Stress Corrosion Cracking on Welding of Offshore Structure

The objective of this research is to study on Stress Corrosion Cracking on welding of
offshore structure. Offshore structure such as topside will have deflections at the
joint due to a combination of load on the decks. The deflections result tensile stress
on the structure. The tensile stress and residual stress from welding process of the
structure leads to occurrence of Stress Corrosion Cracking.
The scopes of study covers (a) conduct Stress Corrosion Cracking Tests using Bolt
Loaded Double Beam Test, (b) conduct corrosion experiment with the affect of
offshore environment which seawater with pH between 7.5 to 8.0 and temperature of
35°C and (c) examine Stress Corrosion Cracking for material A516 grade 70 with
Shielded Metal Arc Welding (SMAW).
The offshore welding samples were gathered from the fabricator and the samples
were used for testing and experimental works for this project. The sample inspected
by using Liquid Penetrant Inspection to detect any discontinuities of the weld before
any test conducted. The samples then were setup for Bolt Loaded Double Beam
Testing to study the behavior of SCC. With these setup, the samples were examined
under offshore condition in Salt Fog Corrosion Chamber for two weeks (336 hours).
The losses in mass of the samples recorded to calculate the Corrosion Rate. The
characteristics of the sample’s microstructure were studied by using Optical
Microscopy.
It was found that Stress Corrosion Cracking initiated and propagated in the sample
when the deflections of the sample were higher than the design maximum allowable
deflection of the joint of 37.17mm/5000mm length. There are two types of SCC
present in the samples, which are Intergranular and Transgranular SCC. The
presence of SCC increases the Corrosion Rate