Page 40: of Offshore Engineer Magazine (Jun/Jul 2015)

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• tests in simulated service conditions. Installation methods and imparting of

Such tests can ensure safe materials high plastic strain • selection while avoiding excessive con- Commissioning and subsequent lay-up servatism in testing that could potentially prior to operation • eliminate good candidate materials. End-of-life condition and potential

Eyebrow Production

During the past two decades, deepwater recovery/abandonment and ultra-deepwater developments have

For existing assets, FFP must be con- driven the need to assess the corrosion- sidered to have con? dence in continued fatigue performance of steel catenary risers integrity if a change in service or life-

Fit for HPHT (SCRs) in mild sour conditions as well as extension is required. the impact of the external seawater envi-

Exova Group’s Stuart Bond he behavior of materials in the Materials sampling ronment with cathodic protection. More presence of hydrogen sulphide In most test methods, it is necessary to recently, the corrosion-fatigue behavior in shows how the company is

T (H S) for sour service has been sample materials to produce test speci- sweet produced ? uids and the effects of 2 working to develop testing studied for nearly 50 years using stan- mens. For tubulars, line pipe and girth lateral buckling have been addressed.

However, in these cases, the vast major- dard tests, which can adequately predict welds, the range of test methods avail- technologies to ensure SURF ity of endurance testing has been per- resistance to degradation via testing in able to assess resistance to degradation components are ? t for HPHT formed under ambient pressure and has laboratory-standard conditions. in sour service is quite wide (listed in and H S service. been limited to maximum test tempera- Today, technology exists to perform ISO15156/NACE MR0175). Therefore, 2 tures of around 80°C. Some endurance both speci? ers and users of the standards testing of wires for ? exibles, plus fatigue must understand the rami? cations of the crack propagation and frequency scan- test technique. Test techniques include ning, has been undertaken at elevated reproducibility, ease of testing and mate- temperature and pressure by Exova. rial sampling, retaining the as-received

Now industry professionals need to surface condition and microstructure, consider how clad systems can be tested sampling from within the wall of the using elevated temperature and pressure. product, relaxation of residual stress,

In addition, high-pressure, high-tempera- relevance to service, and more. These ture (HPHT) developments could further factors in? uence the degree of con? dence drive corrosion-fatigue testing – even for in the results and the extrapolation to components such as downhole tubulars consideration of FFP for the intended and wellhead equipment. service duty.

Factors to consider include:

In? uence of specimen geometry and

Proactive ? tness for purpose (FFP) •

During the initial design phase, mate- extraction upon relevance of the test rials selection for subsea umbilicals, method to service.

risers and ? owlines (SURF) components Uniaxial tensile specimens must

Exova’s Dudley, UK, autoclave facility. can be predicated upon knowledge of be selected from within the body of

Images from Exova suitability from ? eld conditions or, in the material (to allow the machining borderline cases, a desire to test materials of threads) and are fully machined. to optimize selection. Testing is required Therefore, these cannot be used to to qualify materials and weldments for sample the surface microstructure and proactive ? tness for purpose (FFP) for condition. However, this is a reproduc- new developments, which extend the ible geometry that provides con? dence material’s application to higher pressures that there will be little variation between and temperatures. Sometimes tests are specimens in? uencing test performance.

• undertaken early, using non-project spe- Weldments need special consideration.

ci? c material to avoid later dif? culties. The extraction of material from weld-

Aspects to consider include: ments results in a relaxation of the

Mechanical properties and tolerable residual stresses, which can contribute • ? aw sizes for installation to environmentally-assisted cracking.

Material resistance to degradation (e.g. Due to the thermal cycle (development of • corrosion), environmentally assisted the heat affected zone, HAZ), dilution of cracking and corrosion fatigue the weld metal in the root and presence

Operational conditions and changes of heat tint oxide, the microstructure in •

Predicted upset or intermittent weldments differs from the parent mate- • conditions rial. Thus the usual recommendation is

These factors then in? uence the mate- root-intact 4-point bend testing. rial selection, which is based on: It is also necessary to ensure that all

Environmental conditions, mechanical appropriate damage modes are assessed •

Exova’s Houston slow strain properties and compatibility with other in materials selection, including testing rate testing facility.

materials when required. In the latter case, ensure

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