I am in full agreement that the average Marine surveyor
has not the experience or qualifications to under take full Ultra sound work
other than the perhaps the normal thickness testing, but
, if that degree of examination is required or asked for I'm sure every Surveyor I know would happily point the client in the right direction to gain such expertise, that said professional bodies such as the IIMS-Lloyd's with whom I am a full member
have VERY high standards with training required on all Survey
equipment, The IIMS run a points system for training/knowledge that must be met yearly other wise you loose your standing(so keeping up to date is mandatory), I'm not sure re American societies and their requirements,
Here's a few issues/points in reality regarding Ultra sounds on hulls etc versus static inspections in controlled situations:
-Ultrasonic signals don't like traveling through air. As a result, foam core
acts as a significant barrier to signal penetration. If you are concerned with detecting water
intrusion into core- use a moisture meter. If you would like a global image of water
intrusion into a cored hull
, then thermal imaging is your best bet.
-Low tech laminates like thick, hand laid hulls fiberglass
tend to have many tiny air bubbles that cumulatively tend to disperse a UT signal. In some cases, UT is like using a scalpel when a blunt instrument would suit you fine. There are times when you just need to break out the hammer and grinder, mate.
-UT sends out a signal that is a beam. The thicker the laminate, the lower the transducer frequency and the wider the beam. This can limit the ability send signals into tight spots such as inside corners.
-The A-scan UT that field units offer cannot produce a pretty, global, color picture of the entire part. The only way to get that is with a monstrous jig and a robotic arm such as you would see in a production setting. The accuracy and information is the same- it's just that the individual wave forms cannot be collated and plotted into a single
-UT records separate waveform images
as you scan the part. You need to be realistic in deciding what size defects are significant as well as what kind of inspection grid you need to set up on the boat
. You can't expect to ferret out every 1/4" bubble in the hull of an 80' boat. Well, you could...but you wouldn't want to pay me the time it would take to do it!
There is no single magic inspection tool that is ideal for all situations. Ask anyone in the composites industry and they'll tell you that marine
structures can be horrendously difficult to inspect when compared to more conventional production laminates. UT is particularly adept at assessing the following situations:
-Solid vacuum bagged carbon spars. The same clean, dense laminates that make it virtually impossible to detect subtle damage with a hammer are easily scanned with UT. Ultrasound will not only tell precise overall thickness, but also the depth
of the defect/anomaly. Poor consolidation (loss of bag pressure), dry fibers, and voids are all good examples of detectable flaws.
-Bond line issues. Ultrasound can pick up the transition between skin coat and structural laminate. A clean line will transmit the signal, where a delamination
or "never bond" will show a clear interruption on the waveform.
-Secondary bond damage. As noted above, UT can pick up delamination
fairly quickly. There's no need to tent off and demolish the interior
of the boat in order to determine the extent of damage.
-Quality Assurance. A new part can be scanned to check for defects and laminate consistency. Critical areas of the part can be scanned and the readings can be archived so that, in the event of future trauma, the part can be scanned again to see if there are any anomalies compared to the "as built" baseline readings.
I offer the forgoing only as advice with no preconception, with no legal
implications and without prejudice.
Regards Steve Warren (MIIMS-Lloyd's Accredited)