Extremely high pressure testing at TWI's Cambridge laboratories took a step forward recently with the completion of a large subterranean pressure test pit. Serving the engineering needs of the oil and gas sector in particular it is believed to be one of the best equipped facilities of its type in Europe.
The establishment of the new test facility is linked with the start of a Group Sponsored Project on strain based assessment of pipeline girth welds. The specimen under test will be both axially strained and pressurised simultaneously.
'The idea is not necessarily to take it to destruction' explains project consultant Henryk Pisarski. 'But we are applying very high loads at extremely high pressure, up to 1000 bar. The pipe will be strained considerably, in a four point loading test or in tension in a modified wide plate rig. In each case it will be strained beyond its yield point. There will be an intentional crack within it so the potential exists for things to go wrong. 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'.
What makes the TWI facility so special is the back-up support offered behind any test work it performs; 'We will 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. We are 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'.
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 individually removable.
Specimens will be craned into the chamber using a pair of 3t capacity A-framed gantries. 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 ground the entire installation is housed within a large steel fabricated out-house, equipped with mains and communication services. These include video monitoring and recording equipment 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.
'Since this construction has been underway we have been approached about testing a sample from a pipeline containing in-service damage to assess its fitness for continued operation.'
Now that there is an established controlled facility, rather than building a temporary structure for each new project, it is expected that a number of short notice projects related to internal pressure testing and external loading will be undertaken. Already there are half a dozen jobs on the waiting list 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
