Thermographic inspection spots subsurface flaws

Edited by the Engineeringtalk editorial team Jan 7, 2004

Thermal Wave Imaging has been awarded a contract to assist NASA in developing procedures and best practices for thermographic inspection of the thermal protection system on the space shuttle orbiter.

Thermal Wave Imaging (TWI) has recently been awarded a contract to assist NASA in developing procedures and best practices for thermographic inspection of the thermal protection system (TPS) on the space shuttle orbiter.

The contract is part of NASA's effort to resume shuttle flights and improve preflight inspection in the wake of the Columbia accident in February 2003.

In addition to TWI, project team members include scientists and engineers from the NASA Kennedy, Langley and Marshall centres, and NASA contractors Boeing and United Space Alliance.

The team is using the TWI EchoTherm system to inspect the reinforced carbon-carbon (RCC) panels on leading edges of the shuttle's wings, a portion of which was speculated to have been damaged by piece of foam that became detached from the external fuel tank during the Columbia launch.

Although the Columbia investigation report recommended more comprehensive inspection of the leading edge before future shuttle flights, the RCC is a difficult material to inspect using conventional technologies, such as X-ray or ultrasound.

NASA has determined that pulsed thermography is one of the few methods capable of detecting subsurface flaws and irregularities in the protective silicon carbide coating.

Under the present contract, TWI will identify and recommend modifications to inspection procedures and equipment to facilitate the unique properties of RCC, as well as the physical configuration of the shuttle.

TWI has a long-standing relationship with NASA, and has provided nondestructive inspection equipment to the Kennedy, Langley, Marshall and Lewis centres, as well as to NASA contractors including Boeing, Lockheed-Martin and United Space Alliance.

Most recently, TWI completed a Phase II Small Business Innovative Research (SBIR) contract with the Marshall Space Flight Centre for the development of a hybrid thermographic system to detect kissing disbonds in composite materials.

According to TWI Physicist and President, Dr Steven Shepard: "The extreme temperatures and stresses that the orbiter experiences on re-entry create a set of conditions that can make a small, hidden defect grow very quickly and lead to catastrophic failure.

As a result, it becomes necessary to do a very detailed inspection on these large components, which is exactly what our equipment is designed to do.

We are pleased to be working closely with NASA to refine the process for inspecting the shuttle's leading edge".

TWI is the world leader in the development and commercialisation of systems for thermographic nondestructive testing.

In pulsed thermography, the surface of a sample is heated with a pulse of light, and an infrared camera is used to monitor the resulting temperature changes.

TWI's EchoTherm and ThermoScope systems use a patented Thermographic Signal Reconstruction method to extract information about subsurface structure from the temperature data, and create an image that can be used to measure properties such as thickness, or reveal flaws such as voids, delaminations or inclusions.

TWI systems are widely used in the worldwide aerospace, power generation and automotive industries by companies and institutions including Northrop-Grumman, Rolls-Royce, Ford Motor Co, General Motors, and the US Navy and Air Force.

Thermal Wave Imaging is represented in the UK and Ireland by LOT-Oriel.