Jun-2008

Managing construction projects using welding coordinator software

This article describes the construction of LNG facilities by CB&I and how the Welding Coordinator software developed by TWI helped CB&I manage the construction of the LNG facilities at Grain, Kent

Andre Dorset, CB&I
Andy Brightmore, TWI Ltd

Article Summary

LNG, Natural gas is a vital component of the world’s supply of energy. It is one of the cleanest, safest and most useful of all energy sources. Some 24% of energy consumed in the US in 2000 was generated from natural gas and it is used to heat homes, power industry and generate electricity.1 However, transporting natural gas over long distances via pipeline can be very expensive and susceptible to disruption.

LNG is simply natural gas cooled to approximately -163ºC (-260ºF) at close to atmospheric pressure. At this temperature, its volume is reduced to about 1/600th of that at ambient temperature, which makes it much more economic to transport by sea in specially designed ships.

In order to do this, plant must be constructed that can liquefy (refrigerate) the gas. The gas must then be transferred onto ships, carried across oceans, offloaded into onshore tanks and stored, all at -163ºC. It must then be regasified for use in homes, heating, transport and industry.

LNG facility construction at CB&I
CB&I specialises in providing turnkey liquefaction and regasification plant comprising terminals, tanks and other systems. These facilities usually include special refrigeration equipment to maintain the gases in a liquefied form. It also provides LNG tanks on a standalone basis. Process equipment and cryogenic tanks are built from special steels and alloys that have properties to withstand temperatures as low as -163C, which is the temperature required to keep the gas in a liquid form.

Currently, CB&I is executing two major LNG EPC contracts in the UK: South Hook LNG in Wales and the Isle of Grain Expansion Project in Kent. The Isle of Grain Project is using Welding Coordinator.

The Isle of Grain LNG facility is located on the River Medway, approximately 30 miles east of London. It was originally commissioned as an LNG peak shaving facility. In 2005, the facility was converted to an LNG import terminal, with an initial capacity of 3.3 million tonnes of LNG per year. CB&I won phase two of the facility expansion and has EPC responsibility for the project, which included three 190 000 m3 full containment tanks, a control and administration facility, and associated systems. This phase is on target for the additional capacity to be available winter 2008/09.
In 2007, CB&I won the contract for the third phase of expansion. Under this contract, it will construct a new jetty capable of berthing LNG carriers with a capacity up to 265 000 m3 and with an unloading rate of 12 000 m3/hr. The work scope also includes the construction of another 190 000 m3 full containment LNG storage tank and new gas processing facilities. This work is scheduled to be completed in 2010.

The LNG tanks being constructed at the Isle of Grain facility are full containment tanks. These tanks are comprised of an inner open-top 9% nickel steel containment tank to hold the liquefied gas, which is itself contained within a steel-lined reinforced concrete outer containment tank with a roof. The space between the inner and outer containments is insulated to maintain cryogenic temperatures. The outer tank provides containment of liquefied gas vapour, and in the unlikely event of a leak provides a secondary containment of liquid and controlled release of vapour.

LNG tanks are made from a variety of materials including:
• Carbon steel, which is used to form the roof structure and the outer liner (vapour barrier) among many other components and structures
• Aluminium, which is used to fabricate the suspended deck that forms the “lid” of the inner tank and becomes the platform for supporting insulation blankets. These provide further insulation to maintain cryogenic temperatures
• 9% nickel is used on the inner tank, which actually contains the LNG. 9% nickel is used due to its ability to maintain toughness at extremely low temperatures.  

These different materials require different welding procedures and differing inspection criteria. For example, the outer liner requires 100% vacuum box testing and 100% liquid penetrant testing. The 9% nickel inner tank requires 100% Auto UT of all butt-welded seams on the shell and a percentage radiography cross-check of all weld intersections, as well as 100% penetrant testing and 100% vacuum box testing of all welds above the hydrotest level.

The testing and verification of welds is obviously a vital part of the fabrication of LNG plant, to ensure compliance with health, safety and environmental legislation, meet international quality standards, and meet client requirements within cost and time. The management of the documentation of this testing and verification through the use of software is seen by CB&I as an important method of saving time and managing resources.

Welding Coordinator software
Welding Coordinator was originally developed by TWI as a software tool for tracking production welding projects. It was originally developed as a number of discrete customised systems, each matching the specific requirements of individual companies. There is no industry standard that specifies exactly how this information is managed. Consequently, every company carries this task out in a different way, depending on the product being made, the QA requirements of the project and the background of the responsible engineers.

In 2004, TWI developed an off-the-shelf Welding Coordinator tool that had many configuration facilities built in. The advantage of such an approach is that TWI has only one software product to maintain and the end-user company can configure the software itself.

The software is based around the concept of a weld data sheet, otherwise referred to as a weld map, a weld tracking sheet or a weld history. A weld data sheet comprises a header that describes the scope of the data sheet, a footer containing sign-offs and a table of welds. Each row in the table represents a weld, and the columns in the table are configured to match the data storage requirements of the project. A typical weld data sheet is shown in Figure 4.