Safety valves Overhaul | Calibration

Periodic Verification and Reference Legislation

The periodic check of the safety valves is one of the activities foreseen by the legislation in force for the purposes of the correct maintenance of the systems as prescribed by the D.M. n. 329 of 1 December 2004.

Verification of operation during periodic checks “can be carried out with bench tests, with simulations, or, where not detrimental to the operating conditions, by determining the intervention on site.”

In particular, “the verification may consist in ascertaining that calibration has taken place within the time limits established by the manufacturer and in any case within the limits relating to the periodicity of the requalification checks.” (Article 13, paragraph b).

“The checks relating to safety and pressure accessories follow the same frequency as the pressure equipment to which they are intended or to which they are connected.” (Article 10, paragraph 4)

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Overhaul and Calibration in the Workshop

During the periodic checks it is good practice to overhaul the valve.
The maintenance of the safety valves in our workshops involves the following phases:

internal and external sandblasting of the valve body;
decomposition of the valve and first evaluations;
thorough cleaning and control of each component;
check sealing surfaces of shutter / seat;
execution of restoration works and replacement of any gaskets;
turning and / or lapping of the shutter / seat sealing surfaces;
greasing rod / guide / spring adjustment screw couplings;

reassembly of the valve and seal test of the obturator / nozzle;
bench valve calibration (according to API STD 527);
painting;
release of audit reports;
coordination with ASL, INAIL or other supervisory body;
calibration certificate issue.

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Review and Calibration in the Plant

The maintenance of safety valves with welded inlet connection is usually carried out directly on site and includes the following steps:

decomposition of the valve and first evaluations;
phorough cleaning and control of each component;
check sealing surfaces of shutter / seat;
execution of restoration works and replacement of any gaskets;
turning and / or lapping of the shutter / seat sealing surfaces;
greasing rod / guide / spring adjustment screw couplings;

reassembly of the valve and test with blue shutter / nozzle;
release of audit reports;
calibration with the system running with an ASL, INAIL or other control body;
calibration certificate issue.

Calibration in Place by means of Trevitest

Calibration is carried out using the TREVITEST, INAIL approved equipment, according to the standards contained in paragraph E1D2.11.2. of Collection E, without disconnecting the valve and in continuity of operation.

The TREVITEST is an equipment consisting of a hydraulic device capable of applying a force to the stem of the safety valve and a measuring system that detects and records the force applied, highlighting the value necessary to cause the shutter to open.