Case study

Sector: Oil and Gas

Objective: Define a minimum allowable thickness by the use of finite element analysis (FEA) and codified procedures.

Client benefits: TWI's analyses allowed the client to make a strategic decision to continue operating the boiler safely for another year before retirement.

Project Background: Inspections had discovered considerable material loss on one side of the tubesheet in a boiler, which had been designed originally as a 'pierced dished head'. The design thickness of the tubesheet in the as-built condition was such that a certain amount of material loss could be acceptable. The aim of the work was to quantify the effect of reduced thickness on stresses in the tubesheet by the use of finite element methods, and to define a minimum allowable tubesheet thickness on the basis of allowable stress intensity criteria in codified procedures.

Solution: Using FEA, stress intensity in the most severely stressed regions was assessed against the allowable stress intensity criteria prescribed in the appropriate codified procedures. Acceptable tubesheet geometry profiles that satisfied the allowable stress intensity criteria were defined, enabling the company to make an informed strategic decision on whether or not to shut the boiler.

For more information please contact: nmo@twi.co.uk