The connections play an important role in the technical integrity of the casing string. The casing designer should be aware of the major categories of connections, the different sealing mechanisms used, their strength and the effect of different loads on their performance. All well designed connections form seals when specific make-up requirements are met. Leakage of connections is normally caused by:

  • improper design;
  • failure to meet manufacturing tolerances;
  • damage due to handling;
  • failure to comply with the make-up requirements;
  • loading above the rated capacity or downhole operations.

Structural failure of connections may manifest itself as galling or other deformation of thread or sealing area during make-up, or in the worst case as parting of the connection. Since thread compounds have a direct influence on most of these failure modes, compound selection and how to apply it must be addressed. Protection of the threaded parts and seal area of the connection during transport and use on the rig should also be considered.


Connection types

Connection types

Casing connections should satisfy several functional and operational requirements which are presented in this article.

Functional aspects

  • to provide a leak resistance to internal or external fluid…

Connection Thread compounds

Thread compounds are used for three distinct purposes:
- to prevent corrosion of the connection parts during storage;
- to facilitate the running of connections during make-up/break-out;
- to seal the…

Connections Surface treatments

In order to ensure the functional efficiency of a connection, even after multiple make-up operations, surface treatments are applied to the box, the pin or to both. The surface treatments are applied…

Reliability and structural integrity of connections

This article addresses the possible loads on a connection and its sealing and structural capacity. It should be highlighted that these capacities do not always produce the same value.

1 Imposed loads…

Casing Thread protectors

Before casing joints are installed in a well, they are exposed to a variety of harsh conditions during transport, handling and storage. The threaded pipe ends frequently have to withstand accidental…

Connections Selection and ordering

When selecting a casing connection the actual load on the connection should be compared to the connection's capacity. This is applicable for all types of wells: exploration, appraisal and development…

Connection sealing

Threaded casing connections utilise three basic mechanisms to establish a leak tight joint. These mechanisms are:

  • tapered interference fit thread seal;
  • metal-to-metal seal;
  • resilient seal.

1 Tapered…

Connections Testing and qualification

The general accepted method for the qualification of casing connection designs is, at the moment, the conducting of tests on a number of full scale specimens. The aim of such an investigation is to…