InstrEng Instrumentation Engineering

Safety Relief Valve Material Selection

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<span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">An important factor in selecting the correct Safety Relief Valve is choosing the correct materials for the application. It is obviously impossible to cover all possible applications, but we will provide some general guidelines here.</span><br />
<br style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;" />
<span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;"><b>Sour gas applications:</b> Here, NACE recommendations should be followed. Most wrought grades are acceptable to NACE. Therefore, in general, duplex valves with bar stock nozzles and discs will meet NACE requirements. Some limited cast grades will generally comply also:</span><br />
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<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">ASTM A890 CE3MN UNS J93404</span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">ASME SA 351 CD3MWCuN UNS J93380</span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">ASME SA 351 CE8MN UNS J93380</span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">Z 6 CNDU 28.08 M, NF A 320-55 at 17 HRC MAX</span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">ASTM A351 CK3MCUN (6Mo)</span></li>
</ul>
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<span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">High -temperature applications (>530°C): As a general rule, a bellows should be used so that the spring gets protected from heat and does not shift its characteristics during eventual temperature cycles.</span></div>
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<span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">For body, bonnet and cap, up to 815 ° C cast materials can still safely be used : ASME SA 351 CF8M with a minimum 0.04% carbon content and maximum 8% ferrite content. In any case, full-rated and integral castings are recommended. Alternatives are:</span><br />
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<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">ASME SA 351 CF8 SAME (with same chemical restrictions as CF8M)</span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">ASME SA 217 WC6 (up to maximum 593 ° C)</span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">ASME SA 217 WC9 (up to maximum 593 ° C)</span></li>
</ul>
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<span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">Wrought materials can also be used up to 815 ° C: ASME SA 479 Grade 316H with a carbon content between 0.04% and 10%. Alternatives are:</span><br />
<ul style="text-align: left;">
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">ASME SA 479 Grade 304H (same chemical restrictions as 316H)</span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;"> ASME SA 479 Grade 347H (same chemical restrictions as 316H)</span></li>
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<span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">For the temperature range 530 ° C to 815 ° C, the following precautions should also be taken into consideration:</span><br />
<ul style="text-align: left;">
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">Recommended bolting material: ASME SA 193 Grade B8 Class 2/ASME SA 194 Grade 8 – strain hardened. </span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">Recommended bellows material: INCONEL 625 Grade 2 (LCF) – annealed after forming or HAYNES ALLOY 230. ASTM B435 UNS N06230 is preferred above 650 ° C but is rather expensive. </span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">Recommended spring material: INCONEL X750. Above 232 ° C, 316SS springs should no longer be used. INCONEL X750 or chrome-plated springs should be considered. Note that cadmium plating used in the past is no longer allowed. </span></li>
<li><span style="background-color: #f6f8f9; color: #545454; font-family: 'Open Sans', Arial, sans-serif; font-size: 13.333333969116211px; line-height: 18.488887786865234px;">Recommended gasket material: 316 STAINLESS STEEL.</span></li>
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Instrumentation Inspection and Quality Control Questioner

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1)<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is QA/QC?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> QA/QC means Quality assurance/Quality control the purpose of this (QA/QC) is to establish the sequence of requirement for the quality of material quality of works its inspection and records.</div>
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2)<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is the basic responsibilities of a QA/QC personal ?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> To ensure execution of works and comply fully as per standard and approved speck.</div>
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3)<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What are QA/QC’s ITP’s and QCP? Give a brief?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> ITP: This is procedure informs about the kinds of quality check (surveillance inspection witness or hold points) means quality of works is being done in proper sequences.</div>
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QCP: This is procedure addresses the activities and requirement in details.</div>
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4) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is NCR? Why does it need for a QA/QC personal?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> NCR means  Non-Compliance Report, QA/QC personal has reserve the right issue a warning of the contractor doesn’t comply or violate with the standard procedure.</div>
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5) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What are general work procedure (WP)?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> The. general sequence of activities will be as follows;</div>
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<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Receiving Drawing and documents.</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Reproduction of Drawing</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Issuing of Drawing to site</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">New issuing New revision</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Shredding of Drawings</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Redlining Drawings</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Transmittal of redlines to client (As-built).</li>
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6) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is ISO? Explain some of its standards?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> ISO means international standard organization some of them are as below;</div>
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ISO;9001, ISO;9002, ISO,9003 etc.</div>
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7) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What are the standard height to install the instruments?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Standard height to install the instruments is 1.4 meter but it can very less or more as per locations convenience.</div>
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8) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is loop check?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> To ensure that the system wiring from field to control console functioning fine.</div>
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9) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is different between open and close loop ?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Open loop: A loop system which operates direct without any feedback and it generates the output in response to an input signal.</div>
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Close Loop: A loop system which uses measurement of the output signal through feedback and a comparison with the desired output to generate and error signal that is applied to the actuator.</div>
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10) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What are inspection points for a cable tray installation.</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Material check as per approved spec, size and type, trays hook-up, proper distance structure, tray to tray i.e. power/control/and signal/low voltage and high voltage , support  fixed strongly not shaking.</div>
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11)<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;"> what are inspection point for field instruments with impulse tubing?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Materials inspection as per approved spec material, type and size installation as per hook-up, check line route to avoid any obstruction check tube support, compression  fitting of ferrules, and then pressure test (hydrostatic test) shall be done.</div>
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12) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What are inspection points for cable laying.</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> material inspection as per approved materials, type and size, meggering, cable routing drawing, completion of cable route (tray conduit or trench etc) and cable numbering tags, cable bending, use of proper tools and equipment for cable pulling.</div>
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13) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What are inspection points for junction box and Marshalling cabinets.</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Material inspection, type, size as per approved specification, installation hook-up</div>
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For frame, bracket or stands, fixed properly means shaking free, name plate and tag no.</div>
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14) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">how do you determine the correct installation of flow orifice?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> The orifice data (tag) shall be punched in the up stream of orifice , the data (tag) side shall be in the upstream  of flow direction.</div>
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15) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Explain why shield of signal cable is not earthed on both sides?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> To avoid the current noise (resonance).</div>
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16) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is final RFI? When it shall be raised up?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> When the QA/QC department of contractor is satisfied that the work detailed in the construction RFI is completed, then request shall be submitted for inspection to the client QA/QC department.</div>
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17) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What are the required documents for an inspection?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Following are the required documents for an inspection;</div>
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<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">RFI (Request for inspection)</li>
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<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">PP for location (pipe plan)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Wiring diagram for wiring details</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Data sheet for calibration and pressure test</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Hook-up etc. for remote tubing/air line</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">QR for maintaining record</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">WP, work procedure, to check each and every steps as per spec.</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">QCO for issuing in case of little violation</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;"> NCR, for issuing in case of major violation etc.</li>
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18)<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;"> What are the required documents for a remote loop folder?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Following are the required documents for a remote loop folder:</div>
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<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Loop package check list</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">ILD (instrument loop diagrams)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Instrument loop acceptance records(TR/test record)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">P&ID (piping & instrument Diagram)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">ISS/IDS(instrument specification sheet/instrument data sheet)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Alarm List</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Calibration record (TR)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Cable megger report (primary prior to pulling)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Cable megger report (secondary after pulling)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Pressure test record(TR)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">MC check record (remote loop)(green color)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">MC punch list</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Loop check punch list.</li>
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19) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What are the required documents for a local loop folder?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Following are the required documents for a local loop folder:</div>
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<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Loop package check list</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">ILD (if not mechanical loop)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Cable megger report (primary prior to pulling) if not mechanical loop</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Cable megger report (secondary after pulling) if not mechanical loop</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Alarm list ( if not mechanical loop)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">P&ID</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">ISS/ISD (instrument specification sheet/instrument data sheet)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Calibration record (TR)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Pressure test record(TR) if required</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">MC check record (local loop)(green color)</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">MC punch list</li>
<li style="border: 0px none; list-style: disc outside none; margin: 0px 0px 5px 10px; outline: none; padding: 0px;">Visual check punch list/loop check punch list.</li>
</ul>
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20) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is schedule Q?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Schedule Q is an attachment to the contract, which is the provision of quality</div>
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Assurance and control, Inspection and test plan.</div>
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21)<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;"> What is ITPs? What is hold points</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> ITP means inspection and test plan, details of work scope and required types of Inspections</div>
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Hold point (H) is the level of inspection that client inspection must required through RFI and cannot be proceeded until inspection is done by client.</div>
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Witness point (W)   is the level of inspection  that inspection activity can be proceeded without client inspection or if client is not available as per RFI timing.</div>
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22) <strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">What is RFI? When an RFI will be raised?</strong></div>
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<strong style="border: 0px none; list-style: none; margin: 0px; outline: none; padding: 0px;">Ans></strong> Request for inspection (RFI), RFI shall be raised only when the status of the preliminary inspection is satisfactory, and the works (items) are hold or witness point.<br />
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<span style="color: #333333; font-family: Droid Sans, Arial, Verdana, sans-serif; font-size: x-small;"><span style="line-height: 19.5px;">Resource: <a href="http://www.instreng.com/instrumentation-inspection-and-quality-control-questioner/">http://www.instreng.com/instrumentation-inspection-and-quality-control-questioner/</a></span></span></div>
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Instrumentation Inspection and Quality Control Questioner

1)What is QA/QC? Ans> QA/QC means Quality assurance/Quality control the purpose of this (QA/QC) is to establish the sequence of requirement for the quality of material quality of works its inspection…

03 Jul 2014

Over pressure cases for Pressure Relief Valve Sizing

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Separator vessels, storage tanks, heat exchangers, columns and certain piping segments etc. are designed to handle certain operating pressure. However combination of a variety of causes may lead to over pressure in these equipments which may exceed the maximum allowable working pressure (MAWP) value. Pressure Relief valves (PRV) are used to relieve the pressure in these equipments before it can cross the maximum allowable working pressure, thus protecting the equipment from damage. The pressure relief valve set point should be such that relief valve will open before the maximum allowable accumulated pressure (MAWP) is reached in the vessel. For this purpose usually a hydraulic calculation should be done for PRV discharge line to determine the back pressure at the relief valve, which on addition to the pressure drop across pressure relief valve gives the pressure accumulation the equipment.</div>
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The PRV size is based on a minimum relieving flowrate which can prevent the build up of pressure in the protected equipment from exceeding the MAWP limit. For several possible causes of over pressure in the vessel, relieving flowrates are calculated and the maximum of these flowrates is selected for PRV sizing. The over pressure cause corresponding to this flowrate is then known to be the governing case for pressure relief valve sizing. Some common causes of over pressure which are considered for pressure relief valve sizing are described in this article.</div>
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Blocked discharge case</h3>
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This case refers to closure of a valve on the outlet of equipment (vessel, heat exchanger etc). If the fluid still continues to flow into the equipment, absence of an outlet for this fluid results in fluid accumulation and build-up of pressure. This pressure build-up can go as high as the design pressure of upstream pumps or compressors combined with the height of the liquid column upstream. The normal inlet flow in this case in this case should be considered as the minimum relieving flowrate. EnggCyclopedia’s PRV sizing calculator for blocked liquid discharge and for blocked gas discharge can be used to design a pressure relief valve for these scenarios.</div>
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Inadvertent opening of upstream valves</h3>
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Inadvertent opening of valves located at high pressure sources upstream to the protected equipment can result in over pressure in the equipment. This flow can drive the equipment pressure upto design pressure of the upstream high pressure source. The extra flow coming as a result of valve opening should be relieved in this case to protect the equipment.</div>
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Utility failure</h3>
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Failure of utilities such as electricity, instrument air, steam, fuel, cooling water etc. can result in over pressure in related equipments. When analyzing the possibility of over pressure in equipment, possibility of utility failure should be carefully considered. For instance, electricity (for air cooler fans or cooling water circulation pumps) or cooling water failure may result in failure of heat exchangers to meet the duty. Resulting rise in process temperature can cause over pressure in the protected equipment.</div>
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Partial failure</h3>
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In case one source of utility fails but another independent source is still available in parallel to bear complete or part of the extra load caused by partial utility failure, the partially available utility can be considered to evaluate possible over pressure in the protected equipment. Thus, independently available utility alternatives can lower the risk of possible over pressure and should be given consideration at the design stage.</div>
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Heat exchanger tube rupture</h3>
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The tubes in a heat exchanger are prone to failure due to variety of reasons such as corrosion, vibration, thermal shock etc. In such a case flow of fluid from high pressure side of the exchanger to low pressure side causes overpressure on the low pressure side of the exchanger. In this case, the ability of the low pressure side to absorb this overpressure has to be examined and requirement of a relief valve has to be reviewed.</div>
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Fire case</h3>
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Equipment exposed to plant fire has a risk of overpressure in case of fire, resulting from fluid expansion or vaporisation. EnggCyclopedia’s PRV sizing calculator for liquid filled vessel and for gas filled vessel can be used in this case for design of the PRV.</div>
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Transient pressure surge</h3>
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Possibility of ‘water hammer’ in a liquid filled system has to be carefully evaluated, since a  pressure relief valve is usually not able to protect equipment against ‘water hammer’ where pressure can rise to many multiples of operating pressure in matter of milliseconds. PRV takes much longer time to respond to such overpressure creating possibility of equipment damage. Pulsation dampener has to be used in this case as a protection measure. In case of systems filled with gases, ‘steam hammer’ can occur similar to the water hammer.</div>
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Process change / Reaction change</h3>
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In some cases, a significant change in operating process parameters (such as temperature of a cryogenic fluid) can change making the equipment susceptible to damage (temperature of equipment drops below minimum design metal temperature or MDMT). For reacting systems, reactions can shift equilibrium resulting in excess gas or excess heat thus causing over pressure. These possibilities have to be carefully examined for designing the relief valves.<br />
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Over pressure cases for Pressure Relief Valve Sizing

Separator vessels, storage tanks, heat exchangers, columns and certain piping segments etc. are designed to handle certain operating pressure. However combination of a variety of causes may lead to o…

15 Jun 2013

How to Select a Pressure Gauge

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<span style="color: black; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;"><span style="font-family: 'Trebuchet MS';">Mechanical pressure gauges, which require no external power, provide an affordable and reliable source of accurate pressure measurement. The need to select the right pressure gauge requires that the device be accurately specified otherwise numerous problems might surface in the course of using a wrongly selected gauge. The factors discussed here are by no means exhaustive but they are the main things that will assist you to select the right type of pressure gauge. For the right specification and selection process, consult the manufacturer of the particular gauge you intend to use.</span></span><span style="color: black; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;"><span style="font-family: 'Trebuchet MS';"><br /></span></span><span style="color: black; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;"><span style="font-family: 'Trebuchet MS';">Pressure gauges should be selected by considering the factors below to prevent misapplication. Improper application can be detrimental to the gauge, causing failure and possible personal injury or property damage.</span></span><br />
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<span style="color: black; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;"><span style="font-family: 'Trebuchet MS';">To select the right pressure gauge for your application, the following factors should be considered:</span></span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Gauge Accuracy</b><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Pressure gauge accuracy ranges from grade 4A to D according to ASME 40.1. For a mechanical pressure gauge, accuracy is defined either as a percentage of the full-scale range or a percent of the span. As the accuracy increases, so does the price of the gauge. Therefore, the application where the gauge is required should be carefully considered before deciding on the accuracy of the gauge. While requirements differ from one industry to another, the following are general guidelines:</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">• Test Gauges and Standards: 0.25% through 0.10% full scale accuracies.</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">• Critical Processes: 0.5% full scale accuracy.</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">• General Industrial Processes: 1.0% accuracy. Less Critical Commercial Uses: 2.0% accuracy.</span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Gauge Dial</b><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">The dials of pressure gauges come in various sizes. They range from “1.5 to 16” diameters. Generally, the ease with which the gauge could be read, space limitations and accuracy requirements determines the dial size. Larger dial size pressure gauges are required in areas of a plant that are not accessible while smaller sizes are may be required for areas that are easily accessible. The need for higher accuracy in an application may require that a pressure gauge of considerable dial size be used in a given location so as to enable the easy display of small pressure increments.</span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">The Environment</b><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Environmental factors to consider when selecting a pressure gauge include: ambient temperature, air-borne particulate, condensation, humidity, water and chemicals, all of which can affect gauge performance.</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Ambient temperature affects the accuracy and integrity of the gauge. Gauges are available either as temperature compensated or non-temperature compensated. Ambient conditions may require that the gauge be isolated from temperature extremes. When required, the gauge should be isolated from temperature extremes with a flexible line assembly.</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">When ambient conditions are corrosive, contain a large number of particulate or if the gauge will be exposed to a wet or humid environment like humidity, wash-downs or rain, specify a gauge that is weatherproof/hermetically sealed or liquid filled.</span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Process Media/Wetted Parts</b><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Proper selection of the pressure sensor material of the pressure gauge is dependent on the process fluid to which the gauge will be subjected. The material of the pressure gauge sensor should be compatible with the process fluid such that corrosion will not occur. If the correct material is not available and the process fluid is corrosive, the use of a diaphragm seal may be necessary to protect the gauge pressure sensor from the process fluid.</span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Connection Size</b><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Pressure Gauges are available with a variety of connections including NPT, DIN, JIS, BSP & SAE. Process pressure gauges with 41⁄2˝ dial sizes or larger are most often supplied with a 1⁄2˝ NPT connection to best support the gauge. </span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">The main factors to consider when selecting a pressure gauge connection include</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">process pressures, gauge size and weight, space limitations, leak integrity, and of course past experience.</span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Connection Location</b><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">When selecting a pressure gauge, the following mounting options should be considered:</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">• Direct stem mount lower connect,</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">• Remote wall/surface mount lower connect,</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">• Panel surface mount back connect,</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">• Panel hole U-clamp flush mount back connect,</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">• Panel hole front flange flush mount back connect</span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Select the option that best suit your application</span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Pressure Ranges</b><span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;"> </span><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">ASME B40.100 recommends that a gauge with a full scale pressure range of approximately twice the normal operating pressure be selected. The maximum operating pressure should not exceed 75% of the full-scale range. Failure to select a gauge within these criteria may ultimately result in fatigue failure of the pressure sensor inside the gauge e.g Bourdon Tube</span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Pressure Sensor Elements</b><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">The pressure sensor elements in gauges are available in a wide variety of materials, including: brass, phosphor bronze, alloy steel, 316 stainless steel, Monel and Inconel. The selection of the right pressure sensor for the gauge is determined by the process fluid. It is recommended that a sensor element compatible with the process fluid be selected otherwise the use of diaphragm seals is inevitable.</span><br />
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<b style="font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Type of Display</b><br />
<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">Pressure gauges are designed with analog or digital displays. Although the analog pressure gauges are the most popular, the trend in certain applications is moving towards digital displays. The type of application will determine whether an analog or digital display pressure gauge is required. Consult ASME 40.1 and 40.7 for a detailed guide on the use of both analog dial type and digital pressure gauges</span><br />
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<span style="background-color: white; font-family: 'Open Sans', sans-serif; font-size: 13.333333969116211px; line-height: 16.666667938232422px;">The factors discussed above are the main points you need to consider before deciding to specify and select a pressure gauge. Please consult the manufacturer of your gauge for a detailed guide. Before consulting your manufacturer, you might want to go through ASME B 40 for a detailed guideline on pressure gauge specification and selection as this will help you with the selection process with your manufacturer or vendor.</span><br />
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