GN 021 - Use & In-service Inspection of Gas Accumulators
- Details
- Category: Use & In-Service Inspection
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APEK |
IN-SERVICE INSPECTION & CARE OF GAS ACCUMULATORS |
APEK GN 021 Draft: 5 Issued: 24/03/2014 |
Developed for: ACA, AICIP, AIES, AINDT, CAAA, Eng Aust, Met. Aust, NATA, Stds Aust, WTIA, & PE Industry & Regulators
1 Scope
This note:
a) gives guidance on the above subject and in particular high pressure types charged with inert nitrogen.
b) deals primarily with steel accumulators but gives some guidance on other materials.
c) is intended to clarify a number of issues of concern to industry, to help comply with new Work Health and Safety (WHS) laws which are being consolidated across Australia, and to complement AS/NZS 3788 (Ref 1) with more details.
d) excludes:
(i) large dead weight hydraulic accumulators, steam accumulators, hydraulic surge vessels, domestic type air-water vessels, gas cylinders covered by Dangerous Goods laws, and
(ii) similar looking pressurised equipment classed as "machines" not pressure vessels ie snubbers, hydraulic rams shock absorbers, pressure struts and similar machines which are not required to be registered but must be safe.
2 Background
These vessels are hazardous and with hazard levels to AS4343 ranging from E to B and in Australia. They are specifically covered in AS/NZS 3788, but often unrecognized or forgotten. There is confusion on registration and many are not registered and contravene WHS Regulations. Hence guidance is needed for all - especially users and inspectors - with the new WHS Regulations.
3 Definition
These are pressure vessels which absorb or store pressure energy to reduce pressure shock in liquid systems or xxxx closures. They include vessels known as dampeners, air-water vessels, surge vessels and diaphragm type expansion vessels in hot water generating systems. Free piston hence not a machine
4 Types
.1 Four types are: bladder, diaphragm, piston, and miscellaneous/special, all using gas (mainly nitrogen) in a bladder or in the body. See Fig 1.
.2 Pressures usually range from 3 MPa (30 bar) to 50MPa (500bar).
.3 Volumes range from a few to 100 litres. The larger ones are usually piston or special types.
.4 Bodies are usually cylindrical with forged or threaded flat ends with openings, or spherical with welded halves.
.5 Materials are usually heat-treated Carbon, C-Mn, and low alloy steel, and more recently aluminium, titanium or fibre reinforced plastic (FRP).
.6 All are produced to Standards governing design and manufacture and bodies are similar to forged or FRP gas cylinders.
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a) Typical bladder type |
b) Typical piston type (with free piston) |
Fig 1 Main Types of Accumulator
5 Use
.1 Mainly in hydraulic systems in machines and various plant eg high pressure injection moulding machines, EWPs, fire doors, etc, with non-flammable, non-toxic hydraulic fluid or lubricating oil.
.2 In AU the estimated number in use is about one million.
.3 Selection of type, size and pressure depends on service requirements and conditions.
6 Service Conditions
These vary with different applications and influence the required type, care, inspection, safe life and performance of accumulators.
Conditions include: Pressure, service temperature, number of pulsation cycles, desired life, severity of shock, whether on transportable plant and location, eg near sea or in corrosion environment, or requiring protection against external corrosion, abrasion, impact and security.
7 Hazards
Main hazard is severe injury or damage from unwanted sudden release of high pressure stored energy - in some cases equivalent to 1 kilogram of TNT, eg due to:
a) violent rupture of the accumulator shell or body and other pressure parts can results from undetected severe fatigue cracking, overpressure, fire, corrosion or abrasion, or impact by adjacent equipment or projectiles.
b) closures and connections suddenly failing or releasing due to poor connection. See 9.3 below.
8 Hazard Level
AS 4343 Ref 2 gives these as: eg
HL B: P x V 1000 MPa.L. eg 30 MPa pressure (P) and 35 L volume (V)
HL C: 100. 20. 5 L
HL D: 30. 20. 1.5 L
HL E: P x V is below 30 MPa (HL A is above the range for accumulators)
9 Experience
.1 Excellent with very few serious failures in the world.
.2 While the hazard can be high, risk is generally low (because of excellent manufacture, proper care and periodic in-service inspection). Risk can be very high in some applications without such controls.
.3 One person was killed in NSW in 1980s due to ill-fitting closure released violently on repressurising. The most dangerous times are on charging and recharging which require competent personnel.
.4 Failure causes can be: Material defects, bladder or piston seal leakage, "frost heave" in very cold service, dents and gouging, corrosion, fatigue, overpressure, and joint leakage.
10 Design And Manufacture
All are designed and manufactured to recognise Standards. Some or most built to seamless gas cylinder standards. Later to BS 7??? (Ref 4) or ISO14??? (Ref 5) for particular pressure, temperature, often with no corrosion allowance. For the requirement P, T are corrosion allowance. Almost all made overseas in 3 or 4 plants, for various suppliers. Some are manufactured from the same pipe as for drill casings with ends formed by forging or with internal end threads for inserted ends.
11 Supply
By AU importers and suppliers or already installed on package equipment or modules supplied complete from overseas.
Compliance with WHS Regulations is the responsibility of supplier who should ensure:
a) the quality and safety is from competent manufacturers.
b) provision of MDR and instructions and preferably with design registration.
c) inspection shows accumulators are not damaged in transport, are suitably packaged for protection, fully identified with complete markings and notices.
d) have essential spares and instructions on instal, rego, operation, maintenance, life or use by, hazards and safety.
12 Installation
Accumulators should normally be installed:
a) in a vertical position with suitable safety devices.
b) with suitable support (base and straps) and protection from rain and impact.
c) with clearance for installing and connecting to piping, for charging and recharging, and leak testing and installer inspection; with suitable personnel safety and security, record and sign off
13 Commissioning
.1 Care is required on first pressurizing (if not already charged). This and the inspection should be done by a suitably trained and experienced persons eg trained installer who is certified or accepted by body who takes responsibility ie competent inspection body or person- NATA ISI or SISI, others or approved gas cylinder test station (AGCTS)
.2 Inspection by VT is required internally (where possible) and externally to ensure the equipment and installation for design reg, and markings are appropriate for intended service; and there is documentation and spares.
14 Registration
Register ASAP HL A and B accumulators, HL C as convenient or when WHS laws clearly indicate if these are excluded from registration as they are almost always “serially produced”. HL. A, B, C by owner, or as agreed by the user or inspector on the owner's behalf – with the appropriate Regulator.
Note: Omission of registration does not mean they do not require ISI as per AS/NZS 3788 or the owner.
15 Use
.1 Safe use is by WHS law the duty and responsibility of the owner and authorized user and should as far as practical:
a) be in accordance with maker, supplier and installer instructions and with AS 3873 (Ref 3).
b) comply with operating and safety instructions and operated by authorized competent persons trained and instructed with specified duties:
c) have regular operation surveillance. If poor performance is observed it may indicate leak or damaged bladder or seal - advise management.
d) report serious incidents, near misses and accidents as required.
16 In-Service Inspection
.1 Like most plant accumulators can be subject to damage and deterioration and require some inspection.
.2 Supply, Commissioning, 1st year, periodic, damage and repair.
.3 This inspection is needed as Inspection Reports and Certificates are required – installer operators and a competent inspector - certified PE inspectors for HL A and B.
.4 Inspection
a) How: VT, PT, MT, UTT, leak or diameter by tape or calipers. If in doubt UT, pressure test or RT.
b) Externally for:
- Correct identity, marks and labels (repair or replaced if not readable).
- Shell cracks, corrosion (or abrasion eg at straps or other supports), scratches, paint loss, signs of leakage, dents or bulges.
- Safety devices and connections for signs of deterioration. Loose supports or poor protection
c) Internally for:
- Damaged bladder, retaining rings or piston and seals.
- Shell corrosion or score marks.
- Burrs, corroded, crossed or distorted threads.
- Damaged sealing surfaces
d) When: (copy AS/NZS 5788)
e) Criteria: Reject if any damage is considered excessive ie unsafe or poor performance before next inspection. Repair if minor as in 17.
f) If in serious doubt of shell or piston condition, possibly pressure test as for seamless gas cylinders using an Approved Gas Cylinder Test Station (ACGTS) or equivalent.
g) Provide – report eg Appendix A and suitably tag or mark (who did inspection, when done and when next required).
17 Maintenance and Repair
.1 Follow makers instructions, and guidance in Standards Refs 1 and 2
.2 Use a competent body with trained experienced personnel.
.3 Follow safety guides in depressuring and disassembly
.4 Remove light corrosion or scratches in metal by light sanding smooth and then painting or coating to limit corrosion. No welding
.5 Replace Bladder if it fails .eg due to type of service, many cycles, support, type of fluid, bladder material, excess pressure, temperature and aging, or installed incorrectly
.6 Replace damaged safety devices, valves and connections
.7 Replace body or shell when dented, bulged or severely corroded or scratched, or if service has exceeded a specific service life eg over 1million specified pressure cycles.
18 Documentation
.1 Document is required as evidence of compliance and future integrity assessment
.2 This includes essential information and reports ie as listed in Ref 2 including Inspection Reports and Certificates for Supply, Commissioning, 1st year, periodic, and damage/ repair
.3 Computer documentation is preferred with responsibility sign-off for each important stage.
19 Other Accumulator Types
.1 These include welded and fibre reinforced plastic (FRP) accumulators and similar PE types used for the same purpose. Welded types are not common and usually are for lower pressures.
.2 Treat these (or equivalent PE) the same as for high pressure gas accumulators except periodic inspection is usually more frequent and:
a) for welded types particular attention is needed to welded joints for possible fatigue cracking. VT(internal and external), UT, or possibly pressure testing is required as for welded gas cylinders.
b) FRP types particular attention is needed to detect any deterioration of FRP in a similar manner as for high pressure FRP gas cylinders and ensure fixed design life is not exceeded (see Ref 5).
20 Recommendations
.1 Recognise accumulators are hazardous equipment.
.2 Take care at all main stages including initial provision and in overall use.
.3 Use competent experienced bodies and personnel.
.4 Comply with essential safety requirements.
.5 Maintain record of essential documentation.
.6 AU Regulators include any safety issues and numbers in their annual or other reports.
21 Acknowledgment
Thanks to Suppliers and In-service Inspectors for their valuable cooperation and input to this note.
22 References
1 AS/NZS 3788 :2006 Pressure equipment - In-service inspection
2 AS 4343 :2014 Pressure equipment - Hazard levels. (To be issued early 2014)
3. AS 3873: 2001 Pressure equipment - Operation and maintenance.
4. BS ………… Hydraulic Accumulators -
5. ISO
Appendices
A – Suggested Accumulator Inspection Report
APPENDICES
A - SUGGESTED ACCUMULATOR INSPECTION REPORT
(Note: This suggested report covers items for the Record, Report and Certificate - all in one simple document recorded on a standard electronic form during inspection. Issued as final or interim report on site as required by the owner/user. Layout and terms to suit inspection body)
1 Inspection Body Name and address and contact
REPORT DATE and NUMBER
INSPECTION FOR Owner/user name and address and contact and date requested
2 PE
TITLE Accumulator xxxx. See Fig 1
DETAILS Make, model, size, serial no., date of manufacture, design registration no., plant no., location. design pressure, temperature range. material of body and bladder. Registration no. if available
SERVICE Protects ??????, active content, system operating pressure, approx. pulsations/year
HISTORY MDR; sign off and date by supplier and installer; brief details, sign off and date for any significant repairs or change of service
3 Inspection
DATE and INSPECTOR xxxxxxx yyyyyyy
SCOPE Generally in accordance with AS/NZS 3788 - 2006 and owner requirements and maker's recommendations
HAZARD LEVEL zzzzzzzz
EXTERNAL INSPECTION
Markings and notices: (100% VT). eg Identity - OK; location - on shoulder; (durable - for approx 20 years
General condition: (100% VT). eg No significant damage or corrosion; or OK, C (for complies); Good, √ etc.
Coating: (100%VT) eg Thick paint, condition Good
Thickness: (UTT - min. of 4 spots on shell and ends as shown on Fig 2)
1 - Xxmm 2 -xx. 3 - vv. 4 - zz mm (If measured worth recording)
(Add previous results if available to indicate if changed)
Connections: (100% VT) also shake eg OK
Supports: (100% VT) also shake. eg OK, C, Good, √ or acceptable
Safety devices fitted: PRV on pump; pressure guage – eg OK
OPERATIONAL INSPECTION eg Not done; or x
INTERNAL INSPECTION eg. Not open or inspected; or OK by … before closed; or Surfaces OK, new bladder fitted
4 Stamping
Date of trip (…………….)
DATE of NEXT INSPECTION. External- xxxxxx. ; Internal- eg At next opening; or 12 years
5 Recommendations
.1 eg "Next inspection date is extended due to low risk of corrosion, external damage and fatigue provided monitored by user and any maintenance done competently". OR ".....is restricted due to severe service conditions".
New time _________ or ________ replaces report photo _______________________________
.2 PE is to be registered with regulator RRRRR (Required by WHS Law or defer until law clarifies serially produced PE)
5 Certification (ie Assessment)
Accumulator found fit for service until the date of next inspection, provided it is used and maintained properly.
NAME, SIGNATURE, TITLE and QUALIFICATION. eg AICIP SISI No ????
(Explanation of Special symbols used)
6. Figures
Figure 1 PHOTOGRAPH - in colour, with date taken (same as date of inspection to show conditions of inspection and evidence if needed)
Figure 2 Line drawing of accumulator from supplier showing outside, internals with added NDT locations.