Welding's role in delivering electricity infrastructure programmes

Heading: 


As presented by Mr Morris Maroga at the IIW Regional Congress and co-authored by Mr Matshela Koko and Mr Morris Maroga/>


Issued by Trinitas Consulting on behalf of SAIW/>

In the current Eskom capacity expansion programme, the key challenges include; skilled labour shortages, cost escalation and schedule delays on mega projects such as Medupi, Kusile, Ingula and transmission strengthening projects.

A central challenge for Eskom is the productivity and supply of skilled welding and non-destructive testing specialists. Eskom expects to use up to 2000 specialist welders until 2015 at Medupi and Kusile power plant construction sites, but will remain reliant on foreign welders since the industry is not able to train local welders fast enough to do the job reliably and productively.

The hiring of Asian welders by Hitachi brought work at Medupi construction site to a halt during the month of May 2011 and impacted severely on the Medupi schedule.

Of the 161 A-Class welders working on Medupi boiler 6, only 14.3% are South African welders. There are 181 structural steel or B-class welders qualified to weld FCAW and 24 SMAW welders working on Medupi boiler 6.

All of these welders are South African, implying that the South African welding industry is able to train enough B-class welders but only a few A-class welders. The reject rate of the South African welders is comparable with that of the international welders.

Maroga holds that welding is a critical enabling technology for securing of electricity supply for South Africa, now and in the future. Eskom and the welding industry in South Africa need to define the issues and opportunities that must be dealt with immediately and up to 2030 in order to enable South Africa to double its installed generating capacity by 2030, as envisaged by the IRP2010.

Over a period of 19 months a total of 34 552 A-class welds have been completed at Medupi boiler 6 and a staggering 141 941 A-class welds were completed during the maintenance of Generation Fleet. This is only the beginning; as Generation Fleet is ageing and requires major refurbishment and new build projects such as Medupi and Kusile reach their peak, more welding will be required.

At Medupi the average rejection rate was 13.2% with the best welder having a rejection rate of only 3.2%. An average reject rate of 13.2% is unacceptable and can be brought down with good training and development of welders at early stages of their careers, combined with adequate supervision and inspection.

Maroga holds that the South African welding industry needs to train and develop enough welding personnel to maintain a consistent 3% rejection rate per welder.

Only then can the focus be to improve the production rate. The poor production rate impacts on project schedule or the PCLF (Planned Capability Loss Factor). The actual welds completed fall behind the planned number of welds every week, thus impacting on the planned completion date. Both the weld reject rate and actual production rate have an impact on completed welds.

The major causes of the weld failures are due to poor workmanship, such as defects which arise from the inherent variability of the welding process or an error by an operator or welder. Only 0.1% of the weld failures are attributed to technological failure such as inconsistency in the welding operation, i.e. use of the wrong electrodes, incorrect heat treatment or inappropriate joint design.

According to a United Kingdom case study which has a rejection rate of less than 1%, a well structured training programme of welders and fitters, refresher training, mentorship during training and welding schools with their own NDT facilities are factors that contribute to welding quality.

Welding supervision with a ratio of 1:10 is very important. Furthermore, the keeping of a database of all welders should be used to control the performance of the welders. The same welders should be used for maintenance, refurbishment, ensuring the intellectual property in the project is maintained and trusted welders with a good record will be readily available.

Failure and recovery methods should be documented with every rejected weld investigated in order to determine the cause of the failure.

The investigation should be detailed and an analysis of welding machines, consumables, weld job cards, welding visual inspection records, welding supervision and welding conditions should be undertaken. Where causes for rejection are determined, steps should be taken to avoid a similar occurrence in future.

In order to minimise the effect of the high rejection rates on the completion dates of the new builds Eskom established the Welding Performance Improvement Program aiming to address welding quality and productivity.

The programme aims to create a sustainable welding skills base in the power industry to achieve world-class welding performance. It will also aim to boost ongoing skills development, reduce foreign exchange losses, reduce or eliminate the cost associated with weld repairs and drive the rejection rate to 3%.

This is not a task that Eskom can undertake on its own however and it calls on industry to train enough B-class and A-class welders and to standardise on the minimum requirement for welding personnel training in order to produce artisans with high quality of skill.

"We need educated people holding the welding torch because they need to understand what happens at the end of the torch,' says Maroga. "We need well structured training programmes, well educated instructors, a quality culture that treats every rejection as serious and a way of rewarding good welders, especially those that can keep the rejection rate consistently less than 3%'.

What do you think?

Comments