API RP 1110:2007 pdf download

API RP 1110:2007 pdf download.Pressure Testing of Steel Pipelines for the Transportation of Gas,
Petroleum Gas, Hazardous Liquids,Highly Volatile Liquids or Carbon Dioxide.
I. Identification ofjoint Connections within the test section:
i. Consider exposing all threaded, bolted or flanged fittings within thc test segment prior to the test for visual inspection during thc test.
ii. Consider replacing any gaskets within the test section prior to conducting the pressure test.
5.1.10 Target Test Pressure and Pressure Test Duration
Detennination of the target test pressure of a pipe segment should take the following into considenition
a. Elevation ditTerences within the test section.
b. Current operating pressure limit of the pipe segment.
c. Past hydrostatic test pressures (mill test pressure, if known).
d. Desired operating pressure limit for each point within the pipeline segment.
c. Maximum allowable piping stress levels to be created by the pressure test.
f t.owcst ANSI appurtenance rating.
g. Past failure history (in-service and pressure test).
h. Presence of people. stnictures or environmentally sensitive areas within the test section boundaries that would possible be
impacted by a test failure.
i. Mainline valve locations.
j. Results of past in-line inspection and other assessments.
k. Evaluation of mill test data.
Testing to higher pressures will eliminate some flaws that would survive if tested at lower pressures. The test duration at thc maximum test pressure should be designed to minimize any potential flaw growth. The pressure test subjects the pipe to a high level of stress with the goal of removing, through failure, any flaws that are greater than the critical size for the stress level imposed. With an increased test pressure ratio, surviving flaws arc smaller, the safety factor is greater and the time to failure and reassessment intervals for time dependent flaws is greater (see Figure 1).
Figure I illustrates the relationship between flaw depth (a) divided by pipeline wall thickness (t), flaw length, and test pressure for a typical pipeline. The shaded areas represent the population of flaws eliminated by a strength pressure test pink) and a spike pressure test (green). Relatively larger flaws remain afler a strength pressure test conducted at 90% of the SMYS than the spike pressure test conducted at 100% SMYS. Larger flaws do not have to propagate as far or deep as smaller flaws to reach the critical length/depth where they are likely to fail at 79.2% SMYS (72% SMYS plus 10% over-pressure protection set point).
For example, the required flaw extension to failure at 79.2% SMYS (72% SMYS plus 10% over-pressure protection set point) after a spike pressure test for a 6-itt. long (L 6 in.). 20% deep flaw is illustrated by the blue lines connecting points “A” and “C’ ( AC 7.0 in.; u/i=0.2). This is 1.66 (AC/BC ‘ 7)4.2 1.66) times the extension required for failure for the same depth flaw remaining afler a strength pressure test. The required flaw depth propagation for 79.2% SMYS (72% SMYS plus 10% over-pressure protection set point> atIer a spike pressure test for a 6-in long, 20% deep flaw is illustrated by the red lines connecting points “A” and ‘E ( 0.26). This is 1.86 (AFJDE = 0.2610.14 = 1.86) times the growth required for the same length flaw to extend to failure 79.2% SMYS (72/a SMYS plus 10% over-pressure protection set point) after a strength pressure test.
In this case, the flaw growth required to fail at 79.2% SMYS (72% SMYS plus 10% over-pressure protection set point) is increased by 66% — 6% by adding a short duration pressure spike to the pressure test (spike pressure test). Fracture mechanics principles were used to generate Figure I. The characteristics of the pipeline to be pressure tested must be evaluated in the same manner to determine the additional benefit derived from a spike pressure test.
Repeated tests within the same section should be avoided since restressing pipe and pipeline components may cause flaws to grow to unexpected lengths without failing. Repeated tsls may lead to a lower pressure where subsequent failures may occur (pressure reversal). There should be a balance between test duration, test pressure and the probability of repeated failures as opposed to how man test failures the operator is willing to tolerate betbre reducing the lest pressure and ultimately the operating pressure limit.