Robert Young of Applus+ RTD USA describes a solution for challenging inspections.
There is a growing need to develop more versatile and cost-effective inspection solutions for pipelines and pipe sections previously considered ‘difficult to inspect.’ While the majority of pipelines in high consequence areas are piggable, most facilities, including hydrocarbon processing, power plants, terminals, pump stations, compressor stations, oil/gas gathering and offshore and subsea systems require non-traditional solutions due to both design and operational constraints.
Design challenges may include short radius and back to back bends, absence of pig launchers/receivers, single access systems requiring bidirectional flow and unique pipe materials.
Pipeline operating conditions such as low or high pressure or flow, temperature and line cleanliness, require an engineered solution to ensure the highest quality information can be collected, while addressing the threats specific to the environment and pipe materials.
A large terminal operator approached Applus+ RTD to provide an inspection solution addressing its operational and system design challenges. Terminals are complex, with hundreds of miles of piping, including lines for loading to dock, truck and rail, along with internal piping to facilitate product storage, movement, blending and storage tank circulation. Marine terminals experience constant visits by oceangoing tankers alongside the intermodal transportation activities of rail, truck, storage and pipelines. Given the terminal’s proximity to the marine environment, preventing an incident or leak from occurring became Applus+ RTD’s client’s top priority, along with assuring system reliability providing the client a competitive advantage by reducing the unloading time spent by each tanker, truck or railcar in the facility.
Case study details include:
- 8In loading lines, insulated
- 1590 feet
- 306L stainless steel
- 0.13 inch wall thickness
- No launchers/receivers
- Insertion of DTI Trekscan tool into nominal pipe.
- Single line configuration (non-looped)
- Back to back 1D bends
- 72 hour (max) notice for inspection
- Less than 24 hours for preliminary reporting
Applus+ RTD has a long history of technology development and a diverse portfolio of traditional and advanced non-destructive testing (NDT
) techniques and applications to inspect the outside and inside of piping or structures. The objective of NDT is to detect flaws in the pipe and characterise them by their size, shape and orientation so that a decision on fitness for service can be made.
Very early in the project it was decided that an internal inspection technique (rather than an iterative external evaluation) was preferred. This decision was made due to the time consuming and expensive process of removing and reapplying insulation, attempting to screen affected areas and ultimately assessing the pipe conditions utilising external non-destructive evaluation methods in challenging to access locations. DTI Trekscan
, an ultra-high resolution ultrasonic inspection
solution was the chosen technology as it provides 100% overlapping inspection of the pipe internal and external wall and has the versatility to meet the timing associated with the limited line access and design challenges of their system.
The terminal application
Due to the near constant shipments in and out of the terminal, line availability was limited and the project was required to function efficiently with well-coordinated logistics between the client and contractors in an already busy and congested process environment, all within a 72 hour window.
The scope of work included:
- Line preparation and cleaning
- Pumping services and water management
- Configuration, tool testing and execution of successful inline inspection (ILI)
- Data analysis and preliminary results reporting within 24 hours
- Support client in performing line repairs
More than half of the client’s piping segments were thin-walled stainless steel, which increased the complexity of the inspection work. Most ILI technologies are incapable of inspecting stainless tell piping due to its low magnetic potential and the inherent challenges of discriminating pipeline indications in such thin-walled piping (013 inch). The challenge with thin wall piping and ultrasonic inspection
technology is in dealing with the acoustic variations within the near field. Close to the ultrasonic transducer, there are a high degree of fluctuations in the sound intensity due to the constructive and destructive interference of the multiple waves, which originate from the face of the transducer. Due to the acoustic variations within the field, typically referred to as the ‘near field,’ the ability to accurately evaluate flaws in materials when they are positioned within this area is extremely difficult.
Eventually the pressure waves combine to form a relatively uniform front within the medium measured. The area where the ultrasonic beam is more consistent and uniform then spreads out in a pattern originating from the centre of the transducer is called the ‘far field.’ Identifying where the far field starts is the key to determining the optimal detection point as this occurs when flaws are located at the start of the far field. The far field is considered optimum for detection as this is where the sound wave is stable and at its maximum strength. The changeover point between the near field and the far field – commonly referred to as the ‘natural focus’ – can be calculated if the frequency and diameter of the transducer and the speed of sound in the material are known. Applus+ RTD calculated that the frequency of the transducers on the DTI Trekscan tool could be optimised to obtain excellent wall measurement data.
Given Applus+ RTD’s extensive experience in inspecting austenitic thin-walled stainless steel with the previous developments of NDT ultrasonic inspection systems RTD Rotoscan
(automated ultrasonic testing) and NDT3D IWEX
(inverse wave field extrapolation), this knowledge and experience was transferred into the development of the new DTI Trekscan solution. The DTI Trekscan tool performance was validated in the Applus+ RTD test flowloop that was fitted with several SCH-10 SS spool pieces with various machined and OD natural occurring corrosion defects in order to verify the probability of detection, identification and sizing prior to mobilisation to the customer site.
Outcome and lessons learned
The initial inspection run was successfully completed in water utilizing a third part contractor for pumping, storage and water management services. Due to a prolonged mechanical pipeline cleaning process, the water management expense was causing budget overruns and jeopardising the project schedule. Working with the client, Applus+ RTD was able to take advantage of the lightweight design, low drag and low flow design capability of DTI Trekscan by utilising an onsite fire hydrant as the source of water for propelling the tool. All subsequent runs have utilised hydrant water providing significant cost savings as well as yielding shorter project timelines.
During subsequent runs, Applus+ RTD was able to maximise the effectiveness of each DTI inspection by combining multiple pipe segments in a single inspection by looping the segments using a temporary industrial hose. This was a first for DTI Trekscan and provided significant value to the customer in regards to both cost, time and amount of pipeline inspected via a single launch and receive.
Data analysis and final reporting
Automated weld and defect identification and an ultra-low signal to noise ratio allowed for quick and effective discrimination of false calls versus true reportable events within the recorded data set. The result was the preliminary analysis was performed overnight and throughout the next day utilising the company’s global data analysis team providing significant time zone advantages and allowing local final analysis and data review with the client in less than 24 hours. Final reporting was completed within 15 days.
Overview of pipeline corrosion and mechanical damage
When developing a solution for challenging/difficult to inspect applications, it is critical to partner with the customer to understand their time, cost and resource constraints and evaluate the cost benefits of all external and internal non-destructive methods, given that no single technology or technique can be applied in every application.