What is HiLo and why should you measure it?
What is HiLo measurement?
HiLo, also called misalignment, refers to the mismatch in height between two pipes lined up for welding. HiLo measurement tools measure the internal and external height difference between the two pipes.
In a pipeline project the HiLo tolerance is set before welding begins and then pipes must be aligned so that they do not exceed this.
Why is measuring HiLo important?
Poor pipe alignment causes weaker welds that are less able to cope with the high fatigue conditions required in oil and gas pipelines. Pipelines with higher quality welds are better equipped to handle increased stress and without risking integrity. Asset lifetime may be increased and safety improved.
Measuring HiLo just before welding confirms the best fit-up selections for critical fatigue-sensitive pipes and reduces the chance of expensive weld-related cut outs. Reducing HiLo is also a key part of ensuring a weld will pass inspection in the QA/QC stages and meet project specifications.
The measuring process
Internal and external HiLo is measured just before pipes are welded together using a measurement gauge.
Measuring HiLo at OMS
OMS offer two HiLo measurement tools – the Open Gap Tool, which measures internal HiLo and the Closed Gap Tool, which measures external HiLo.
The Open Gap Tool has two small blades with a hook on each end. A dial gauge, set to register zero when the blades are of equal length, is pushed into the pipe against the force of a spring to the point at which both blades will go through the gap. The gauge is rotated 90° to allow the hooks to touch the inside of the pipe as the pressure is released. Any mismatch in the blades shows as a positive or negative number on the gauge. The Closed Gap Tool works in a similar way, with two blades pushed into the pipe until both touch the bottom of the J-prep bevel.
Both tools attach to the pipe with a magnetic mount and are easy to use. Accurate to over 0.05mm, OMS HiLo tools have been used by all major welding and pipe-lay companies across the globe to become the industry standard.
Reducing HiLo with SmartFit
OMS SmartFit is a sophisticated software solution that can be used to reduce HiLo on critical projects. To read more about SmartFit click here.
Post-welding inspection
Once welding has taken place, OMS offers an award-winning weld inspection system to provide further assurance that the weld meets the required specifications.
To enquire about OMS HiLo tools or for more information won weld inspection please contact us here.
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Posted 22.12.2020
[5 minute read]
By Paul Eagle, Sales Director