API TR 17TR2:2003 pdf download
API TR 17TR2:2003 pdf download.The Ageing of PA-11 in Flexible Pipes.
4 Field Monitoring of PA-il
Section 13.21 of APi RP l7W3, and other international guidelines’9t, call for the implementation of a risk based inspection & monitoring strategy for all flexible pipes. Some outline guidance specific to polymers is currently given in 13.43 and 13.4.4. and this is expanded in the sections which 10110W hew.
4.1 METHODS OF FIELD MONITORING
I-or PA-Il pressure sheaths. monitoring options are either passis i.e., coupons of PA-Il immersed in flowing stream for removal at regubr intervals API RP 17B section 13.4.3). or ti.” dwtric sensing (API liP l7B section 13.4.4).
Llnder the passive options, it is possible to consinici flanged spook to accommodate a number of samples held flush with the pipe LI). This has the advantage of single sided exposure of the material. but access is diflicult. The alternative optiofl is to employ a standard access fitting, with either flush coupons or a ladder rack type coupon holder. This has the advantage of simpler access using standard equipment. commonly accommodating six in ten sample.. on a single probe. all exposed from all sides. A flush coupon exposes a yip limited amount of material. but has the advantage of single sided exposure of a thickness equivaLent to that used in the flexible pipe. In all cases. coupons should be manufactored [mm material taken from the same manufacturing run, with baseline properties characterised. Small sample analysis techniques are asaibble — typically, CIV measurement requires approximately Ig of materiaL Larger samples for mechanical testing have also been used by some operators.
The only current ‘active” on-line option is the WEMS iFrequency I)cpcndcnl Elcctm-Magncuc Sensing) sensor FIWMS measurements can be correlated to changes in mechanical properties, such as elongation at break. It has bcen thowis that while mechanical propcrhes change slowly with time until relatively close to failure and have large scatter, electrical measurements change right hum the start of exposure.
Details of the pok-mer monitonhig equipment curwntly deployed offshore can be obtained through commereial sources.
4.2 IMPLEMENTATiON OF MONITORING STRATEGY
lithe monitoring strategy demands inspection of the P-s’ II pressure sheath, as a result of the forecast operational condiDons, the anticipated service life, and a risk assessment, it is normal to employ a combination of methods,
The selection of risers, Ilowlines and jumpers to be monitored and the schedule for data collection, including coupon retrieval, is made through detailed consideration of layout. design conditions, and pipe criticality, as part of the risk assessment.
A.1 lntroduction
The ageing of thermoplastics and the consequent loss ofmaterials’ properties are always complicated phenomenabecause of the superposition of several effccts.Errors in theprecise definition of the real life ageing conditions can easilylead to false conclusions.
In the case of PA-11 three main agcing processes havebeen identified for the case of ageing in oilfield flexiblepipes(l,2,3.4,5. 6):
Structural changes due to annealing upon heating;Swelling by oil components and water uptake as well asplasticiser loss;
Loss of molecular weight due to a chemical reactionwith watcr, i.e.. hydrolysis.
In oilfield flexible pipes there is an absence of oxygen, andtherefore,hydrolysis is clearly established as the main mech-anism for molocular weight loss. Moreover，as molecularweight goes down,the performance of PA-1l is eventuallyaffected, in particular elongation at break or impact resistance(see also Appendix 6).There is wide expericnce within poly-mer science of the concept that material toughness is lost withdecreasing molecular weight.
