CLOSING BIGGEST BORE

Taupo Times, Volume II, Issue 71, 27 May 1953, Page 1

CLOSING BIGGEST BORE

How It Was Done Fhe deepest geothesrmal steam. bore at Wairakei, reaching a depth of 2020 feet, which was "blown off" on Api.il 24th, was closed down on Sunday, May 17th. As mentioned in the Times of May 13th, it had been found tfcat the valve controlling the opening of the ten inch pipe would not eiose completely. Consultations were then held between the Drilling Superintendent, Mr JR. McMillan, and the mechanical engineers of the Ministry of Works associated with the Geothermal Projeet, hfeaded by Mr D. S. Gtrinter, and plans were made to overcome the difficulty. O11 Saturday, May 16th, these plans were put into effect and the bore was sueeessfully shut down next day.

New Valve Fitted The equipment designed to enable the bore to be brought under control eonsisted of a length of pipe which would fit over the ten inch bore pipe, to the top of which was fitted a valve of the type being used on the projeet. The plan was to slip this equipment, with the valve left open, over the big steaiu jet, slide it down ifhe pipe and then weld the bottom end securely thereto. To anyone familiar with the steam bores at Wairakei and in particular with the oue under discussion, it will be apparent that the execution of the plan was unlikely to be quite as simple as the explanation sounds. Though Ihe bore was partly closed, the steam jet was still roaring upward under great pressure. A big mobile crane, manoeuvred by a tmetor, was used to feandle the equipment, and as this was backed toward the bore, with the massive pipe and valve suspended from it, fchere was keen interest among* the spectators. To the bottom end of the pipe steel rods had been welded in the fo'rm of a cone, to assist in guiding it onte the top of the bore pipe. Stay ropes were fastened to $h© suspended equipment, some car*ed to nearby tree stumps, others to motor trucks and a bulldozer. When all was ready, a sign-al ftrora the Drilling Supeiintendent brought the mobile crane into movement, and the pipe was slowly moved and lowefed toward the top of the bore, its progress controlled by signals from Mr McMillan to the men in charge of fhe stay iropes. Quicker than had seemed possible the guiding ring* of J the conical attachment aiready men- 1 fcioned was lowered over the bore held by the ropes against the presgure of the steam jet and in a few mijiutes more rnost of the steam was foaring from the open top of the new fittmg. Although there was still much to be done, this seemed, to thoee watcihing the job, an assuranee that the problem of closing the hore was almost overcome.

Welders* Diflficult Job Once the new pipe had been slipped over the original ten-inch one, a welder with an oxy-acetone torch i mt from it the conical guiding attadhment, enabling it to be slid down the bore pipe as far as the original walve fitting would allow. The welding staff, under the direction of the Chief Welding Supervisor of the Ministry of Works, Mr Granger, then fcegan the job of electric welding the two pipes together. This work, done m the concrete dug-out immediately beneath the open bore, in clouds of steam and conditions of noise ancl vibration which needed to be seen to be realised, and with hot water falling eontinuously from the bore just above, was a job done under the most difficult Jirtumstances. Its successful completion reflects great credit on the whole of the welding staff. While ihe welders were commencing their

job, the engineering staff completed the staying of the new pipe by means 1 of steel rods and turnbuckles to fast- ! enings set in conerete. The final details of the work were completed on j the following morning and the valve was then closed. The biggest bore was undef eontrol and another problem had been sueeessfully solved.