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  • Writer's pictureSteady Marine

Sea Valve Leakage Allowances

Sea valves in dry dock periods are one of the biggest parts of the scope. ‘ABS Rules for Survey After Construction Part 7 Chapter 4 Section 1’ states:

“(2005) When a vessel is in drydock or on a slipway, it is to be placed on blocks of sufficient height and with the necessary staging to permit the examination of the following items which are to be cleaned, as necessary, and examined together with appendages, as applicable, and placed in satisfactory condition:

xx) (2005) Sea connections and overboard discharge valves and cocks, including their attachments to the hull or sea chests, are to be externally examined. Valves and cocks need not be opened up more than once in a Special Periodical Survey period unless considered necessary by the Surveyor.”

Once valves are opened up, usually the attending class surveyor would like to see the seat & disc surfaces cleaned up. In very specific occurrences the tightness of valve discs could be subject to a tightness test. I was wondering what would be the leakage rate in such a case If any is allowed at all.

Let’s start with IACS- As per ‘IACS Req. 1974/Rev.7 2019 - G3.6 Tests of piping components and pumps prior to installation on board - G3.6.1 Valves - G3.6.1.1 Prototype Testing’:

“Each type of valve intended to be used at a working temperature below -55ºC shall be subject to the type tests defined in to of the IGC Code (Resolution MSC.370(93)).”

So IACS drops the ball to ‘Maritime Safety Committee’ when it comes to leakage allowances on sea valves. According to ‘MSC 93/22/Add.1 Annex 6, page 90 5.13 Testing requirements -5.13.1 Type testing of piping components - Valves’:

“Each type of valve intended to be used at a working temperature below -55oC shall be subject to the following type tests: .1 each size and type of valve shall be subjected to seat tightness testing over the full range of operating pressures for bi-directional flow and temperatures, at intervals, up to the rated design pressure of the valve. Allowable leakage rates shall be to the requirements of the Administration or recognized organization acting on its behalf.”

The definition of "Administration" per MSC.370(93) is: “1.2.3 Administration means the Government of the State whose flag the ship is entitled to fly. For Administration (port), see port Administration” Meaning that It is flag state and/or class surveyor in most cases.

After all these regulatory references made it looks like it comes back to surveyor’s interpretation. As a surveyor’s hand’s book let’s have a look at ‘ABS Rules for Building and Classing, 4-6-2, 7.3.2 Hydrostatic Tests of Shell Valves (1 July 2021)’ It says:

“The valve assembly is to be subjected to a hydrostatic seat leakage test in accordance with a national or international standard accepted by the Surveyor. The test is to be performed with closed valve with the other end open to atmosphere. The pressure is to be applied independently on each side. Test pressure is not to be less than 5 bar (5.1 kgf/cm2, 72.5 psi). holding time is 5 minutes for all sizes.”

The key term here must be ‘national or international standard’. ‘US Code of Federal Regulations, 46 CFR 56.01-2 Incorporation by reference’ recognizes below standards with below-accepted leakage rates:



3. MSS SP-61-2009 Test Standards

This is the test standard that covers other below-listed MSS valve standards. The Manufacturer’s Standardization Society also has a section on valve leakage in Section 5 of their ‘Pressure Testing of Steel Valves - MSS SP-61-2009’. It covers on-off valves. Not control valves. The following leakage rates are deemed acceptable by this testing standard: For comparison purposes, the following are examples of leakage rates as noted in the MSS Specifications below:

• 10ml liquid = 2 teaspoons = 1/3 oz. = .001 litres

• 40ml liquid = 3 teaspoons = 1 1/2 oz. = .004 litres

METAL SEATED - GATE, GLOBE, BALL OR BUTTERFLY VALVES: 10 cc/hr per inch of nominal pipe diameter per hour. This equates to 2.66 drops/min/inch. For air test 1180 bubbles/min/inch is allowed. (e.g. A 6” globe valve is allowed to leak 60 cc/hr in a test). Metal Seated knife gate valves to MSS SP-81 are not included, refer to MSS-SP151 (see below) which allows 40ml/min/inch at 40 psi (275 kPa). All shut-off or isolation valves specified to MSS-SP-61 must pass the above standards. The seat closure test must be performed at a fluid (liquid or gas) pressure no less than 1.1 times the 1000°F (380°C) rating rounded to the next 5 psi (0.5 bar).

The MSS SP-61 leakage rate is specified for resilient and metal seated check valves, however some manufacturers commonly specify a guaranteed maximum leakage for resilient seated check valves. For metal and resilient seated check valves the leakage rates referred to in MSS SP-81 for knife gate valves is often specified.

As conclusion, although some standards allow minor levels of leakage on valve discs it is highly recommended that projects teams should put their best effort to overhaul a sea valve to non-leakage tightness for a piece of mind and hassle-free dry docking operation.

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