Engineering News

Thursday, 28 June 2018

Advances in technology make safer pressure vessels

Advances in technology make safer pressure vessels

When it comes to safety, there is no room for error in pressure vessel design and construction.

The dangers created by using pressure vessels and the potential loss of life have been heavily reduced by the consistent use of the American Society of Mechanical Engineers’ (ASME) Boiler and Pressure Vessel Code (BPVC) across the globe.

The latest edition of the BPVC, published just last year, includes new processes and procedures to further improve safety in the design and fabrication of pressure vessels.

Engineering consultant and ASME facilitator from the USA, John P Swezy Jr. says the Code is continually updated to reflect advances in technology and maintain safety in a constantly changing world.

 “Many of the changes are subtle in nature but significant in their impact”, Mr Swezy Jr said.

“For example, toughness rules, which address brittle fracture considerations, have been updated in response to advances in fracture mechanics and understanding material properties.

“Forged carbon steel flanges are now required to be normalised after forging in order to be eligible for exemptions from impact testing, and flanges which have not been normalised are now assigned to a lower toughness category.

“This change may require manufacturers to adjust their purchasing procedures to optimise their use of forged carbon steel flanges.”

Specific text has also been updated to accurately communicate the intent of the Code.

The rules for the assignment of weld joint efficiencies were discovered to be implying that they were only applicable to arc or gas welding processes. Modern methods such as laser beam, electron beam, and friction stir welding were thought not to be included, causing confusion.

“When we discover the wording in the Code is ambiguous, we update it to improve clarity and interpretation”, Mr Swezy Jr said.

“The code words have been revised to address weld joint efficiency assignments for all welding processes, and to also call attention to special situations where alternative rules apply.”

Mr Swezy Jr believes that training sessions can help users understand these nuances and subtleties in the text of the Code.

 “Training sessions are an essential element in helping engineers and technicians understand how the Code should be interpreted and applied effectively”, Mr Swezy Jr said.

“Expert facilitators, who have extensively used the Code, can help students gain these insights over a shorter time frame.”

The ASME BPVC committee have discovered that older fabrication processes detailed in previous editions of the Code do no align with modern day methodologies.

“For example, the development of micro-alloyed and creep strength enhanced ferritic steels has created a need for more detailed preheat and postweld heat treatment rules and procedures”, Mr Swezy Jr said.

 “The updated rules will ensure these materials maintain their desired properties after welding operations.”

A major focus for the committee is to identify and incorporate new technologies and processes that enhance productivity and product safety. An emerging technology in the non-destructive examination (NDE) of pressure vessel weld joints is the use of ultrasonic examination (UT).

 “There is a growing tendency to use UT in lieu of radiographic examination (RT)…”, Mr Swezy Jr said.

 “UT is much more capable of detecting subsurface flaws, with a greater accuracy in determining size and orientation to provide more detailed characterisations of their nature.  

“This method also eliminates radiation hazards and the need to handle harsh chemicals.

“I anticipate it to be the predominant NDE method of choice within five years.”

The BPVC continues to evolve with the committee currently preparing the 2019 edition.

Mr Swezy Jr will be in Australia to facilitate the ASME training course on the Boiler and Pressure Vessel Code Section VIII – Rules for Construction of Pressure Vessels Division 1, Design and Fabrication of Pressure Vessels, in August.