API 598: Valve Inspection and Testing

Reviewed by the Crestflo Engineering Team

API 598, "Valve Inspection and Testing," is the American Petroleum Institute standard that sets the inspection, examination, and pressure-test acceptance requirements a valve must meet before it ships. It defines four core tests: shell, backseat, high-pressure closure, and low-pressure closure. The standard spells out the pressures they run at and the allowable leakage by seat type. Crestflo instrumentation valves get 100% seat- and shell-leak testing in house, and they can be tested to API 598 acceptance criteria on request. EN 10204 material traceability comes standard, and delivery runs 6–8 weeks.

Scope note: API 598 is the API standard for valve inspection and testing. It's not the API gravity scale that grades crude oil, and it isn't a part number either. On this site, "valve" refers to an instrumentation valve (ball, needle, check, manifold, monoflange), not something you'd find in plumbing or under the hood of a car. Think of API 598 as an acceptance and test standard. Valve design is a separate matter, covered by specs such as ASME B16.34, API 600/602/608/609.

Request API 598 test documentation & RFQ → · sales@crestflousa.com · +1 346 594 9005

Also known as: API 598 designations & related terms

Specifications and datasheets label this standard in several different ways. Every designation below points to the same valve inspection-and-testing standard.

API 598 standard at a glance: attributes

Exact hold times and metal-seat leakage-rate tables, broken down by size, are copyrighted material fixed in the current edition of the standard. This page won't reproduce them. Instead it covers scope, test types, pressure bases and how acceptance is determined. Values follow the applicable standard and can be adjusted to your requirement.

What is API 598?

API 598, "Valve Inspection and Testing," is an American Petroleum Institute standard. It spells out the inspection, examination, and pressure-test acceptance requirements a valve must meet before it ships. The American Petroleum Institute (API) publishes it, and it covers gate, globe, check, ball, plug and butterfly valves.

API 598 is a test-and-acceptance standard, not a design standard. It does not tell a manufacturer how to size a body wall or rate a valve, that belongs to design specifications like ASME B16.34, API 600, API 602 and API 608. Instead, API 598 tells the inspector which tests to run, at what pressure, for how long, and how much leakage is acceptable, so a buyer or third party can accept the valve on an objective basis.

API valve specifications show up constantly in the standard's language: a valve built to API 602 or API 608, say, gets pressure-tested against API 598 criteria. That's the reason "tested to API 598" turns up on so many valve datasheets. It's the shared acceptance-test language running through the whole family of API valve specifications.

Who publishes API 598, and what is the latest edition?

The American Petroleum Institute (API) writes and maintains API 598. API revises its standards on a periodic cycle, and the 10th edition (2016) is the version most widely cited in current specifications. Cite the edition named in your project specification, and confirm it against the current API catalog, since contract references vary by edition.

Where can I get the API 598 PDF?

API 598's full text is a copyrighted, licensed document, sold by API and authorized resellers such as ANSI and Accuris. What follows here is a summary: the standard's scope, its test types, pressure bases, and acceptance logic, laid out for engineering reference only. Nothing here reproduces or distributes the document itself.

Compliance work calls for the current official edition. Skip the unofficial "free download" copies floating around online; they can easily be superseded versions.

API 598 scope: inspection, examination & pressure testing

API 598 governs four activities a valve passes through before acceptance:

• Inspection, verification that the valve conforms to the purchase order and its design/material requirements.
• Examination, visual examination of the valve and its markings.
• Supplementary examination, non-destructive testing (radiographic, ultrasonic, liquid-penetrant, or magnetic-particle, RT, UT, PT, MT), applied only when purchaser and manufacturer agree to it.
• Pressure testing, the shell, backseat and closure tests that make up the core of the standard.

Because it is an acceptance standard, API 598 defines what must pass rather than how the valve is engineered. The pressure–temperature rating the tests are referenced against comes from the design standard, typically ASME B16.34, while fire resistance, fugitive-emission limits and pipeline-service requirements are covered by separate standards (see the comparison below).

API 598 valve types covered: gate, globe, check, ball, plug & butterfly

API 598 applies to six valve families: gate, globe, check, ball, plug and butterfly valves. The test logic isn't uniform across these types; it shifts depending on what the valve actually does. A backseat test, for instance, only makes sense on rising-stem valves. A check valve, meanwhile, gets checked for backflow tightness rather than a two-way seat.

Crestflo also makes small-bore instrumentation counterparts of several of these families: ball valves, check valves / NRV, and plug valves. Add to that needle valves and manifolds, all seat- and shell-leak tested under the same acceptance logic. The conformance section below explains how API 598 criteria apply to instrumentation valves.

The four API 598 tests explained: shell, backseat & closure

API 598 is built around four pressure tests. Each one has its own pressure basis and its own acceptance criterion.

Shell test. This one proves the pressure boundary, body and bonnet, holds without leaking. It runs at 1.5 times the 38 °C (100 °F) maximum pressure rating, with the valve partly open and a liquid medium (a hydrostatic, or hydro, test). Zero visible leakage through the body walls is required.

Backseat test. This applies only to rising-stem valves. With the stem backseated, the valve gets pressurized to 1.1 times the 38 °C (100 °F) rating to prove the backseat seals. Here too, zero visible leakage is required.

High-pressure closure (seat) test. This checks seat tightness with the valve closed, using a liquid at 1.1 times the 38 °C (100 °F) rating. Whether it passes depends on the seat type, see the leakage table.

Low-pressure closure (seat) test. Seat tightness gets checked again here, this time with air or inert gas at roughly 60–100 psi (about 4–7 bar). Gas will find leaks a liquid can mask. As before, acceptance depends on the seat type.

An optional high-pressure pneumatic shell test, using air or an inert gas, can be added by agreement when a project calls for it. The requirement is zero visible leakage.

API 598 test pressures & test fluids

Table A, API 598 test pressures. Every base ties back to the valve's 38 °C (100 °F) maximum pressure rating, drawn from the design standard (e.g. ASME B16.34).

Test fluids and the chloride caution. API 598 allows water, air, inert gas, or kerosene as test media. When water goes into austenitic stainless steels, the chloride content gets limited, and the valve gets rinsed and dried, to avoid chloride stress-corrosion cracking and pitting. That's the same reason 316/316L service calls for chloride control. Values follow the applicable standard and can be customized to requirement.

API 598 test durations & allowable leakage rates

API 598 lays out minimum hold times in Table B, and they climb as valve size (NPS) grows. Larger valves simply sit under test longer. Shell, backseat, and closure tests each carry their own separate minimums, too. The exact per-size figures come from whatever edition of the standard is current, so they aren't reproduced here.

Table C, allowable leakage by seat type. Whether a valve passes the closure tests depends on the seat material: resilient (soft) or metal. The split specifiers refer to what API 598 calls the leakage class. Resilient-seated valves must show zero visible leakage. Metal-seated valves get a size-dependent rate instead. Leakage gets measured in drops per minute for the liquid test, or bubbles per minute for the gas test.

Metal-seat maxima per size come straight from whichever edition of API 598 is currently in force. A "drop per minute" or "bubble per minute" is the standard unit used to record leakage during the timed hold. Values follow the applicable standard, though they can be adjusted to fit a particular requirement.

API 598 vs API 6D, API 607, ISO 5208 & ASME B16.34

API 598 is one member of a family of valve standards, and specifiers routinely ask how it differs from its neighbors. API 598 is purely an inspection-and-testing acceptance standard; the others cover different valve populations or different failure modes altogether.

API 6D and API 598 differ in scope. API 6D is a full specification for pipeline valves that includes its own testing, whereas API 598 is a stand-alone acceptance-test standard used across general industrial valve types.

For ball valves, the comparison shifts to API 598 vs API 607 for ball valves. API 598 covers routine pressure and seat leak checks. API 607, by contrast, is a fire test that qualifies a valve to seal after fire exposure. Neither one replaces the other; they work together.

How Crestflo tests its valves to API 598 acceptance criteria

Crestflo instrumentation valves get 100% seat- and shell-leak testing in house, and can be tested to API 598 acceptance criteria on request. Every valve comes with a full test regime and complete material traceability behind it. Hydraulic proof, hydraulic burst, hydraulic impulse and pneumatic testing all happen in house, along with PMI (positive material identification) and in-house NDT. Destructive testing goes out to ISO/IEC 17025-accredited laboratories, and third-party inspection is available on request.

An honest applicability note. API 598 is written for industrial and pipeline valves. Small-bore instrumentation valves are usually tested to ISO 5208, MSS SP-99, or a manufacturer standard, with API 598 acceptance criteria applied where a project specifies it. Crestflo instrumentation valves get 100% seat- and shell-leak testing no matter what. When your specification calls API 598, the Engineering Team confirms the applicable test and issues the documentation. Certificates and traceability records are held in quality / traceability; the full program is described under testing & inspection.

Ask for API 598 test documentation on your valves →

Request API 598-tested instrumentation valves

Send your requirement, valve type, material/grade, size and end connections, pressure rating, quantity, plus any test standard (API 598, ISO 5208) or NACE sour-service target, and the Crestflo Engineering Team will confirm the valve and test documentation for your line.

RFQ, tell us what you need:

• Name
• Company name
• Email
• Phone
• Requirement description (valve type, material, size, rating, quantity, test/service conditions)

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Secondary paths: browse instrumentation valves · request your part-number cross-reference · become a distributor · contact Crestflo.

US contact: sales@crestflousa.com · +1 346 594 9005 · Houston, TX.

Ready stock covers standard items; specials are made to order, with delivery running 6–8 weeks. Origin is Indian, though US or European melt can be supplied on request, backed by full material traceability.

Why Crestflo for API 598-tested instrumentation valves

API 598's tests, pressures, and leakage criteria are laid out here as HTML-native data, not buried in a PDF somewhere. Crestflo instrumentation valves are 100% seat- and shell-leak tested in house, and we'll provide API 598 acceptance criteria on request.

Crestflo is a manufacturer, not a reseller, we build the valves and we run the tests ourselves. Hydraulic proof, burst and impulse, pneumatic, PMI, and NDT all happen in house. Destructive testing goes out to ISO/IEC 17025-accredited labs. Third-party inspection is available on request.

Every part carries traceability. That means an EN 10204 3.1 MTC (3.2 on request) plus a heat/lot number on every part. It's the paper trail connecting "we tested it" to "here's the proof."

• Lead time that moves projects. Ready stock for standard items, made-to-order for specials, 6–8 week delivery.
• Honest origin. Indian origin; US / European melt available on request, with full material traceability.
• Small MOQ and private label, both imperial and metric, customizable to requirement.
• Certified quality system: ISO 9001 / 14001 / 45001 & PED certified.

Crestflo is the instrumentation division of a four-decade-old export house, one recognized by the Government of India, with a long record of delivering across the Middle East. There's real manufacturing pedigree behind this focused, US-serving instrumentation brand. We Engineer Confidence.

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Explore related standards, valves & documentation

Standards: Standards hub · API 6D · API 607 · API 6FA · API 602 · ASME B16.34 · ISO 15848 · NACE MR0175 · EN 10204 MTC

Valves: Instrumentation valves · Ball valve · Needle valve · Check valve / NRV · Double block & bleed · Monoflange valve · 3-valve manifold

Materials & quality: 316/316L · Traceability · Testing & inspection