TWI Bulletin, January - February 2011
Case Study: New pressure test chamber commissioned
Extremely high pressure testing at TWI's Cambridge laboratories entered a new era recently with the completion of a large subterranean pressure test pit. Serving the engineering needs of the oil and gas sector in particular it's believed to be one of the best equipped facilities of its type in Europe.
'Historically we've made quite a name for ourselves using a small pit in the old engineering laboratory' says project consultant Henryk Pisarski. 'In the past we've even performed large pipe tests in the car park by embracing the test specimen with heavy pre-cast concrete panels to absorb the sudden release of energy. It's worked well, but nowadays we're doing more and more of this work, so a permanent installation, compliant with increasingly stringent 2010 health and safety demands, is the obvious answer.'
The advent of the new test facility has largely been triggered by a group sponsored project on strain based assessment of pipeline girth welds. The specimen under test will be both strained in bending and pressurised simultaneously.
'The idea is not necessarily to take it to destruction' explains Pisarski. 'But we're applying very high loads at extremely high pressure, up to 1000 bar. The pipe will be bent considerably, in four point loading. It'll be strained beyond its yield point. There'll be an intentional crack within it...so the potential exists for rapid fracture. Without a remote pit like this you run the risk of damaging adjacent laboratory equipment, so we decided now is a perfect opportunity to build a dedicated facility'.
Pisarski believes that what puts TWI's facility in the forefront is the huge back-up support offered behind any test work it performs; 'We'll pressurise it of course, but perhaps the client will want it to be strain gauged and instrumented. We can do that. Perhaps the client even wants the event to be filmed...not a problem. We're able to say 'this is what we recommend'. And then we can carry out all the material behaviour analysis, if and when it fails. Whatever happens, we can do all the post-test investigation under one roof because we have all the metallurgists and engineers and equipment we need here at TWI. We can also compare the reality of the test with the results of numerical modelling, which can also be conducted at TWI'.
For a third of a million pounds TWI certainly has an impressive installation. Measuring eight metres by three in plan, the 2.5m deep reinforced concrete bunker comprises a metre thick floor with 700mm thick walls. The multi plate flat roof is made from eight 25mm thick steel plates, each of which is individually removable.
Two heavy section reaction beams - they are actually extremely thick section Universal Columns - can be bolted down across the pit at the same level as the roof, to enable four point bend tests to be conducted beneath.
Specimens will be craned into the chamber using a pair of 3t capacity A-framed gantries. So provisionally the pit will be able to accept specimens up to 6t in weight. Both hydraulic and pneumatic tests will be possible in either static or dynamic loading regimes.
Above the ground the entire installation is housed within a large steel fabricated building, equipped with mains and communication services. These include video monitoring and recording kit dedicated to receiving digital signals from in-chamber cameras and test piece instrumentation.
Inside the pit two large diameter conduits have been installed at mid-height in the northerly wall to allow access for all instrumentation and communication services to be run between the specimen and the control centre.
'The facility is very suitable for testing a sample from a pipeline containing in-service damage to assess its fitness for continued operation' adds Pisarski.
Indeed the future is already rosy for his team. Now that it has an established controlled facility, rather than building a temporary structure for each new project, it is expecting a number of short notice projects related to internal pressure testing and external loading. Already there are also half a dozen scheduled tests related to last year's destructive testing of electrical resistance welded pipe. To learn more about TWI's new pressure test facility contact: henryk.pisarski@twi.co.uk or phil.robinson@twi.co.uk.
