Tech feature of the month: Inspector gadgets
NDT inspection and testing technology goes under the microscope
The latest inspection and testing technology has reached new levels of accuracy and sophistication, but is it worth the high cost?
Words: Oliver Ephgrave
Non-destructive testing (NDT) is a crucial technique for inspecting oil and gas facilities and many different methods are available, from the rudimentary visual inspection to high-tech scanning devices.
According to Billy Harkin, managing director of UAE-based Megarme, the region’s oil and gas facilities have reached a stage where NDT is critical. “The NDT industry is definitely growing in this region.
Oil and gas are still heavily in demand and the facilities that produce those commodities are very important.
As the UAE is now over 30 years old, a lot of rig facilities have to be assessed for operational life expectancy. On a tubular structure, you can see the outside but you don’t know the condition on the inside. Replacement of these assets is a lot of money and NDT is essentially asset management,” he says.
Harkin’s point is reiterated by Craig Pitts, Megarme’s business development manager of oil and gas projects in the Middle East, Caspian and Africa. Pitts adds: “NDT falls under critical maintenance.
For instance, a small jack up rig in the Caspian Sea is rented at US$450,000 a day. If pumping is halted due to maintenance then a lot of money will be lost.”
Aside from preventing costly maintenance work, NDT is also crucial for guarding against catastrophic failures. “Preventative maintenance is key. The cost of getting it wrong is enormous – to both the company and the country. There have been enough high profile incidents to show this,” says Harkin.
Pitts continues: “Recently we did an inspection for one of our clients and we detected some critical cracks on an operational load bearing structure. This shows the importance of NDT as the cracks could have led to something catastrophic. These linear indications are not visible to the naked eye.”
Harkin reveals that his company evolved due to the opportunities in the NDT industry.
“We started as a rope access contractor but we have expanded our scope and evolved as a company. Since 1st Jan 2010 we have developed a complete inspection and engineering division and NDT now accounts for a significant part of what we do – it’s a very progressive area of our business.
We identify the weaknesses in a structure and we also carry out the post-inspection work such as welding, repairs, removing the structural members, blasting and painting over the top.”
He states that rig owners are demanding faster inspection procedures, and that Megarme’s rope access specialism provides the answer.
“Every day that a rig spends in a dry dock it’s not making money. Unlike scaffolding, our system is mobile – the equipment is in a backpack.
Therefore you can carry out an inspection and receive a report before the rig arrives in the port or dry dock. That can save a week to ten days’ time in the dry docks. It’s difficult to erect scaffold when you’re surrounded by water.”
According to Pitts, the three main forms of NDT are Magnetic Particle Inspection (MPI), Ultrasonic Testing (UT) and Electromagnetic Testing (ET).
Yet he points out that the more advanced technology is now widely implemented. Harkin elaborates: “Conventional NDT, such as MPI, usually involves the use of very heavy duty hydro-blasting equipment.
You have to blast off all the paint on all the weld, then carry out the inspection. Post-inspection would involve re-painting, even if no repair work was necessary.”
Harkin continues: “Nowadays we have technologies such as Alternating Current Field Measurement (ACFM) which scan for cracks without removing paint. With traditional NDT you can only see the location of a crack – you don’t know how deep it is.
You have to keep grinding until you reach the base of the crack. With the advanced NDT technology you can get a full 3D image and you don’t have to remove paint.”
He states that the advanced techniques are sometimes viewed with caution. “We have to introduce our clients on the latest technology, which is being used in the North Sea or North America.
It sometimes takes one or two years to sow the seeds. People don’t like change so you really have to show them the benefits. You just need the first job then the enquiries start coming – that happened with ACFM.”
Pitts notes that price often deters rig owners from investing in the advanced NDT techniques. He adds: “These technologies are getting more and more expensive and that’s one of the reasons that companies don’t invest in them. Many think that conventional NDT is fine.”
However, Harkin believes that the benefits outweigh the higher costs. “There is no room for human error as there is so much detail in the reports. The technology is more expensive to buy and maintain but it cuts out a lot of work.
And given what’s at stake, it’s better to spend a bit more money on the newer technology to make sure everything is sound.”
Although both Eddy Current and ACFM are considered to be advanced NDT techniques, Harkin believes that the latter technology is superior. Pitts adds: “A couple of years ago, hardly anyone was using ACFM – Eddy Current was the best way of detecting cracks through paint.
Eddy Current is still widely used but the ACFM technology is now becoming a real contender in terms of accuracy. Clients are now recognising ACFM as a very reliable form of inspection.”
Mohamad Shaheer Naranath, head of inspection and engineering for Megarme, elaborates on the merits of the ACFM technology over Eddy Current.
“In the past, the testing technique preferred on offshore components over coating was Eddy Current. The method is sensitive to many physical and metallurgical variables, thus it has wide application, provided the variables which are not of interest can be eliminated or suppressed.”
However, Naranath states that it is more difficult to achieve accurate readings with Eddy Current due to the number of variables.
He adds: “Eddy Current tests respond to electrical conductivity, magnetic permeability, geometric properties of the test objects, the presence of discontinuities within the test material, test frequencies, end effect, lift off, skin effects, etc.
On site conditions it is not easy to suppress all the variables except the discontinuity signal and interpret the test results of ferro magnetic material.
All these variables, including the cracks, produce display signals and some of them are very similar to cracks. It takes a well-trained operator to discriminate between a crack and a non-crack signal.”
He continues: “Eddy Current equipment is calibrated mostly to drilled holes, milled or electrocharge machined slots. The artificial defects used for calibration are not a true representation of cracks usually seen in the ferro magnetic weld joints. Hence distinguishing between a defect and noise signal is difficult with Eddy Current equipment.
Naranath believes that ACFM overcomes the demerits of Eddy Current. “ACFM has been widely been accepted by the oil and gas, petrochemical and marine industries for in service inspection. As the equipment is capable of operating through paint, a sound coating need not be removed for inspection.
The ACFM technique works on electromagnetic principle and is suitable for the testing of ferritic steels, austenitic stainless steels, aluminium, duplex, super duplex, monel, inconel and titanium. It has also been used to test through flame sprayed aluminium, epoxy coating, standard paints, ferrite-based paints and copper coated threads.
“Unlike Eddy Current testing, the ACFM technique is generally insensitive to permeability, metallurgical changes and lift off. The ACFM probe is delivered with an individual software file, which sets up the instrument to give the best available performance. Since the technique is relatively insensitive to lift off, it can be used to test through coatings.”
ACFM has been approved by certifying authorities – including Det Norske Veritas, Lloyds Register, Bureau Veritas, Germanischer Lloyd.
Yet Amaresh Majumder, specialist inspection manager for UAE-based inspection provider Inspec, points out that ACFM is more expensive than Eddy Current.
He adds: “There is, however, a technique of Eddy Current that uses saturated probes and has wider applications than standard Eddy Current. It is already used in Europe – we have seen demonstrations and we are hoping to buy it in the next two months. It is a good solution.
It doesn’t do everything that ACFM offers, but ACFM is more expensive,” he says.
Majumder reveals that the key NDT markets for Inspec include Dubai, Abu Dhabi, the UAE’s Northern Emirates as well as Oman, Qatar and Saudi Arabia.
Meanwhile, Megarme’s main areas of activity are Dubai, Abu Dhabi, Qatar, Oman and countries bordering the Caspian Sea such as Azerbaijan and Kazakhstan. Harkin says: “Qatar, Abu Dhabi and Dhabi are very stable bases for us and we can fly to many destinations. Abu Dhabi is difficult to penetrate but once you do there’s an amazing amount of work.
There is great potential in South America but this is too far for us. We want to stay strong in the Middle East and concentrate on our doorstep.”
He adds that many projects have been postponed due to the recent unrest in the wider Middle East. “There is a lot of work in Egypt but we have had to demobilise due to the unrest. Libya was a market that we were going to target this year, but that has now been taken out of the equation,” says Harkin.
Pitts identifies the Caspian Sea as a region of great potential for NDT specialists. “The Caspian is one area where corrosion monitoring is in demand due a highly corrosive environment.
They have a lot more issues than the Middle East. We are proactively bringing new technologies and techniques into this region,” he adds.
Yet Pitts is quick to highlight that it’s a constant challenge to remain on the ball due to the fact that NDT standards are constantly evolving.
“You never have a full arsenal of what is required for NDT. It’s always moving and you will never be on top of it. We recently had a request for ‘post-tow’ inspection.
We’d never done this before but it was a great success. You’ve got to keep evolving. There are probably technologies in the market that will supersede ACFM eventually. It’s actually very exciting for us – no two days are the same.”