KiwiRail is using a rail maintenance contractor it temporarily stood down in Auckland earlier this year over "faulty" track welding, saying it's confident crews have been sufficiently retrained.
RNZ could reveal the contractor, which carried out improper welding on train tracks in a Parnell tunnel over the Waitangi long weekend - also carried out "serious" defective work in a City Rail Link (CRL) tunnel around the same time.
These details emerged through correspondence released to RNZ under the Official Information Act.
The severity of the CRL welding faults were initially deemed to be "major", and had the potential to cause "serious/life changing injury or long-term impact to environment", according to an incident report.
Rail operator KiwiRail said there was no risk to the public as no trains were being tested on the yet-to-be-opened CRL tracks during that period.
No passenger rail services in Auckland were running that weekend on other parts of the rail network. KiwiRail said temporary fixes were put in place before they resumed on February 9, followed by permanent fixes.
Of the 10 welds completed by this contractor in the CRL tunnels from February 6 to 8, four were found to be faulty. In Parnell tunnel over the same period, eight out of 28 welds were defective. These were much higher than ordinary failure rates, according to KiwiRail.
The discoveries prompted KiwiRail to test all of this contractor's welding work in Auckland since Christmas last year - 470 welds over 14 sites.
It has tested 70 - about 15 percent of the total - as of mid-May, with no further faults detected.
KiwiRail said it had made further progress since then. RNZ asked for updated figures.
Details of the costs of remediation, or any other penalties, were deemed commercially sensitive and not released to RNZ.
KiwiRail chief metro officer David Gordon said it had taken time to develop testing techniques, and he expected to complete all remaining weld assessments "in the coming months".
"This is a promising result, which points at the issue being largely limited to Waitangi Weekend work in the two tunnels.
"Welds in tunnels can be more difficult compared to welds on open track, given the underground environment."
The issues related to preparation, finishing and clean-up processes in flashbutt welding, which joins tracks together by heating ends of two metal pieces and pressing them together.
Gordon said the improper welding meant there was risk defects that could form.
KiwiRail has not publicly named the contractor. Photo: RNZ / Samuel Rillstone
The contractor voluntarily stopped its other work in other parts of the country, while initial investigations were ongoing in Auckland. They resumed work in mid-March after undergoing a training programme.
KiwiRail had not publicly named the contractor.
It said the company remained a "trusted party" cooperating with its processes, and that identifying them would "unreasonably prejudice" its commercial dealings.
"Following their retraining and re‑certification, KiwiRail is confident that welding work can safely resume and will meet the required engineering standards," it said.
"The contractor in question is experienced and has previously been very reliable."
A wider engineering review is ongoing into welding standards, all contractors' practice and the speed of fault detection.
The welding work was done as part of the city's track upgrade programme, in preparation for CRL's opening later this year.
Auckland Transport said the faulty CRL work had not impacted its opening date.
Asked about KiwiRail's decision to continue the use of this contractor, Rail Minister Winston Peters said he was satisfied with KiwiRail's response "as it confirmed to us that they took the faulty welds as seriously as we did".
The rail operator told the contractor to stand down from its CRL work after KiwiRail engineers observed "questionable welding technique" between Te Wai Horotiu and Karanga a Hape stations on February 7.
According to correspondence sent by a KiwiRail staff member, it was this discovery that prompted engineers to carry out further testing at Parnell tunnel.
Initially 10 welds were tested in Parnell tunnel on the evening of February 8. This revealed six faults, which were secured with metal plates and clamps as an interim fix.
The Parnell tunnel was reopened to passenger rail services on the morning of February 9, with a temporary speed reduction as a precaution. No freight trains had travelled through the tunnel that day.
Asked how KiwiRail was confident in its decision to re-open the Parnell tunnel, given a number of welds in the area were yet to be tested at that point, KiwiRail's Gordon said "there was no indication of issues with any other welds", though the agency had decided to do a further review of the contractor's work "for completeness" given the "unusually high failure rate".
KiwiRail usually tested 50 percent of all new welds within four weeks, though the agency said this rate had been higher in Auckland in recent times given the amount of welding being done.
This set off worry among engineers as the day progressed: having identified the contractor's 18 other welds in the Parnell tunnel over Waitangi weekend, there was a risk that a similarly high rate of failure would exceed the number of plates and clamps readily available in Auckland for temporary fixes.
That prompted KiwiRail's decision late on February 9 to close the Parnell tunnel to passengers the following morning, which had the potential to cause disruption to thousands of train commuters in the south and west of the city.
"Clamps are being brought in from other parts of the country, but we cannot confirm they will arrive and can be fitted overnight before the morning peak," a KiwiRail staff member wrote to a number of stakeholders - including Auckland Transport, passenger service operator Auckland One Rail and the Rail Minister - that evening.
"If they can, we will carry out the work as quickly as possible and there is a remote chance we may not have to close the tunnel."
In a statement to the public shortly after, Gordon said KiwiRail "appreciate how frustrating this is for Aucklanders".
Testing of the remaining welds that evening revealed only two further faults. That meant there was enough equipment in Auckland to carry out repairs to reopen the tunnel on February 10, before the morning rush hour.
KiwiRail extended the contractor's stand-down to cover the rest of the Auckland network.
"Clearly this is a serious issue that needs to be worked through, and all details thoroughly analysed to understand what has happened at both locations that has led to failed tests," the contractor said in a response to KiwiRail.
On February 10, Gordon told Morning Report the contractor was "mortified" about the work, though accountability ultimately rested with KiwiRail.
A staff member in the Rail Minister's office emailed Gordon and other KiwiRail staff later that day, showing Peters had sought assurances about welding assessments, remediation costs and said "commuters should not have been inconvenienced by third world faults".
Asked if he stood by this characterisation, Peters told RNZ: "Commuters should not have been inconvenienced by third-world faults.
"If the welding was done correctly, they wouldn't have been inconvenienced."
-RNZ