The objective of this program is to conduct research that will lead to safer, more economical pipeline construction, cost effective mechanised welding and improved on-line quality control. This in turn should lead to reduced danger to the public, reduced pipeline costs and hence reduced greenhouse gas emissions and reduced dependence on decreasingly available skilled welders.

These objectives will be achieved through the completion of the following projects:

In-service welding of high pressure gas pipelines
The aim of this project has been to develop procedures for the safe and effective in-service welding of high pressure, thin walled, high strength steel, gas pipelines. The establishment of guidelines for welding on thin walled high strength steel pipelines will reduce time consuming weld procedure development and enhance the economic expansion of pipeline networks by avoiding the costly and inconvenient option of pipeline decommissioning. The refinement of numerical models and increase in their scientific credibility will provide direct industry benefits and enhance Australian pipeline expertise. The application of advanced numerical process models to determine suitable in-service welding procedures for thin, high strength, gas pipelines is a novel process and is leading to the consideration of alternative welding processes to those conventionally used by the industry.

The two substantial issues during welding on in-service pipelines are the risk of weld failure through cracking and the risk of penetrating the pipe, a problem referred to as burn-through. Controlling the heat input is a major concern.

The project work has developed computerised 3D simulations of in-service welding using a commercial finite element code. A new heat source formulation has been developed which extends the concept of the double ellipsoidal heat source and allows the approximation of weaving and welding angle. A new method of burn-through assessment has been developed which improves existing methods since it accounts for internal pipe pressure and welding direction, which the current method does not do. A 'user database' concept has been developed which may lead to Windows based software that could easily be used to transfer the technology developed in this project into an industrially useful tool.

Experimental studies of in-service welding with low-hydrogen electrodes have been carried out and the numerical predictions have been verified by comparing predictions with measurements made on an operational flow-loop.

Mechanised girth welds for thin walled pipes
During the 98/99 year the GMAW system which was previously found to be viable was further developed and complete circumferential pipe welds were made using solid wire consumables which matched the properties of the X80 pipe material. It was shown that a procedure combining a controlled short circuit transfer root run with a pulsed GMAW fill gave good operating tolerance and satisfactory joint properties. An on-line procedure control and monitoring system was also built and this was evaluated during laboratory trials and during field tests with in service welding. The monitoring hardware/software package has been commercialised and made available via an SME; Emtech Ltd. Work on a welding system design has continued at the University of Adelaide and a novel design concept has been developed; this system will be taken to the prototype stage for evaluation. Work on an integrated control and field welding QA system has commenced with the award of an APA-I studentship to the University of Wollongong.

Electrical resistance welding of high strength linepipe
BHP Oil & Gas in conjunction with BHP Flat Products has developed high strength pipe grades to meet the needs of the Australian pipeline industry which is currently in a mode of rapid expansion. The domestic supply of pipe to the rapidly expanding pipeline network system is currently under threat by imported pipe that is claimed to possess superior quality in terms of weld zone fracture toughness.

To meet the stringent requirements now demanded of pipeline operators the Centre has been working closing with BHP to identify, monitor and control the process parameters known to influence the occurrence of weld line imperfections.

Modified processing parameters and heat treatment conditions in conjunction with on-line welding monitors have resulted in significant improvements in pipe mill yields. This work has been instrumental in the success of BHP O&G securing supply of pipe for the Eastern Gas Pipeline which will run from Longford in Victoria to Sydney. This technology will also benefit lower grade products in terms of overall quality, production rate and ultimately pipe price.

Quality monitoring of automated gas metal arc welding
To ensure acceptable quality of GMA welding for transmission pipelines generally requires costly and time-consuming post weld assessment and non-destructive examination (NDE). A distributed on line monitoring system for a mechanised pipeline girth welding system could be used instead and is currently being developed. Both local area networks and internet technologies are being evaluated for monitoring multi head field pipe welding systems, with a specific emphasis on automated pipe welding systems.

Of crucial importance for the successful application of automated GMAW systems for field pipe welding is that the standoff (contact tip to workpiece distance) remains within a specified tolerance, despite ovality of the pipe. Therefore, this project also investigates on-line standoff estimation and control for this application.

Solidification cracking in high strength cellulosic weld metal
Solidification cracking of steels is composition and cooling rate dependent and can occur in high strength steel weld metals which are being used increasingly for strength matching of high strength low alloy structural steels.

A Gleeble thermomechanical simulator has been used to investigate the susceptibility of high strength cellulosic weld metals to hot cracking. Four different kinds of commercially available weld metals are being studied in the current research. A special sample holder has been constructed in order to achieve cooling rates similar to those experienced in girth welds of steel pipelines. Samples of different weld metals have been heated above the melting point and cooled at different rates. Optical microscopy has been employed to characterise hot cracking of weld metals and to provide guidelines for the conditions under which hot cracking is possible under actual welding conditions.

Fracture risk in pipeline girth welds
The critical assessment of the significance of defects within a pipeline girth weld has cost implications on the production, repair, and inspection of pipelines during construction. Current standards may be too conservative and too demanding with the consequence that benign defects are repaired. This is a significant economic penalty.

Wide plate tension tests have become an acceptable way of establishing the maximum defect length that can be tolerated for a given welding procedure and pipe material combination. This is based on a safe condition being one that promotes plastic deformation within the pipe material before the weld yields. However these tests are difficult to carry out and can cover relatively few weld conditions. In addition there have been relatively few fracture tests on full-scale pipes, so the relationships between plastic behaviour in the wide plate tension test and behaviour of the pipe under service loads is not well established.

This project work is attempting to address this topic by analysis of such plastic behaviour using numerical non-linear, elastic-plastic finite element methods. Simply, numerical models of wide plate tension tests are being compared with similar numerical models of defects in full-size, pipeline girth-welds subjected to simulated in-service loading.

Currently models of wide plate tension tests have been developed and the predicted behaviour compared against test data. The development of full-size pipe models is in progress.

Defect acceptance levels in high strength pipeline girth welds
Previous research on this subject by the Centre has addressed the critical issues affecting defect acceptance levels in high strength pipeline girth welds and there is now evidence to support extension of the current generalised fitness for purpose based defect acceptance level in Australian Standard AS2885.2. This has the potential to increase the economic benefits to a larger number of pipeline construction projects by avoiding unnecessary repairs and costly cut-outs. However, the work also identified that current cellulosic consumables can considerably undermatch both X70 and X80 grade pipe and that conventional workmanship standards may not be appropriate for thin walled high strength pipelines. These projects have developed the expertise and the appropriate experimental techniques to determine appropriate workmanship defect acceptance limits for the pipeline industry for the safe and economic operation of petroleum pipelines in Australia.

Pipeline hydrostatic testing
Mathematical models have been developed to gain a more fundamental understanding of pressure/temperature relationships in buried pipelines during hydrostatic leak testing for Australian gas pipeline conditions. Fibre-optic methods are being developed for pipeline leak testing.

Recommendations have been made for temperature stabilisation criteria, after the test section has been filled and pressurised, as a function of test water temperature, ground temperature and ambient temperature. Additionally, recommendations have been made for methods of temperature measurement of buried pipelines to allow correlation with pressure changes.

The mathematical modelling should shortly be completed and field trials are planned for the fibre-optic instrumentation.

Pipeline resistance to external interference
External or mechanical interference is the major cause of failure of onshore pipelines. The latest edition of the Australian Standard for gas and liquid petroleum pipelines AS2885.1-1997 includes the requirement to prove sufficient resistance to external penetration using risk assessment techniques. However, at present there are limited experimental and analytical data on the consequences of external interference. The aim of this project is to generate guidance on the probable damage resulting from typical external interference threats on Australian gas pipelines. Work to date has concentrated on collecting available literature on experimental studies of pipeline denting, gouging and puncture, as well as data on mechanical equipment types and sizes in Australia.

Stress in girth welds
This project is addressed to the solution of residual stresses during the combined processes of root-pass welding, lifting and lowering and hot capping. Non-linear, elastic plastic thermal-mechanical models will be used. This stress development is expected to have an important influence on hydrogen cracking.

Weld repair in gas pipelines
Advanced numerical 3-D models will be used to directly calculate the possibility of cracking or burn through during weld repair. The systematic use of weld sequence will be used to optimise a temper-bead technique for the control of post-weld hardness.

Pipeline awareness
A literature survey will be conducted and a database developed of procedural methods used to inform people of the location of pipelines and of the serious consequences of damage. Sociological techniques will be used to measure the effectiveness of these methods.

Pipeline backfill specifications
The specifications will be reviewed and a set of specifications will be developed that will meet the need of pipeline designers and operators taking into account all soil and rock types that may be encountered on pipeline routes.