Pipeline Inspection at Petronet, South Africa

Introduction
Petronet, a local company that transports natural gas through underground pipelines across South Africa, had approached MA2K Testing Labs to conduct an investigation on a leakage on the pipeline, which was found during a random leak inspection. The Pipeline operates from Johannesburg to Potchefstroom. Upon inspection a joint was singled out as being a major source of leakage. The affected area was joined using a butt weld and reinforced with a clamp. This section was dissected and inspection revealed that the leakage was due to incomplete fusion in the weld which initiated the formation of hook cracks and cavities in the parent material directly adjacent to the weld. External stresses from the environment may have accelerated the growth of the cavities and cracks yet the clamp increased the strength of the joint aiding in the prevention of any accelerated growths of the defects.
As a short term solution it is advised to replace the damaged section with a new pipe. It must be correctly welded of the same material and as an added precaution to weld an additional sleeve over the newly joined and welded section.

As a long term solution it is advised to replace the entire pipeline with a new combination of materials.
1. Background
Petronet, a leading company in South Africa which transports natural gas through underground pipelines conducted a random leak inspection survey on one of their pipelines operating from Johannesburg to Potchefstroom, and it was discovered that there was a gas leak at the specific joint. The pipe carries natural gas and it is imperative that the leak should be fixed, due to the volatile nature of gas as well as the loss of resource, in turn profits. The systems comprised of numerous seamless pipes and connected using a butt weld; these joints were reinforced by clamps bolted on.
MA2K Testing Labs had been approached by Petronet, to inspect the leakage and was employed to identify the true cause of failure and as well as make many suitable recommendations for the repair and prevention of malfunction of the joint. The pipeline was effective since the 20th February 1995; this put the pipeline age in the region of 15 years.
Figure 2.1 (Below) was taken on site
2. Description
The defective section of the pipe, including the clamp was then marked, cut out and removed from the site for further inspection and analysis. The inspection and analysis was carried out in MA2K Testing Labs in Durban.
Two grade A 106 GR.B SCH40 seamless pipes with outside diameters of 168.3mm and wall thickness of 9mm were butt welded end to end. A butt weld consists of the two pipes heated to a proper fusion temperature then joined by means of force. The joint was further secured by a clamp. The operating internal gas pressure was 2620 kPa (380 psi).
Chemical composition of the pipe:
Element
C
Si
Mn
P
S
Cr
Mo
Cu
Ni
V
%
? 0.30
? 0.10
0.291.06
?0.035
?0.035
?0.40
?0.15
?0.40
?0.40
?0.08
3. Possibilities Of Failure