Aluminium Parapet Investigations

 Aluminium Parapet Investigations


Aluminium Parapet Investigations are something that we, often working in conjunction with contractors overseeing Highways England area schemes, have experience in successfully completing.

Aluminium parapet systems are subject to stringent design requirements for impact, it has been observed that in some circumstances posts that have been in use for some time and were subject to vehicle collision exploded on impact.  This has been addressed in the Network Management Manual (NMM) published by Highways England (formerly the Highways Agency) where in Part 3, section 3.7.4 of Version 1, Amendment 8 issued in July 2009, the risk to personnel from localised explosion during drilling/dismantling operations is discussed.  Inspections are required to identify pressure build up in the posts (signs of bulging, seepage of a white fluid, cracking etc.).  The cause of this is a build up of liquid and flammable gas (Hydrogen) within the sealed post as a by-product of the corrosive deterioration of the aluminium.

Works may involve:

  • Visual inspection of the post for signs of damage and also ‘bulging’ of the sidewall which could be a sign of a build up of gasses within. Tapping survey of the post to determine any build up of liquid within.
  • Dimensional survey of the post and rail system present.
  • Ultrasonic thickness measurement of the sidewall of the posts, any loss possibly being attributable to corrosion of the metal.
  • Sampling by drilling of liquids and/or gasses for subsequent laboratory testing.
  • Leaving a small vent hole in the post to prevent future liuid/gas build up.

Liquids and gasses sampled are tested by bulk screening, typically for:

Liquids:-  Aluminium, Calcium, Copper, Potassium, Magnesium, Sodium, Silicon, Chloride, Sulfate, pH

Gas:- Carbon dioxide, Carbon monoxide, Ethane, Hydrogen, Methane, Nitrogen, Oxygen, VOC’s

A written report of the aluminium parapet inspections is provided along with photographic evidence of the condition of the posts and any liquid seepage after drilling.