PhD Studentship-(Sponsored by the Non-metallic Innovation Centre (NIC)- Application of diagnostic methods in order to monitor the ageing process and life prediction in polymers.

Details:
Metallic materials have been used for decades for load bearing or containment in various flow line
and wellbore configurations, in oil and gas applications. Some types of parent and welded, steel can
degrade in the presence of fluids containing combinations of oxygen, water, carbon dioxide, hydrogen
sulfide and chloride ions. The corrosion rates of these materials have been established in most cases,
allowing in service lifetime prediction in some oil fields, where the pressure, temperature and fluid
composition is known. In an attempt to mitigate corrosion of metal, some components have been
manufactured from thermoplastic polymers. Generally grades from polyamide, polyvinylidene
fluoride, polyether ether ketones or polyethylene have been used for many years as pressure barriers
or liners in flexible riser, flow lines, jumpers, polymer lined pipes or wellbore tubulars. In water
conveyancing applications or wellbore based tool housings, reinforced thermosets such as epoxy or
bismaleimide have been used for decades. The position of the critical polymeric layer in the hybrid
multi-layered system varies substantially between products.

There is now a pressing need to establish the residual lifetime in polymeric components by in line
monitoring, without interruption of operations processes. Ageing studies on unfilled thermoplastic,
reinforced thermoplastics and also thermosets have established the degradation process that lead to
loss in performance. Essentially the polymeric materials can be altered at a molecular level in the
presence of fluids that can be described by any of;

· a reduction in molecular weight caused by hydrolysis or oxidation
· crosslinking at elevated temperature in the presence of oxygen
· loss of plasticisers or other stabilisers leading to changes in crystallinity and an alteration in
the glass transition temperature
· degradation of tie layer or sizing agents leading to debonding of the resin from the
Reinforcement

The use of thermoplastic materials, due to their better chemical resistance and ease of processing,
have been increased widely in the oil and gas industry. Thermoplastic materials used in piping
applications are normally used as a liner for a host pipe, e.g. Carbon steel, or in a thermoplastic
composite pipes. The purpose of the thermoplastic liner is to provide protection for the metal host
pipe or the reinforcement layer from the hydrocarbons and corrosive elements within the fluid being
transported. However, thermal and chemical degradation of the thermoplastic material occurs over
time while these materials are exposed to the abovementioned fluids and in service condition, leading
to loss of mechanical properties and also allowing the damage of the structural metallic/reinforcing
layer. Subsequently, there is a need to establish a non-destructive method to monitor any change in
the mechanical or barrier properties of the polymer liner over time.

Objective:

The research project will investigate the ageing of limited number of thermoplastic materials due to
chemical (H2S, CO2 and aromatic hydrocarbons), pressure and thermal loadings. The selected materials
will be subjected to series of chemical and thermal conditions, followed by diagnostic analysis in order
to determine the aging of the polymers and potentially their residual life.

Actions and Deliverables during studies:
1) Detailed literature review on the ageing mechanisms associated with the limited number of
common thermoplastics being used in Oil &Gas industry;

2) Selection of materials and shapes of the specimens for the investigation;

3) Effect of number of service parameters on specimens:

a) Chemicals composition of the fluid;
b) Temperature ( thermal effect);

4) Application of diagnostic methods on specimens without and after loading conditions

a) Non-destructive methods:
i. Ultrasonics (changes in velocity, attenuation and frequency responses)
ii. Microwave (changes in response in attenuation and phase in the 1-10GHz range,
possibly up to 60GHz)
iii. Near Infra-Red Spectroscopy
iv. Electrical Impedance Analysis
b) Destructive methods
i. Tensile tests (E, n, local stress at maximum)
ii. Bend tests
iii. Hardness measurements
c) Material composition and structural arrangement
i. electron microscopy
ii. Differential scanning calorimetry
iii. Fourier transform infrared spectroscopy
iv. Gel permeation spectroscopy for molecular weight determination
v. Oxidative induction time

5) Comparison of results in order to select reliable NDE method assessing aging process;

6) A draft design for utilising the selected NDE method in the working condition.

NSIRC is a state-of-the-art postgraduate engineering facility established and managed by structural integrity specialist TWI, working closely with, top UK and International Universities and a number of leading industrial partners.

Candidates should have a relevant degree at 2.1 minimum, or an equivalent overseas degree in Mathematics, Material Science or Mechanical/Chemical Engineering.