Es.5.06.0013rasafetyreliefvalves.pdf

  • Uploaded by: Vinod Varadan S
  • 0
  • 0
  • October 2019
  • PDF

This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA


Overview

Download & View Es.5.06.0013rasafetyreliefvalves.pdf as PDF for free.

More details

  • Words: 2,968
  • Pages: 9
Revision A Page 2 CONTENTS 1.0

Introduction

2.0

Custodian

3.0

Purpose

4.0

Application

5.0

Safety relief Valve System

5.1 5.2 5.3

General Relief Valve isolation Relief Valve Installation

6.0

Safety Relief Valve types

6.1 6.2 6.3 6.4 6.5

Selection Common Requirements Conventional Pattern Pilot Operated Pattern Small Relief Valves

7.0

Materials and Testing

8.0

Approval to Deviate

9.0

Revision History

10.0

Glossary

11.0

Bibliography

Revision A Page 3 1.0

Introduction This Design Guide defines the mechanical requirements for safety relief valves for onshore and offshore production and processing facilities. Thermal relieving valves to protect against solar heat input are not covered in this guide. For safety valves in water and steam services, appropriate sections of the American Society of Mechanical Engineers (ASME) code shall apply.

2.0

Custodian The Custodian of this guideline is EE, who is responsible for the accuracy and quality of its contents and for its future revisions, where these are required to reflect industry trends or changes to QGPC business practices.

3.0

Purpose The purpose of this guide is to define the QGPC’s basic mechanical requirements for safety relief valves for onshore and offshore production and processing facilities. Thermal relieving valves to protect against solar heat input are not covered in this guide.

4.0

Application This guideline shall be used by project teams, business units and Contractors or Consultants employed by them. This guide shall form part of the project specification for the new projects (both Greenfield and Brownfield projects).

5.0

Safety Relief Valve System

5.1

General

5.1.1

Pressure relieving devices shall be sized in accordance with API RP 520, Part I. Each device shall be fitted with a stainless steel tag indicating the QGPC tag number.

5.1.2

All safety relief valves shall be shown on the relevant Piping and Instrumentation Diagrams (P&ID's). Each safety relief valve shall be identified with a tag number on the P&ID, and the cold set pressure shall be indicated. Any block valve lock or interlock requirements shall also be shown.

5.1.3

A Process Data Sheet shall be prepared for each safety relief valve, giving all the process data required to properly size and select the valve. As well as basic information such as pressures, temperatures, flowrates, viscosity and the like, the data sheet shall also indicate other relevant factors where applicable, e.g. possible solids formation, dangerous fluids, fluctuating back pressure, mixed-phase flow etc.

Revision A Page 4 5.2

Safety Relief Valve Isolation

5.2.1

The preferred arrangement has the safety relief valve directly piped from the protected equipment to the flare system, with no intervening block valves. Where this is not possible due to operational priorities, any block valves used shall be of full bore type and their status, i.e. open or closed, shall be clearly evident from visual inspection.

5.2.2

Any arrangement utilising isolation valves requires the highest standards of operation, procedural control and maintenance, supplemented by mechanical lock systems.

5.2.3

Utilisation of a means of isolation both upstream and downstream of a safety relief valve is the least preferred option and only acceptable where a shutdown of both the protected system and the flare/vent system is unacceptable. This arrangement requires the installation of spare safety relief valve (s) and may be considered if a frequent safety relief valve inspection or maintenance requirement exists which cannot be accommodated during normal shutdowns. Spare safety relief valves should be isolated upstream when not in service to avoid potentially damaging valve chatter.

5.2.4

Where provision is made for a spare safety relief valve, the downstream block valve shall be locked open if the set pressure of the safety relief exceeds the pressure/temperature limits of the downstream block valve or any of the pipework between the block valve and the safety relief valve.

5.2.5

Where isolation is required on the upstream side of relief valves, this shall be carried out by means of single block and bleed or double-block-and-bleed valving, depending on pressure rating and operating philosophy. Pressure drop between vessel and relief valve shall not exceed 3% of set pressure; this may prevent the use of double block and bleed valves in some instances. Single block isolation downstream of the relief valve is normally adequate for low pressure flare systems.

5.2.6

The locking system shall ensure that isolation valves allow 100% relieving capacity at all times, in addition to providing isolation for each individual safety relief valve. The locking system shall be quick to operate and of such a design that a master key can be provided for use in emergency situations.

5.3

Safety Relief Valve Installation

5.3.1

All safety relief valves shall be installed in the upright position with the stem vertical. Piping shall be designed free draining away from the safety relief valve at both inlet and outlet.

5.3.2

Sufficient access shall be provided for maintenance, inspection, removal or replacement of safety relief valves. For safety relief valves of a size or weight that are not easily handled, consideration shall be given to the provision of lifting points or runway beams.

5.3.3

Piping systems shall be designed to withstand safety relief valve reactive forces at relief valve "pop" condition as well as established flow condition. Due consideration shall also be given to thermal expansion and contraction.

Revision A Page 5 6.0

Safety Relief Valve Types

6.1

Selection

6.1.1

For purposes of discussion, safety relief valves are divided into three basic types: conventional pattern, pilot operated and small valves. Conventional pattern valves are used for most services, because of their relative simplicity and reliability. Inlets and outlets are always flanged, with inlet sizes ranging from 1" to 8" and pressure ratings from Class 150 to 2500. Balancing bellows and pistons may be specified as additions to the basic valve as described in section 6.3.

6.1.2

Pilot operated valves are available in similar size and pressure ranges to conventional pattern, and also have flanged inlets and outlets. For the same relieving capacity they are generally smaller and lighter. They also provide a tighter closure where operating pressure is greater than 90% of set pressure, and in gas service where conventional valves might experience seat leakage. Because of possible problems with blockage of the small-bore pilot valve or tubing, their use should only be considered in clean dry gas service. Refer to section 6.4 for further details of valve configuration.

6.1.3

Small safety relief valves are here defined as those having inlet sizes of 3/4" or below. They are used for very low flow applications, such as thermal relief of liquid inventories or protection of small air receivers or positive displacement pumps. Inlet and outlet connections may be threaded for non-hazardous services, but shall be flanged for all process or hazardous fluids. Selection between the various types of small valve shall be made on an individual basis, using section 6.5 for additional guidelines.

6.2

Common Requirements

6.2.1

Except where otherwise specified in this document or in the requisition, conventional and pilot operated valves shall be supplied in accordance with API 526.

6.2.2

Inlet connections shall be of sufficient strength to withstand the reaction force of valve discharge, as well as being suitable for the set pressure and design temperature. The minimum flange rating in process service shall be Class 300. Outlet connections shall be suitable for the design pressure/temperature conditions of the downstream pipework; outlet flanges shall be Class 150 minimum rating.

6.2.3

Inlet and outlet flanges shall be raised face and in accordance with ASME B16.5. Threaded connections if permitted shall be to ASME B1.20.1, including bonnet vent connections where applicable.

6.2.4

Valves shall be of the enclosed spring type.

6.2.5

The design of the safety relief valve shall be such that no liquid can collect on the discharge side of the device.

6.2.6

Safety relief valve seats shall normally be metal to metal. Where a tighter shut-off is required, the use of elastomeric seals suitable for the service conditions may be considered. All soft seats shall be renewable. Metal to metal seats shall be of ample proportions, so as to permit several lapping or re-machining operations.

6.2.7

For high temperature applications in excess of 200°C, metal to metal seats shall be used. For high pressure drop applications in excess of 7.0 MPa, stellited trim shall be used.

Revision A Page 6 6.2.8

The Vendor shall check all safety relief valves sizing in accordance with the information on the Data Sheet and the Purchase Order. Vendor shall submit calculation sheets for each safety relief valve to the Purchaser for approval prior to manufacture. The Vendor shall inform the Purchaser of any inadequacies in the information supplied to the Vendor for valve sizing, materials of construction or in safety relief valve selection for the specified service. The Vendor shall also submit noise calculations for each safety relief valve in dBA at full lift. The sound pressure level at 1 metre distance from the safety relief valve shall not exceed 85 dBA.

6.2.9

The spring in a safety relief valve in service for set pressures up to and including 1.7 MPag shall not be reset for a set pressure more than 10% above or 10% below that for which the valve is marked. For higher set pressures, these limits shall be 5%.

6.2.10

The set pressure tolerances, plus or minus, of safety relief valves shall not exceed 15 kPag for pressures up to and including 500 kPag and 3% for pressures above 500 kPag.

6.2.11

Safety relief valves shall not be fitted with manual seat lifting devices, or with test gags, unless specifically requested in the requisition.

6.3

Conventional Pattern

6.3.1

Conventional pattern valves shall be in accordance with "direct spring-loaded" valves as specified in API 526, except where modified by the requirements herein.

6.3.2

Valves shall be full nozzle type, so that the nozzle and seat are the only parts in contact with the process fluid when the valve is closed.

6.3.3

A balanced bellows may be specified as an addition to a conventional relief valve. This device isolates the spring, bonnet space and internals from the inlet and outlet fluid. Where fluctuating imposed back pressure is possible, or where built up back pressure may exceed 10% of set pressure, a balancing bellows shall be used. It may also be specified to prevent corrosive, dirty or hazardous fluids contacting the valve topworks, or leaking to atmosphere.

6.3.4

Where a balanced bellows is fitted, the bonnet shall be vented, either locally or to safe location depending on the nature of the fluid. Means shall be provided to monitor the integrity of the bellows. In cases where bellows failure would cause a dangerous condition due to backpressure as described above, a balancing piston shall also be specified. This functions as a back-up device to the bellows and ensures proper valve operation in the event of bellows failure.

6.4

Pilot Operated Pattern

6.4.1

These valves shall be generally in accordance with API 526, except where modified by the requirements herein. Non-standard valves may be considered on an individual basis for special applications. Valves shall not be supplied with back flow preventers, or with field set pressure checking devices, unless specified in the requisition.

6.4.2

This pattern shall not be used on services where the small bore pilot valve, or its pickup or discharge piping, might be subject to blockage. Such services include dirty, wax-forming or freezing fluids. In the event of failure of the pilot valve system, the main valve shall still open at an increased overpressure.

Revision A Page 7 6.4.3

The preferred configuration for pilot piping shall be pickup from a connection on the main valve inlet, and discharge to a connection on the main valve outlet. Where a remote pressure pickup is required, this shall be specified in the requisition.

6.4.5

The Vendor shall review the back pressure conditions on the data sheet and advise where the pilot valve discharge piping should route to atmosphere for satisfactory main valve operation. If atmospheric discharge is essential, the Vendor shall advise the fluid volume which would be vented under relieving conditions.

6.4.6

Pilot operated safety relief valves shall be constructed to provide a facility for tamper proof sealing, preferably by wiring of screw cap and body on the pilot valve and lead sealing, to ensure setting integrity.

6.4.7

Pilot valves shall be of the non-flowing type, and shall be spring loaded and soft seated where the temperature permits. All materials shall be compatible with the process fluid.

6.4.8

Pilot tube and fittings shall be stainless steel and shall be 10 mm O.D minimum. Fittings shall be compression type. Flared tube fittings shall not be used.

6.5

Small Relief Valves

6.5.1

These valves are not covered by any International standard for constructional details. Full vendor drawings and parts lists shall be required for each individual valve. Capacity certification shall be to ASME requirements, or to other equivalent International standards as approved by the Purchaser.

6.5.2

Where flanged connections are selected, these shall be of lap-joint stub end type construction, with the stub end of material grade equivalent to the base nozzle i.e. stainless steel type 316 or better.

6.5.3

Fixed blowdown type may be used where the operating pressure is less than 75% of set pressure. For higher operating pressures, adjustable blowdown shall be specified.

6.5.4

In normal operating mode i.e. valve closed, the only valve parts contacting the fluid shall be of stainless steel type 316 or better.

6.5.6

The maximum orifice size for this type of valve shall be 71 sq.mm.

7.0

Materials and Testing

7.1

Materials of construction for major components shall be specified by the purchaser on the data sheet. The vendor shall provide full material specifications for all components in his quotation. After order, the vendor drawings submitted for formal acceptance shall also show this information.

7.2

Construction materials for sour gas service shall conform to NACE MR0175 and QGPC Standard 153 (Materials for Sour Service). For pressure relieving valves in unusually corrosive process conditions, body, bonnet, and trim materials shall be approved by QGPC.

7.3

Pressure relieving valves with soft seats or secondary O-rings may be used for special services, such as hydrogen service at moderate temperatures, subject to QGPC approval.

Revision A Page 8 7.4

An ASME code stamp is not required, but capacities of valves shall be certified by the manufacturer using the methods outlined in ASME code section VIII and API 520.

7.5

Pressure relieving valve bodies shall be pressure tested with air or water in the vendor's shop before set pressure and leakage tests are conducted. The valve shall be tested after assembly with a gag in place. The gag shall be removed prior to set pressure and leakage tests. The valve body shall be tested as follows: •

Inlet side shall be tested at 1.5 times the design pressure of the primary pressure parts.



Outlet side shall be tested at 1.5 times the maximum allowable backpressure. Minimum test pressure shall be 207 kPa.

7.6

Valves of all suitable configurations shall be tested for seat tightness in full accordance with API 527, and the results of such tests shall form part of the certification requirements. For gas, vapor and air service, the test medium shall be air. For liquid service, the test medium shall be water. Where the configuration of the valve precludes tests to API 527, the vendor shall formally propose alternative testing procedures for acceptance by QGPC.

8.0

Approval to Deviate Strict compliance with this guideline is required. Any deviation must obtain prior written approval from its custodian.

9.0

Revision History A log is kept of the revision history of this document, and incorporated in the electronic “readme” file (ES.5.06.0013R).

10.0

Glossary Within the context of this Design Guide the following words shall have the meanings stated:

"must/shall"

- Indicates a mandatory requirement.

"should"

- Indicates a preferred course of action.

"may"

- Indicates one acceptable course of action.

"approval"

- Indicates agreement/sanction and shall be in writing only.

Purchaser

- The organisation responsible for performing the purchasing function, eg QGPC or a QGPC appointed Contractor, Consultant or Agent.

QGPC

- Qatar General Petroleum Corporation

Vendor

- The supplier of material or equipment – not necessarily the Manufacturer

Revision A Page 9

11.0

Manufacturer

- The company responsible for the manufacture - not necessarily the Vendor.

Contractor

- The QGPC appointed main Contractor for a defined piece of work.

Sub-contractor

- A company awarded a contract by a Contractor to do part of the work awarded to the Contractor by QGPC. The work of the Subcontractor is carried out under the direction and control of the Contractor. Under its model contracts QGPC has the right to review all proposed Sub-contractors, and sub-contracts.

Consultant

- A company awarded a contract by QGPC for the company to advise or give guidance on specific subjects. The Scope of Work may include instructions to act as an Agent for QGPC

Bibliography The following standards, codes and specifications shall, to the extent specified herein, form a part of this Design Guide. Except where a specific edition or revision is identified by date or revision/edition number, the edition in effect at the time of the contract shall govern.

11.1

11.2

International Standards API RP 14C

- Recommended Practice for Analysis, Design, Installation and Testing of Basic Surface Safety Systems on Offshore Production

API RP 520 I

- Sizing, Selection and Installation of Pressure-Relieving Devices in Refineries, Part I - Sizing and Selection

API STD 525

- Testing Procedure for Pressure-Relieving Devices Discharging Against Variable Back Pressure

API STD 526

- Flanged Steel Safety-Relief Valves

API STD 527

- Commercial Seat Tightness of Safety Relief Valves with Metal-toMetal Seats

ASME SEC VIII

- Boiler and Pressure Vessel Code Rules for Construction of Pressure Vessels

NACE MR-01-75

- Standard Material Requirements for Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment

QGPC Documents QGPC Std. 153

- Material for Sour Service

More Documents from "Vinod Varadan S"