Assignment – 1
For
Please Click Below mention Link and Get this Solution
Fundamentals
of Petroleum Refining
Section A
Write short notes
on any four of the following
1.
Crude Oil Distillation Unit
2.
Octane Number
3.
Polypropylene
4.
Amine Treating Unit (ATU)
5.
Oxidation Stability
Section B (30 marks)
(Attempt any three)
1.
Discuss the important
milestones in Indian Refining Industry.
2.
“Crude
Assay is the determination of properties of various fractions of crude oil.”
Explain.
3.
Hydrogen
is produced commercially using various technologies. Explain these
technologies.
4.
What
are the major offsite functions in a Refinery?
Section C (50 marks)
(Attempt all questions. Every question carries 10 marks)
Read the case “Seam Weld failure in petroleum
pipeline” and answer the following questions:
Case Study: Seam Weld failure in petroleum pipeline
There
are more than 2.5 million miles of oil and gas pipelines in the United States.
These pipelines typically contain longitudinal seam welds in each pipe joint
and girth welds that connect the individual joints to form the pipeline. Both
types of welds are prone to failure from time independent and/or time dependent
failure mechanisms.
Many
failure investigations focus on the immediate failure cause; i.e., for metals,
the metallurgical or technical aspects of the failure.
While
some smaller diameter pipelines are seamless, most pipelines are manufactured
by forming flat plate or skelp into a tubular form and completing a
longitudinal seam weld. Both submerged arc welding and autogenous welding
processes are used for weld completion.
Submerged
arc welded line pipe is manufactured by first forming a flat plate or skelp
into a tubular shape (can) in a set of presses, followed by weld completion.
Prior to forming the can, the edges are typically bevelled. Historically,
single submerged arc welding (SSAW) and double submerged arc welded (DSAW)
processes have been used but, currently, the DSAW process is the only submerged
arc welding process that is approved in API 5L. In SSAW line pipe, the edges
are joined by a single pass submerged arc weld made from the outside surface
onto a backing shoe located at the ID surface. DSAW line pipe is formed in a
similar manner except one pass is made from the OD surface followed by a pass
from the ID surface, or vice versa. Filler weld material is used in both
processes. One variation of this process is used to produced spiral welded DSAW
line pipe; in which skelp is helically wound and welded to produce a spiral
weld.
Historically,
there have been several different autogenous welding processes for longitudinal
seam welds including furnace lap welding, furnace butt welding, electric flash
welding (EFW) and electric resistance welding (ERW). ERW currently is the
dominant autogenous welding process for pipe manufacturing. ERW line pipe is
manufactured by forming plate or skelp into a tubular shape and heating the two
adjoining edges with electric current and forcing them together mechanically.
An autogenous bond is formed between the molten edges. Upset material at the
weld is trimmed on the OD and ID surfaces.
Various
types of defects can be produced in these welds and the defects typically are
unique to the specific welding procedure. Some of these defects are too small
to be detected in the mill and are never an integrity problem for the
pipelines. Other defects that are not detected at the mill can fail during the
initial hydrostatic test of a pipeline, or grow in service by fatigue, stress
corrosion cracking, or other mechanisms, resulting in a service leak or
failure. Because of differences in the metallurgy at the weld and the base
metal of the pipe, the welds can also be prone to environmentally induced
failure mechanisms such as preferential corrosion.
This
case study describes a rupture of seam weld during a hydrostatic pressure test.
The pipeline that failed was comprised of 16-inch diameter by 0.312-inch wall
thickness, API 5L X52 line pipe that contained an ERW longitudinal seam. The
pipeline transported refined petroleum products. The maximum operating pressure
(MOP) on this line segment was 1,408 psig, which corresponds to 69.4% of the
specified minimum yield strength (SMYS). The failure occurred during initial
pressurization at a test pressure of 1,390 psig, which corresponds to 98.7% of
the MOP and 68.5% of the SMYS. The normal operating pressure at the failure
location ranged from 1,000 to 1,100 psig (71.0 to 78.1% of MOP).
The
pipeline was installed in 1965 and was externally coated with coal tar. The
coating was not intact near the failure. The pipeline had an impressed current
cathodic protection system that was commissioned around 1965. This pipeline
segment was previously hydrostatically tested in the fall of 1965. The
hydrostatic test lasted 24 hours and the maximum pressure was 1,760 psig (125%
of MOP and 86.8% of SMYS).
The
pipe section was visually examined and photographed in the as-received
condition. Transverse base metal and cross weld samples were removed from the
pipe section for mechanical testing. Samples for chemical analysis of the steel
were removed from the base metal. Magnetic particle inspection (MPI) was
performed where the coating was removed to identify defects at or near the seam
weld. Transverse metallographic samples were removed from the seam, at and away
from the failure origin. The samples were mounted, polished, and light
photomicrographs were taken to examine the morphology and steel microstructure.
Samples were removed from the failure origin to analyze the morphology of the
fracture surface in the scanning electron microscope.
The
results of the analysis indicated that the rupture initiated at an ID connected
pre-existing hook crack. This and all hook cracks are slightly offset from the
bond line of the ERW seam. No evidence of in-service growth by fatigue was
found, although the quality of the fractography was poor as a result of
corrosion of the fracture surfaces that occurred after the rupture. The tensile
properties of the line pipe steel and the steel chemistry were typical of the
vintage and grade and met the API 5L specifications in place at the time of
manufacture. The microstructure and Charpy toughness properties of the steel
also were typical for the vintage and grade.
Questions:
1.
What could be the immediate
failure causes for petroleum pipeline?
2.
Write a short note on submerged
arc welded line pipe.
3.
Describe the composition and
structure of failed Seam Weld pipeline.
4.
Explain the various autogenous
welding processes for longitudinal seam welds.
5.
Analyze the conclusion part of
the case study.
No comments :
Post a Comment