Failure in the primary water loop of a power plant reactor:

A $304$ stainless steel pipe $(10$ inch diameter and wall thickness of $0\mathrm{.}8$ inch$)$ which had

served as a part of the primary loop of a power plant reactor was found to have

several circumferential cracks $1$ to $2$ inch long. Two of these cracks which penetrated

the pipe wall were responsible for leaks detected in a hydrostatic test performed

during a general inspection after three years of service. Primary inspection showed

that the cracks were mainly located adjacent to weld lines and in the heat affected

zone. Cracks were mainly branched and intergranular in nature.

Analysis of the pipe showed the chemical composition matched normal $304$ stainless

steel $(18\%Cr+8\mathrm{.}0\%Ni).$ Properties of $304$ stainless steel:

$E=27\mathrm{.}5{10}^6$psi, $YS80$ksi, $TS105$ksi, and CTE$=6{10}^{-6}i\frac{n}{i}nC.$

Fatigue strength of $40\mathrm{.}0$ksi at ${10}^6$ cycles.

The water in the heat exchanger was of sufficient purity that corrosion had not been

anticipated. The water conditions were as follows:

Temperature was cycling between $45C$ to $245C$ about $60$ times a day.

Pressure: $1200$ psi, pH $8-9,$ Chloride content

Electrical conductivity $<mn\; id="EditorElement\_906638">0</mn><mn\; id="EditorElement\_906639">.</mn><mn\; id="EditorElement\_906640">4</mn><mtext\; id="EditorElement\_906642"></mtext><mi\; id="EditorElement\_906643">o</mi><mi\; id="EditorElement\_906645">h</mi><mfrac\; id="EditorElement\_906650"><mrow\; id="EditorElement\_906646"><mi\; id="EditorElement\_906647">m</mi></mrow><mrow\; id="EditorElement\_906648"><mi\; id="EditorElement\_906649">c</mi></mrow></mfrac><mi\; id="EditorElement\_906652">m</mi>$

a$.$ Based on the predicated life for this system, evaluate its performance

b$.$ Explain the primary cause of these crackings.

c$.$ Discuss your corrective measures to increase the life of these piping systems.