Lecture 2 - Key Definitions & Boxed Equations

Question 1

What is a Drop Weight Tear Test (DWTT) and how is it used to define toughness levels?

Answer 1

A DWTT is a material characterisation test aimed at avoiding brittle fracture and ensuring crack arrest in pipelines. It defines a specification below which brittle fracture propagation cannot occur.

Question 2

Define Fracture

Answer 2

The cracking or braking of a hard material.

Question 3

Define Gas decompression

Answer 3

A phenomenon that often occurs when high-pressure gas molecules migrate into an elastomer at a compressed state

Question 4

Define Weld-ability

Answer 4

The ability of the pipe or fitting to be welded using
welding procedures which are economic for site pipeline construction, without the formation of cracking or excessive hardness.

Question 5

Define Weld

Answer 5

Join together (metal parts) by heating the surfaces to the point of melting with a blowpipe, electric arc, or other means, and uniting them by pressing, hammering etc.

Question 6

Define HAZ (Heat Affected Zone)

Answer 6

The heat affected zone (HAZ) is the area of base material, either a metal or a thermoplastic, which is not melted but has had its micro-structure and properties altered by welding or heat intensive cutting operations.

Question 7

Define Cracking

Answer 7

Cracking is the process whereby complex organic molecules are broken down into simpler molecules by the breaking of carbon-carbon bonds in the precursors.

Question 8

Describe the Charpy test and indicate how it is used in the specification of toughness for pipeline materials?

Answer 8

The Charpy Test determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given material’s notch toughness and acts as a tool to study temperature-dependent ductile-brittle transition.