Annulus Pressure Relief System

The Annulus Pressure Relief System (also known as the B-Annulus Relief System) was developed to tackle the problem of B-annulus pressure build-up due to thermal expansion during well start-up.


The Annulus Pressure Relief System (also known as the B-Annulus Relief System) was developed from TCO's Chemical Injection System product line. The product is approved as an ISO 14998 V0 barrier, and features check valves and an internal integrated filtration system. 

The Annulus Pressure Relief System makes the B-annulus pressure independent of the downstream back pressure in the A-annulus, provided that the pressure in the B-annulus is greater than that in the A-annulus. The system ensures an independent operation in which the pressure that is bled off is not a function of the downstream pressure being bled into. 

Conventional approaches constantly relieve pressure as the B-annulus pressure "tracks" the A-annulus pressure. Such constant pressure relief reduces the life of the well, risks barrier integrity and alters the supporting pressure both inside and outside of the casing.

TCO's patented system only bleeds off the pressure that is necessary to hold and maintain a safe, pre-determined B-annulus pressure. The device will only flow when the B-annulus pressure reaches the pre-set relief pressure, regardless of the varying A-annulus pressure. This unique feature means that the system will not constantly flow throughout its life. The device provides a safe and reliable long-term V0 barrier, and operates "on-demand" only when required.

Features and Benefits

  • Fixed B-annulus pressure
  • Stable pressure support from annulus
  • Prevents casing collapse due to pressure build-up in annulus
  • Prevents casing burst due to loss of pressure support in annulus
  • Quick and simple installation as integral part of casing string
  • Bleeds off pressure from annulus automatically
  • One-way communication from B-annulus to A-annulus
  • Approved ISO 14998 V0 gas-tight barrier from A-annulus to B-annulus
  • Enables controllable bleed-down of annulus pressure
  • Controls pressure during start-up of new HT wells without risking further communication from A-annulus to B-annulus     


  • Subsea wells with no access to annulus
  • Wells exposed to thermal expansion of closed fluid volume (HPHT wells) in annulus
  • Wells with annulus monitoring
  • To replace conventional approach of using burst disks between A-annulus and B-annulus
  • To replace use of crushable foam on inner casing
  • Wells with a desired pre-set annulus max. pressure