.
Due to direct contact with water, the water around the welding area to boil and Becomes ionized hydrogen gas and oxygen. Most of the gas is fused into the HAZ area but most of the others will flow into the water. When the flow is retained, there will be a risk of explosion is usually harmful to divers.
RESOLUTION
Although there are Several obstacles That made the industry reluctant to use this welding technique, there are actually some of the restoration effort has been done That, both in technique and quality of welding electrodes, Such as:
Hydrogen cracking and HAZ hardness in the area can be minimized or avoided by the application of multiple temper bead (MTB). The concept of this technique is to control the ratio of heat (heat input) Between the layers of the welding bead. To control this heat, the size of the weld bead on the first layer should be 'adjusted' so That the minimum penetration into the material Could be obtained. Likewise for the second layer and so on. That there are three parameters affect the quality of welding in the application of this MTB, namely: the distance Between the temper bead, timescales and heat input welding.
Buttering technique can also be used primarily for materials with more than 0.4% CE. Electrodes butter use oxidizing agent electrode or electrodes have Thermit.
Usage of the electrode with the oxidizing agent, this agent will absorb hydrogen or oxygen gas is absorbed in Haz
Use of Thermit used. Electrode electrodes Could also be producing this type of high heat delivery and welding material (weld metal) are thereby slightly reducing the rate of cooling of the welding by the surrounding temperature, Causing a kind of post weld heat treatment process.
Nickel-based electrodes can not withstand the hydrogen to diffuse into HAZ area. unfortunately only a hardness in the HAZ area is still high and the welding quality is only good for up to 10 meters depth.
WE MUST DO
As Mentioned above, in Addition to lower cost, the most Important thing to Consider in the selection of underwater welding applications is the preparation of the brief. Equipment used for this work is similar to dry welding techniques. there are some Things to think about so That the application of underwater wet welding technique is more acceptable to the industry:
The Things Mentioned above to bridge shortcomings in the new underwater welding job proved to a depth of up to 30 meters. Welding institutions must be proactive to try new techniques for deeper waters.
Welding techniques depend on the ability of divers. That means even if the technique allows, welding can only be done up to a depth of 200 meters. Needs to Consider the use of automatic or mechanical techniques for deeper waters.
